link: memory

                          

                      STRUCTURAL BASIS OF THE 'PROCESS OF REMEMBERING' OR 'MEMORY'

                                    

Theme: There are two distinct forms or 'systems' of learning and memory as the process of remembering: non-declarative and reflexive or 'implicit' memory is unconscious remembering; declarative and 'explicit' memory is conscious remembering.

"The brain naturally learns and remembers the moment-to-moment events that constitute life experience. In order to make sense of new experience, the brain attempts to categorize and pattern new information with the information which is already stored in memory. The brain's mechanism of 'patterning' allows for the rapid processing of complex stimuli. At a very high rate of speed, the brain processes new experiential information in the context of previous patterns. Creating spatial maps and patterns, the brain naturally thrives on complexity. In its attempt to process new information from complex sensory input, the brain automatically recalls previously stored programs and formulates new programs. It formulates 'programs' which provide it with crucial information about the surroundings. Allowing for the instant memory of experiences, new information is rapidly processed in the 'spatial memory system' located in the brain's hippocampus. Necessary for survival, the spatial memory system drives the brain's innate search for meaning and is constantly monitoring and comparing the present with past surroundings and experiences. Learning and memory are most effective when facts and skills are 'embedded' in the natural spatial memory and in the context of real life experiences. New learning experiences are naturally 'embedded' in previous learning experiences. With continued learning and experience, the spatial memory system is enriched over time". (Renate Nummela Caine and Geoffrey Caine The Brain: Making Connections Alexandria, Va.: ASCD, 1991, 40-42.)                                                                                   

 The brain has an innate predisposition to search for how things make sense, to search for some meaning of experience. The brain responds to stimuli in the field of focused attention and at the same time absorbs information and signals which are peripheral to the field of focused attention. Many signals perceived peripherally interact with the brain and are processed at the subconscious level  

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notion of localisation of memory as memory trace or 'engram'...   history of 'search for the engram'...

Karl Lashley and his search for the engram...

associative learning and Hebb's learning rule...

molecular activity at synapse as 'memory trace'...

synapse modification or 'neuroplasticity'...   modification of synapses is function dependent...

implications for education...

Traditional paradigm: notion of 'localisation of memory' or 'engram' For most of its history, psychology has been concerned with the study of memory as if it were a static object which could be defined in terms of knowledge that is stored and somehow physically implemented in the brain. Psychologist Gordon Bower (1967) defined the engram in terms of a bundle of features describing an event. 

In the traditional paradigm 'memory' is a noun which represents knowledge stored at specific sites in the brain as the replica of an event... memory trace, memory engram' or 'engram' from German 'engramm' derived from Greek 'gramma' meaning 'something written'. The term was coined in 1908 by German biologist Richard Semon to denote the hypothetical change in neural tissue which corresponds to a memory... to denote the permanent trace left in the brain by a remembered stimulus... permanent physical trace of learning... postulated to account for the persistence of memory as remembered mental stimulus... the conscious recollection or 'memory' of an episode of experience... 'episodic memory'. Ever since medieval times the problem of the 'localisation of memory' has been based on the assumption that there is a one-to-one correspondence between bits of stored information and episodic memories. Numerous attempts have been made to localise the evidence that experience produces permanent modifications in neural tisssue i.e. 'search for the engram'.

For centuries scientists have been striving to answer the question: where is t

he engram and how does it function?

 History of the notion of physiological basis of memory... The idea that memories are stored at specific sites in the brain is an old one. Since medieval times, scientists have tried to localize the physical traces of learning and memory, the 'memory trace'. The mental function of memory was assigned to a specific region of the brain until the middle of the 20th century and  the search for the engram has inspired brain research or 'neuroscience' since its beginnings.

Modern neuroscience begins with the research and theories of German-French physiologist and anatomist Joseph Gall (1758-1828). Gall was interested in brain functions and made the first comparative study of brain anatomy. Gall made the first anatomical and comparative studies of animal brains and proposed that different psychological functions were located in distinct organs of the brain.. He carried out research in what he called 'cranioscopy' - later known as 'phrenology'

Pierre Paul Broca (1824-1880) known for his work on the localisation of brain functions specifically the language function... the 'speech area' or 'Broca's area' in the posterior frontal lobe of the left cerebral hemisphere.

     Russian physiologist Ivan Pavlov used dogs as subjects in his studies on classical conditioning. Pavlov demonstrated that the dogs could be conditioned to salivate at the sound of a bell as a result of associating  the bell ringing with food. In other words the pairing of a conditioned stimulus (food) that normally elicits a conditioned response (salivation) with an unconditioned stimulus (bell ringing) resulted in the association of the unconditioned stimulus (bell ringing) with the conditioned response (salivation)... learning of conditioned responses or conditioned learning... 'conditioned reflex'. The formation and storage of conditioned reflexes ('implicit memory') did not occur after removal of the cerebral cortex.

    American psychologist William James demonstrated the existence of two types of memory... conscious primary memory or 'short-term memory' which lasts a matter of seconds... successive events that result in a continuous experience... secondary memory or long-term memory... permanent memory which is held indefinitely in the unconscious and can be raised to the conscious level or 'consciousness'.

    Karl Lashley and his search for the neural basis of memory or 'search for the engram'. Lashley did not believe in the notion of the engram as localised memory. He believed that learning was a distributed process that could not be isolated within any particular area of the brain... Behavioural scientist and pioneering neuroscientist Karl Lashley student of John Watson (1878-1958) founder of 'behavioural psychology' or 'behaviourism', collaborated with Watson on the first classical conditioning studies done in the US. Lashley, one of the most prominent neuropsychological researchers of his day spent his whole career in an intensive search to localize memory traces. He trained animals to perform specific tasks and lesioned specific areas of the cortex either before or after training and then recorded the effects of the lesions on the animal's ability to remember what they had learned. Lashley summarized 33 years of research and failed efforts to discover the localisation of memory and popularised the term 'engram' in his influential paper 'In Search of the Engram' published in 1950. As a result of his work, he concluded that memories are distributed throughout certain functional areas of the cortex... Furthermore he believed that it was futile to search for a neural basis for memory since behavioural psychology would eventually be reduced to physiology.  His two general principles were as folllows: According to the Equipotentiality Principle memories are not localized but are instead are distributed within functional areas of the cortex ... all cortical areas can be substituted for one another as far as learning is concerned; According to the Mass Action Principle the reduction in learning is proportional to the amount of tissue destroyed, the location of the lesion is not important... increase in disruptive lesions led to reduction in  complex learning. Lashley proposed that learning is an activity of the brain as a whole and that memories are stored in the entire brain rather than at specific sites - an issue which was taken up by American psychologist Karl Pribram.  Despite the controversial nature of his two principles they have contributed nevertheless  to the field of neural network or 'connectionist' research. Lesioning experiments suggest that network processing is distributed and nonlocalized and gives rise to properties of emergence... 'emergent properties'. Lashley's proposal removed the possibility of localizing memory.

In 1949 this view was challenged by  Lashley's student, psychologist Donald Hebb. Hebb proposed that associative learning involved a simple cellular mechanism. 

Associative learning and Hebb's learning rule... Donald Hebb continued the 'search for the engram' and inspired research in the development of a new field - the biology of learning or 'psychobiology'. He presented the most successful theoretical view of the mechanism of learning in his 'Theory of Cell Assemblies' in which he proposed that the sites of memory storage were to be found in assemblies of nerve cells and their connections supporting the view that changes occuring during learning develop among interconnections of neurons throughout wide areas of the brain rather than at one particular area in the brain... reintroducing the idea that it was possible to find the underlying mechanism of learning and memory. His hypothesis known as 'Hebb's learning rule' was also known as the 'pre-post coincidence mechanism'... also the 'pre-post associative mechanism' because it claimed that "coincident activity in both cells involved is critical for strengthening the connections (associations) between the pre-synaptic and post-synaptic neurons...when an axon cell A ...excites cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficacy, as one of two cells firing B, is increased." Particular kinds of learning have been proven to involve the development of particular circuits of neurons.

"Hebb reintroduced the idea that it was possible to find the underlying mechanism of learning. He inspired research in the biology of learning, and the development of a new field - psychobiology. Hebb's work resulted in a continuation of the 'search for the engram.'" (Eric Kandel and Robert Hawkins, "The Biological Basis of Learning and Individuality", Scientific American, 267: 3, Sept 1992, 80.)  

 In the 1950s John Sperry using 'split-brain technique' based on the separation of 'cerebral hemispheres...  studied epileptic patients who underwent surgical removal of the 'hippocampus' and neighboring regions in the 'temporal lobe' of the brain. He discovered that the operation impaired the kind of memory which requires conscious participation i.e. 'explicit memory' thus assigning the function of memory to a specific location in the brain. "An underlying assumption of early studies of memory systems was that the mediation of both explicit and implicit memory involves complex neural circuits". ( Eric R. Kandel and Robert D. Hawkins 'The Biological Basis of Learning and Individuality' Scientific American September 1992 79-86) Neurobiologists are still asking whether each neuronal system is governed by the same or different sets of learning mechanisms or 'rules'.

'Conditioning reflex' as simple associative learning (associating two events)... In l963 Ladislav Tauc and Eric Kandel proposed a second mechanism for associative learning or  'associative learning rule'. While working with the marine snail Aplysia at the Institute Marey in Paris, they found that the synaptic connection between two neurons could be strengthened without activity of the postsynaptic cell when a third 'modulatory neuron', enhances release of neuro- transmitters from the terminals of the presynaptic neuron. They suggested a mechanism of associative learning, the 'pre-modulatory mechanism', which involved coincident electrical impulses in the pre-synaptic neuron and the modulatory neuron. This is the mechanism of the 'classical conditioning reflex' the simplest type of learning as association of  two events.

The model of memory as a static object is no longer considered to be an adequate explanation for the structural basis of memory. In the cognitive paradigm memory represents a dynamic representation of the 'process of remembering'.

 Cognitive paradigm or holistic paradigm: memory as the 'process of remembering'... In the cognitive paradigm 'memory' is a verb which represents a faculty of 'cognition'... the process of 'remembering' how an event is experienced. As a cognitive ability memory is a function of the indifvidual's level of personality development or 'sociocognitive stage'

In the cognitive paradigm a memory is a record of how an event is experienced rather than a replica of the event itself. Memory is the cognitive process of remembering’ a past experience. Knowledge of the experience is somehow encoded in the form of neural patterns resulting from the strengthening of 'synaptic connections' between groups of 'nerve cells' or 'neurons'... the 'engram'. The engram is a representation of a memory or  'memory trace' in the form of some biochemical change that accompanies learning and the retention of learning. This is the 'neural network model' model of memory. Memory as the process of rembering is a unique pattern of neural activity reconstructed from the combination of a 'retrieval cue' and an 'engram'. The retrieval cue is information in the present environment which triggers the process and induces a pattern of activity which is similar to the  pattern which was previously encoded as the engram. The two are combined to form a new neural network. The resulting transient or enduring changes in the brain represent an expression of the way in which an experience is remembered or 'memory'. The memory is a  subjective perception of an event and incorporates the person's thoughts and feelings at the time of the original encoding. The same thoughts and feelings determine the cues which are required to elicit the process of remembering. Retrieval of... recall of 'a memory' depends on the availability of a set of cues which are closely related to the original encoding... reinstatement of adequate 'encoding conditions'.  .

The process of remembering involves the interaction of conscious or 'explicit' memory and unconscious or 'implicit' memory.  'Explicit memory' is memory of conscious learning i.e. 'declarative learning' or 'explicit learning'. Explicit learning is fast. Only one trial is required and that involves the association of simultaneous stimuli permitting the storage of information about a single event. Explicit memory is a function of structures in the 'temporal lobe' of the brain. In contrast 'implicit memory' is memory of unconscious learning i.e. 'non-declarative learning' or 'implicit learning'. Implicit learning does not require conscious participation. Implicit learning is slow. It requires many trials which involve the association of sequential stimuli permitting the storage of information about predictive relations betweeen different events. Implicit memory is expressed through activation of the sensory and motor neuronal systems engaged by the learning task. Implicit learning or 'reflexive learning' can be observed in various 'reflex systems' of both vertebrates and invertebrates.

 The cellular systems for both - the neuronal systems - can store information about the association of stimuli (associative learning and memory)

Short term memory as natural memory system is necessary for survival because it drives the search for meaning of events of life... (as opposed to forced memory or 'rote memorization' associated with compulsory learning or 'schooling'.) which take place in space... hence the 'spatial memory system' also known as 'locale memory system' allows for the instant memory of experience. New information is processed in  in the context of previous patterns of learning which are embedded in previous learning experience. Spatial maps are created and tested to provide   information about the environment... is monitored and compared with past experience.

The spatial memory system relies on the hippocampus in the limbic system,

Emotions cannot be separated from cognition  Emotions are crucial to the process of remembering or 'memory'.

The biological basis of learning. involves changes in the structure of neural pathways or 'networks' resulting from 'synapse modification' i.e. 'neuroplasticity'.  

 Engram as evidence of changes in neural pathways: 'synapse modification' results in 'neuroplasticity' Evidence for changes in neural tissue has been made available only in the past two decades. Recent studies have shown that experience produces permanent modification of the functional connections between neurons in the brain - the 'synapses'. Modification of synapses or 'neuroplasticity' results in changes in the structure of neural circuits or 'neural networks' or 'neuronal systems' which can store information about the association of stimuli i.e. 'associative learning'. Neuroplasticity represents the structural basis of the engram. Learning involves the growth and  ramification of new synapses - 'synaptogenesis' - as well as the modifications of synapses involving   microstructural changes such as increase in size or 'hypertrophy' of existing synapses with the storage of knowledge or 'memory' (as the 'capacity to remember' or 'remembering') and 'the regression of synapses' with the loss of knowledge (as the loss of the capacity to remember or 'forgetting'). The modifiable synapses are the 'spine synapses' on the dendrites...'dendritic spines'... of neurons in the 'hippocampus' of the cerebral cortex.

The physical evidence for learning and memory is in the increase in potent synaptic connections.

 "We are led to conjecture that the structural basis of memory lies in the enduring modifications of synapses, the functional connections between nerve cells. These would involve microstructural changes such as the 'hypertrophy' (increase in size) when memory is stored and regression of synapses in forgetting. The efficacy of synapses could be increased with conditioned activation or 'potentiation.' (John Carew Eccles 1957. "The Physiology of Nerve Cells" Johns Hopkins Press Baltimore 209-211)

"Intelligence and all the other properties of the 'mind' result from the patterns of interconnections and interactions between the nerve cells". (Geoffrey E. Hinton "How Neural Networks Learn from Experience." Scientific American September 1992 145-151)

 Evidence for function-dependent modification of synapses in the cortex (Marion Diamond) studied the brains of rats raised in different environments. There were differences between those raised in cages equipped with facilities for play - complex or 'enriched environment' - and those kept in pairs or in isolation - 'impoverished environment'. Comparisons were made between three groups of littermates. Rats in the first group...the 'control group' were raised in standard laboratory cages - a few rats living in a cage of adequate size with food and water always present; rats of the second group were raised in an enriched environment - several rats living in a large cage furnished with a variety of objects providing stimulation for learning... every day a new set of play things drawn out a pool of 25 objects was placed in the cage; rats of the third group were raised in an impoverished environment... each rat living alone in a cage without any stimulation for learning. Studies were done to determine changes in the synapses of that region of the brain which showed increased brain weight with experience in enriched environments -the 'occipital cortex'. It was discovered that most synaptic connections occurred on the branches or 'dendrites' of the receiving neuron cell or on small projections of the dendrites - the 'dendritic spines'. A comparison of numbers of dendritic spines were made in brain sections of rats living in enriched and impoverished environments by Albert Globus of the University of California at Irvine. Globus compared the numbers of dendritic spines in the 'cortical neurons' or 'pyramidal cells'. He discovered an increase in dendritic spines of 'basal dendrites' when rats were raised in enriched environments. Other investigators also showed increased synaptic contact in the enriched environment group... up to 20% increase in the number of spine synapses and enlargement of the synaptic contact zones... also decreased synaptic contact for te impoverished environment group of rats deprived of stimulation.

The physical evidence for learning and memory is molecular activity at the 'synapse'.

Molecular activity at the synapse constitutes the physical evidence for learning and memory Today the widely accepted view among neurobiologists concerns the molecular events occurring at the synapse which represent the physical trace of learning or 'engram'. Learning is a physiological function of the brain involving the propagation of 'electrochemical signals' or 'nerve impulses' along neurons, and the initiation or 'firing' of new impulses along neighboring neurons as a result of their transmission across the gaps which separate them - the 'synaptic clefts' or 'synaptic connections'.  Learning and memory result from the formation of nerve circuits and networks through the increase of connections between neurons. When stimuli are strong enough to influence the effectiveness of synapses to influence other neurons... when they causes changes in the synapses that facilitate the formation of connections between neurons, then the processes of learning and memory become more efficient.. 'synaptic facilitation'. 

Implications for education: learning from experience or 'experiential learning' involves memory as the 'process of remembering' 'capacity to remember'  Learning from experience -  'experiential learning' - stimulates the growth of new synapses... new synaptic connections.  Experiential learning is 'integrated learning' or 'holistic learning'. Holistic learning involves memory as the capacity... cognitive faculty... the ability to store mental representations of experience important because it forms the basis for learning from experience ...required for adaptation and survival. The capacity for remembering  allows for guidance of behavior on the basis of learning from experience...  Memory as the ability to remember and reflect on experience accounts for human capacity for 'contemplation' or 'inner dialogue'  the basis for human dignity or 'freedom'. Education for freedom is based on recognition and respect for stages of human growth and development - 'sociocognitive stages'. Education of the person 'as a whole' is 'holistic education'.

Learning and memory are most effective when facts and skills are 'embedded' in the natural spatial memory and in the context of real life experiences. Example is the learning of native language. Learning of language occurs by way of internal mental process and social interaction. Social interaction is crucial to effective learning. The system is enriched aver time with learning and experience.  Learning and experience change the structure of the neural networks.

To illustrate the difference between accessing the taxon system and the locale system see fig 8.1page 94 and 8.2 page 96.(Caine) With the locale learning only one trial is needed to recognize the pattern and remember the information. With the taxon system, many trials are needed. To reduce the number of trials for remembering the information, one first has to find or create the pattern by connecting the new information with previously acquired knowedge of the tic-tac-toe diagram.

Recognition of the pattern involves both the intellect and the senses. Natural meaningful brain-based learning involves the conjunction of cognition and emotion. The learner is encouraged to participate actively in his/her own learning... find or create patterns by connecting new information with previousluy acquired knowledge..

Although great strides have been made in the neurosciences, neurobiology and neurochemistry the question still remains to be answered: what exactly are the structural and functional changes in the brain that form the basis of learning and the 'retention of learning' or 'memory'?

 

references Eric Kandel and Robert Hawkins, "The Biological Basis of Learning and Individuality", Scientific American, 267: 3, Sept 1992

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notes

Learning involves a change in the effectiveness of a synapse which causes a change in the influence of one neuron on another. See Eccles and Robinson "The Wonder of Being Human: Our Brain and Our Mind" 128-137 (128) ...synapse

"The brain has an immense capacity to deal with and remember the moment-to-moment events that constitute life experience." (Caine)

Learning is a natural function of the brain which involves the transmission of signals along nerve cells and across their junctional connections, the synapses. Resulting from the activity of nerve cells and their functional junctions are the networks of nerve cells and circuits throughout the brain. The patterns of interconnections and interactions between nerve cells account for the patterns of the 'mind' and the mental processes formed in the brain. The number of nerve cels in the brain - billions - is fixed at birth. No new nerve cells develop. Modification of brain tissue occurs in the synapses. New synapses grow and develop. Experience and learning can cause new synapses to form and grow. As a physiological process, learning is affected by physiological and environmental factors including nutrition, stress, mental state, experiences and circumstances.

Psychologists usually define memory as knowledge stored in the mind, a storage that is physically implemented somehow in the brain. Memory is an extremely important cognitive faculty, because it forms the cognitive basis for learning. Without a way of storing mental representations of the past, we have no way of profiting from experience. But more important, memory frees us from the tyranny of perception, allowing behavior to be guided by the past as well as the present.

Along with consciousness, intelligence, and language, the ability to represent and reflect on the past is the basis for human freedom and dignity.

Classification of Knowledge Stored in Memory The knowledge stored in memory comes in a few basic forms.

Procedural knowledge comprises our repertoire of rules and directions for skilled action, cognitive and motor skills

Declarative knowledge consists of factual knowledge about the world… can be classified into episodic memory (autobiographical memory for one's own actions and experiences) and semantic memory which is more or less generic, abstract knowledge, like a mental dictionary, not tied to any particular event.

The term "memory" usually refers to episodic memory.

For most of its history, psychology has been concerned with episodic memory. And for most of its history, psychology has been concerned with the study of episodic memory as if it were a static object.

In the verbal-learning paradigm of Ebbinghaus (1885/1964), each list of nonsense syllables, and for that matter each individual nonsense syllable, constitutes a separate episode of experience, to be remembered in the context of other episodes; the same is true for the words, pictures, and sentences that constitute the stimulus materials employed in most contemporary studies of memory, more than a century later.

In Ebbinghaus's pioneering book, Uber das Gedachtniss, memory is conceived in terms of an object to be studied. In this tradition (traditional neuroscience) the cognitive psychologist Gordon Bower (1967) defined a memory trace as a bundle of features describing an event. .

neural change linked to memory: a hypothetical physical impression made in neural tissue by a mental stimulus, suggested as an explanation of the persistence of memory.

This model of memory is no longer considered to be an adequate explanation for memory as a ‘process of remembering’.

SYNAPSE The transmission of nerve impulses from one neuron to another occurs at the junction between neurons, the specialized contact points known as 'synapses.' (John Carew Eccles, The Physiology of Nerve Cells, Baltimore: Johns Hopkins Press 1957),

Introduced in 1897, the term 'synapse' is derived from the Greek word meaning 'to clasp.' The synapse has three main components: the point of connection on the 'presynaptic' membrane of an axon terminal, the 'synaptic knob' or 'synaptic button,' the point of connection on the 'postsynaptic' or 'subsymaptic' membrane of a dendrite of the connecting neuron, and a gap which separates them, known as the 'synaptic cleft.' The gap which separates two communicating neurons is a millionth of an inch wide. Nerve impulses or signals are transmitted in the form of electrochemical pulses - a few at a time or in bursts of up to a thousand per second. Incoming signals are collected from other neurons through dendrites. They enter the cell body for processing and are sent outwards through the axon which bifurcates at many points giving rise to numerous 'axon terminals.' At the synaptic junction between neurons, signals pass from the synaptic knob of one neuron and are propagated across the synaptic cleft to the contact point on the connecting neuron. Signals reach the synapse as bursts of electrochemical pulses - so many per second. These do not jump from one neuron to the next. The electrical code of transmission is first changed into the chemical code of transmission. The arrival of electrochemical pulses at the synapse triggers the release of specialized neural transmitter molecules, known as 'neurotransmitters.' These are contained in small vesicles located in the synaptic knob. They are released through the presynaptic membrane and are propagated across the synaptic cleft. They attach to special receptor binding sites on the postsynaptic membrane. Their binding triggers a change in the membrane permeability of the connecting neuron. The binding is excitatory if it causes the movement of electrically charged ions and results in the depolarization of the membrane. A new action potential is generated and the nerve impulse is transmitted.The binding is inhibitory if it results in the further polarization of the membrane. The generation of a new action potential is inhibited and the nerve impulse is not transmitted. Nerve impulses which reach the synapse are subjected to one of two synaptic processes: synaptic excitation or synaptic inhibition. Depending on the process occurring at the synapse, an incoming signal is transmitted to the connecting neuron and fired or not fired. Each neuron has a particular threshold for firing an incoming signal. The transmission of impulses from one neuron to the next depends on the number of electrochemical pulses reaching the synapse. If this number exceeds the critical threshold required for triggering a response in the connecting neuron, then the signal is fired. An impulse is transmitted from one neuron to the next if there are enough pulses to trigger a response and 'fire' the signal. A signal crossing the synapse can have one of two effects: it can have an excitatory effect by lowering the threshold for firing the signal; it can have an inhibitory effect by raising the threshold for firing the signal. The stronger the stimulus, the more pulses are generated. Depending on the number of pulses generated, they initiate or inhibit the 'firing' of new signals along the connecting neuron. Depending on the specific properties of the signal, its electrical effects either inhibit or excite activity in the connecting neuron. The continued transmission of the signal can be either inhibited or enhanced. If the inhibitory input exceeds the excitatory input then a connection is not made between one neuron and the next. If the excitatory input exceeds the inhibitory input then a connection is made between one neuron and the next. Learning ooccurs as a result of changing the effectiveness of synapses so that their influence on other neurons also changes. (Geoffrey Hinton, "How Neural Networks Learn from Experience," Scientific American, 267:3, September 1992, 145)

Learning is a physiological function of the brain involving the transmission of signals along nerve cells and across their junctional connection. The number of nerve cells in the brain is fixed at birth and no new nerve cells grow and develop. Learning and experience change the structure of the neural networks. The number of nerve cells in the brain is fixed at birth and no new nerve cells grow and develop. Learning is a function of stimuli strong enough to influence the effectiveness of synapses in the transmission of signals from one neuron to another across the synaptic clefts. It is a function of the effectiveness of synapses to propagate signals and initiate or 'fire' new signals along neighboring neurons. Wholistic brain-based learning for natural knowledge has meaning for the present and for the future. The brain has an immense capacity to learn and remember in the context of the 'here and now' of space and time. (Renate Nummela Caine and Geoffrey Caine, Making Connections, Alexandria, Va.: ASCD, 1991, 40-42.)

 The brain naturally learns and remembers the moment-to-moment events that constitute life experience. In order to make sense of new experience, the brain attempts to categorize and pattern new information with the information which is already stored in memory. The brain's mechanism of 'patterning' allows for the rapid processing of complex stimuli. At a very high rate of speed, the brain processes new experiential information in the context of previous patterns. Creating spatial maps and patterns, the brain naturally thrives on complexity. In its attempt to process new information from complex sensory input, the brain automatically recalls previously stored programs and formulates new programs. It formulates 'programs' which provide it with crucial information about the surroundings. Allowing for the instant memory of experiences, new information is rapidly processed in the 'spatial memory system' located in the brain's hippocampus. Necessary for survival, the spatial memory system drives the brain's innate search for meaning and is constantly monitoring and comparing the present with past surroundings and experiences. Learning and memory are most effective when facts and skills are 'embedded' in the natural spatial memory and in the context of real life experiences. New learning experiences are naturally 'embedded' in previous learning experiences. With continued learning and experience, the spatial memory system is enriched over time.

 

(Thomas Leahey and Richard Harris, Human Learning. (New Jersey: Prentice Hall, 1989), 256-260.)

 Search for the 'engram' is the search for evidence that experience produces permanent changes in the nervous system and permanent modifications in neural tisssue.

Learning and memory appear to result from molecular changes which take place in the synaptic connections between neurons in the brain. Current research is based on the following working hypothesis: synaptic transmission involves a series of complex molecular events. In the form of an electrochemical pulse, a nerve impulse triggers the influx of calcium ions into the dendrites. The calcium combines with a recently discovered protein called 'calmodulin.' The calciumcalmodulin complex has a powerful metabolic action which results in the manufacture of proteins and other macromolecules. These are instrumental in increasing the potency of the synapses and in increasing their numbers. It is generally conjectured that the physical evidence for learning and memory is in the increase in potent synaptic connections. New synapses grow and develop. The modifiable synapses are the 'spine synapses' on the dendrites of neurons in the cerebral cortex and the hippocampus. Modifications are manifest in the growth and ramification of new synapses and in the hypertrophy of existing synapses. Regression of synapses occurs with forgetting. There is evidence for this function-dependent formation of synapses in the cortex.21 In studies of rats raised in different environments, there were differences between those raised in a complex environment - in cages equipped with facilities for play - and those kept in pairs or in isolation. Rats raised in the complex environment had developed a 20% increase in the number of spine synapses and the synaptic contact zones were enlarged. There was a decrease in the number of synapses when the rats were deprived of stimulation. Although great strides have been made in the neurosciences, neurobiology and neurochemistry, the question which still remains to be answered is the following: what are the structural and functional changes in the brain that form the basis of learning and memory?

 

 

Wholistic brain-based learning for natural knowledge has meaning for the present and for the future. The brain has an immense capacity to learn and remember in the context of the 'here and now' of space and time. (Renate Nummela Caine and Geoffrey Caine, Making Connections,  Alexandria, Va.: ASCD, 1991, 40-42.) The brain naturally learns and remembers the moment-to-moment events that constitute life experience. In order to make sense of new experience, the brain attempts to categorize and pattern new information with the information which is already stored in memory. The brain's mechanism of 'patterning' allows for the rapid processing of complex stimuli. At a very high rate of speed, the brain processes new experiential information in the context of previous patterns. Creating spatial maps and patterns, the brain naturally thrives on complexity. In its attempt to process new information from complex sensory input, the brain automatically recalls previously stored programs and formulates new programs. It formulates 'programs' which provide it with crucial information about the surroundings. Allowing for the instant memory of experiences, new information is rapidly processed in the 'spatial memory system' located in the brain's hippocampus. Necessary for survival, the spatial memory system drives the brain's innate search for meaning and is constantly monitoring and comparing the present with past surroundings and experiences. Learning and memory are most effective when facts and skills are 'embedded' in the natural spatial memory and in the context of real life experiences. New learning experiences are naturally 'embedded' in previous learning experiences. With continued learning and experience, the spatial memory system is enriched over time.

 

Since medieval times, scientists have tried to localize the physical traces of learning and memory, the 'memory trace.' The 'search for the engram' has inspired brain research since its beginnings. Modern neuroscience begins with the research and theories of Joseph Gall (1758-1828) He made the first anatomical and comparative studies of animal brains. He believed that different psychological functions were located in distinct organs of the brain. Pierre Paul Broca (1824-1880) Karl Lashley  was a student of John Watson (1878-1958), the founder of behaviorism They collaborated on the first classical conditioning studies done in the US. Lashley believed that eventually behaviorist psychology would be reduced to physiology making the concept of 'search for the engram' a futile one. He proposed that learning is an activity of the whole brain.  Memories are stored in the entire brain and not at specific sites. The task of finding a neural basis for memory seemed hopeless. Lashley's proposal removed the possibility of localizing memory - of finding 'the engram.' His student, psychologist Donald Hebb, proposed that the sites of memory storage were to be found in assemblies of nerve cells and their connections. Hebb reintroduced the idea that it was possible to find the underlying mechanism of learning. He inspired research in the biology of learning, and the developnment of a new field - psychobiology.    Hebb's work resulted in a continuation of the 'search for the engram.' (Eric Kandel and Robert Hawkins, "The Biological Basis of Learning and Individuality", Scientific American, 267:  3, Sept 1992, 80.) In 1949 he proposed that associative learning involved a simple cellular mechanism. According to his hypothesis, known as the 'pre-post coincidence mechanism,'  coincident activity in both cells involved is critical for strengthening the connections between the presynaptic and post-synaptic neurons. "When an axon cell A ...excites cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficacy, as one of two cells firing B, ois increased." In l963 Ladislav Tauc and Eric Kandel proposed a second mechanism for associative learning. While working with the marine snail Aplysia at the Institute Marey in Paris, they found that the synaptic connection between two neurons could be strengthened without activity of the postsynaptic cell when a third 'modulatory' neuron, enhances transmitter release from the terminals of the presynaptic neuron. They suggested a mechanism of associative learning, the 'pre-modulatory' mechanism, which involved coincident electrical impulses in the pre-synaptic neuron and the modulatory neuron. This is the mechanism of the classical conditioning reflex, the simplest example of learning to associate two events.

 

    Today the widely accepted view among neurobiologists concerns the molecular events in the synapse.(Ibid.,

 

LEARNING AND MEMORY As natural functions of the brain, the processes of learning and memory did not develop by accident; they developed because they were of survival value. As a product of human evolution through natural selection, the brain can best be understood as an organ of learning, adapted for the survival of the species.( Gerald Fischbach, "Mind and Brain", Scientific American, 267: 3, Sept 1992,)

Affected by physiological as well as environmental factors, the learning function of the brain is as natural as the breathing function of the lungs. The brain responds automatically to the complexity of stimuli in its search for meaning in the complex environment in which it is immersed. It processes many incoming stimuli simultaneously - those which deal with body functioning and health maintenance at the same time as those which deal with the intellect and the emotions. It consciously responds to stimuli in the field of focused attention and subconsciously to peripheral stimuli.

In the course of human evolution, survival has depended on behavioral adaptation. Human adaptive behavior has depended on the brain's capacity to make decisions. The brain's decision making function has depended on its capacity to derive meaning from a complex environment. The brain's innate drive to search for meaning in the environment comprises the driving force behind the highly developed mental processes of learning and memory. Effective learning from experience results in adaptive changes of behavior. The human aspects of human behavior and human nature are derived from the brain's ability to learn and to recall what is learned. Derived from the brain's innate drive to search for meaning in a complex environment, the brain's 'time-binding' function of learning and memory depends on its ability to process complex information. Effective learning has depended on the brain's capacity to seek patterns and detect them as quickly as possible. Efficient learning has depended on the functional integration of the brain's cognitive and emotional states. Complex environmental stimuli are rapidly processed in their emotional context. The brain's pattern seeking capacity, hence its learning ability, is influenced by its affective states. The learning process involves the combined functioning of the intellect, the emotions and creative capacities. The brain's capacity for learning is enhanced by challenge and inhibited by threat. Learning is also enhanced by an alternation of different states of consciousness - rational waking state, creative state, meditative state, dream state, etc. The different states of consciousness are influenced by physical wellbeing and emotions. In each state a different part of the brain is dominant, but the brain functions as a whole.

   

 

 

synaptic facilitation

The process by which neural activity causes structural changes in the synapses that facilitate more efficient learning and memory.

The Experience of Remembering

A big shift in perspective was announced by Frederick C. Bartlett (1932), almost 50 years after Ebbinghaus published his book. It is evident in the very title of Bartlett's book: Remembering, and it is clear in Bartlett's first chapter, which is a scathing attack on poor old Ebbinghaus: The results of the nonsense syllable experiments may throw light upon the... establishment and the control of [very special habits of reception and repetition], but it is at least doubtful whether they can help us see how, in general, memory reactions are determined.For Bartlett, memory is not a thing, labeled by a noun, but rather an activity, labeled by a verb. Memories are things people have, but remembering is something people do. Referring back to the library metaphor, memory is not like a book that we read, but rather it's like a book that we write anew each time we remember. One's memory may be based on fragmentary notes supplied by the memory trace, but (as Jerome Bruner might have put it) remembering involves "going beyond the information given" there. In the famous "trash bag" scene of the film American Beauty (1999), one of the characters says that "video is a poor excuse, I know, but it helps me to remember". So it is with the memory trace, in Bartlett's view. The memory trace supports remembering, but it's not all there is to memory.

Bartlett's view adds a new Reconstruction Principle to our list of the operating principles in memory: One's memory of an event reflects a blend of information contained in specific traces encoded at the time it occurred, plus inferences based on knowledge, expectations, beliefs, and attitudes derived from other sources.In other words, remembering is more like making up a story than it is like reading one printed in a book. For Bartlett, every memory is a blend of knowledge and inference. Remembering is problem-solving activity, where the problem is to give a coherent account of some past event, and the memory is the solution to that problem.In  some sense, the conflict between Ebbinghaus and Bartlett was more apparent than real. Ebbinghaus knew perfectly well that nonsense syllables left something important out of memory, and Bartlett knew perfectly well that something like Ebbinghaus's methods were necessary for proper experimental research. And it's clear that reconstructive processes can be studied within the constraints of the traditional verbal-learning paradigm.Consider, for example, the notion that there are two expressions of episodic memory: as defined by Daniel Schacter (1987), explicit memory entails conscious recollection of some past event, as in recall or recognition; by contrast, implicit memory is represented by any change in experience, thought, or action which is attributable to that event, as in repetition or semantic priming effects. Explicit and implicit memory can be dissociated such that we can observe priming effects in amnesic patients who cannot recall or recognize the prime. This has led some theorists to propose that explicit and implicit memory are mediated by separate and independent memory systems. It turns out, however, that explicit and implicit memory interact, so that subjects can strategically capitalize on implicit memory to support their performance on an explicit memory task.

The basis for this view lies in George Mandler’s (1980) two-process theory of recognition. According to Mandler, recognition is a judgment of prior occurrence which is based on two processes: familiarity, as when something you encounter "rings a bell", leading you to believe that you have encountered it before; and retrieval, or conscious recollection based on recovery of episodic trace information. Retrieval obviously constitutes explicit memory, while familiarity has the character of priming. But if recognition can be mediated by either familiarity or retrieval, then recognition ought to be possible in amnesia, provided that amnesic patients are encouraged to strategically capitalize on the perceptual and conceptual salience which comes with priming.This point was made convincingly in a study by Jennifer Dorfman, a student of Mandler’s who spent time in my lab at Arizona. Dorfman worked with a group of psychiatric patients receiving electroconvulsive therapy (ECT) for depression. It is well known that ECT produces both an anterograde and a retrograde amnesia affecting explicit memory but sparing implicit memory. In her experiment, the subjects studied a wordlist immediately before receiving ECT; then their memory was tested in the recovery room by means of matched explicit and implicit tests.For the explicit test, the patients were presented with three-letter stems of list items and control words, and asked to remember a word from the study list that began with the stem. As expected, their performance was very poor. For the implicit test, the patients were presented with the same sorts of stems, but now they were asked to generate the first word that came to mind. On this task, the subjects showed a priming effect, completing more critical than neutral stems with the target wordThe subjects also received a test of recognition. For half of the items, they were asked to adopt a conservative criterion, endorsing an item only when they were absolutely sure that it had been on the study list. For the remainder, they were instructed to adopt a more liberal criterion, saying "yes" if an item seemed familiar, even if they were uncertain. There was much better recognition under the liberal criterion, as might have been expected, but this improvement was not merely an artifact of response bias, because false alarms did not rise along with the hits.Here we have an interesting case in which, contrary to the claims of traditional signal-detection theory, sensitivity does indeed change with a shift in criterion. But the more important finding, in the present context, was that recognition improved -- provided that the patients were encouraged to capitalize on the feeling of familiarity that comes with priming. Recognition by familiarity is essentially a reconstructive, problem-solving process, in which people are trying to give the best possible account of the past, given all of the information available to them.In fact, recent research on recollective experience, or the phenomenal experience of remembering, makes clear that the precise quality of the memory, and the person’s confidence in it, will depend on its informational base. I’m thinking, for example, of the distinction drawn by Endel Tulving (1985) between remembering, or one’s concrete awareness of the past (entailing what Tulving calls "autonoetic consciousness", knowing, or one’s abstract knowledge of the past (entailing what Tulving calls "noetic consciousness"), and doing, or memory as expressed in performance (entailing what Tulving calls "anoetic" consciousness). John Gardiner (1988) has developed this distinction further, but while Tulving and Gardiner use the same "remember/know" vocabulary, they are talking about quite different phenomenal experiences. For Tulving, "knowing" is really knowing, one’s abstract knowledge of an event, based on something like semantic memory. Knowing our personal past, in this respect, is like knowing that Columbus discovered America in 1492. But Gardiner’s "knowing" is really feeling, an intuition that an event occurred, based on something like implicit memory.So even though Tulving and Gardiner only distinguish between "remembering" and "knowing", there are actually three varieties of recollective experience, or memory "qualia": remembering, or conscious recollection of some past event; knowing, or abstract knowledge of that event; and feeling, an intuition that an event occurred.

Traditional experiments on remembering and knowing do not make this critical distinction between knowing and feeling, but a line of research by Mike Kim and myself has done so (Kihlstrom & Kim, 1998; Kihlstrom, Kim, & Dabady, 1996; Kim & Kihlstrom, 1997). Our studies involved an extension of the Tulving/Gardiner paradigm: in the typical experiment, subjects studied a list of words under a levels of processing manipulation; after a 24-hour retention interval they performed a yes/no recognition task. They were also asked to report their recollective experiences, which we illustrated by analogy to a multiple-choice test. Sometimes, you just know the answer; sometimes, you actually remember learning the material, such as where it appeared on a page in your textbook. And sometimes, an answer just "rings a bell", so you feel it must be the right choice. If we look at overall recognition, we get the expected levels effectBut if we then distinguish among the varieties of recollective experience, we get a dissociation by level of processing: semantic processing favors remembering and knowing, while phonemic processing favors feeling. In a series of experiments, Kim and I have shown that feeling can be dissociated from remembering and knowing by a number of factors besides level of processing: amount of study, criterion shifts, confidence levels, and response latencies. But in all these experiments remembering and knowing behave in pretty much the same way. Recently, however, we have been able to dissociate remembering from knowing by a somewhat boring task: 15 study-test cycles with a 20 item list, each study trial followed by a recognition test and ratings of recollective experience. Memory improved over trials, of course, but the most important changes had to do with recollective experience. On initial trials, we see the familiar mix of remembering, knowing, and feeling; but on later trials, feeling drops out of the picture, and remembering is replaced by knowing. By the end of the 15 trials, the subjects aren’t remembering anything: they know the contents of the study list, the way they know the list of state capitals.

The feeling of knowing is aptly described in the Rodgers and Hart song "Where or When", from their musical Babes in Arms (1937):An automatic retrieval process ‘associative retrieval’ occurs when a ‘retrieval cue’ automatically triggers an experience of remembering. More on Remembering & Forgetting:Associative retrieval is an automatic reminding process. It occurs when a cue automatically triggers an experience of remembering. Strategic retrieval is a slow deliberate search of memory to generate hints and retrieval cues. Strategic retrieval interrogates the automatic retrieval process.The Engram - Memory Trace: Encoding the experience strengthen the connections between groups of neurons. The resulting transient or enduring changes in our brains are called engrams. The engram is the representation of a memory in the brain. A retrieval cue induces a pattern of activity: if this pattern is similar to a previously encoded pattern you remember the event.The "memory" in a neural network model is a unique pattern reconstructed from the cue and the engram. There is no one-to-one correspondence between a bit of information stored away and the conscious recollection of a experience. "A neural network combines information in the present environment with patterns that have been stored in the past, and the resulting mixture of the two is what the network remembers."Memories are records of how we experienced events, not replicas of the events themselves.

Encoding specificity principal: In order for us to remember, there must be a similarity or affinity between encoding and retrieval process. "The specific way a person thinks about or encodes an event determines what 'gets into' the engram, and the likelihood of later recalling the event depends on the extent to which a retrieval cue reinstated or matches the original encoding." person's subjective perception of an event, including thoughts, fantasies, or inferences occurred at the time of encoding, determines the cues to elicit recalls. Only a subset of cues that are closely related to the original encoding must be available. Retrieval will fail, if encoding conditions are not adequately reinstated at the attempted recall. Extensive elaborate encoding does not help if cues aren't available to elicit recalls. "Elaborate encoding yields higher level of explicit memory than non-elaborate encoding, probably because a rich & elaborate encoding is accessible to a broad range of retrieval cues, whereas a shallow encoding can be elicited only by a few perfect matched cues."There are two theories of forgetting: one theory is that everything is permanently stored in the mind, and the other theory is that some information maybe lost from memory forever. According to the first theory, we do not remember because we do not have something (cues) that reminds us of an event or experience. If we search for cues, we are able to access the information: nothing will be lost forever. The second theory holds that once we forget something, it is lost and never recovered. Sometimes, we forget because the right cues are not available, but it is also likely that sometimes we forget because the relevant engrams have weakened or become blurred. Therefore, the second theory is probably realistic.Source(s): Daniel L. Schacter, "Searching for memory: the brain, the mind, and the past", (New York, 1996).

Engram: An enduring change in the brain postulated to account for the persistence of memory. The term "engram" was coined in 1908 to denote the permanent trace left in the brain by a remembered stimulus, the lasting latent memory engraved into the psyche. An engram is a memory trace, one possible explanation for the persistence of memory. Fundamentally, an engram is posited to be a physical, biochemical change in the brain (and other neural tissue) in response to external stimuli, thus forming a memory. arl Lashley coined the term and did extensive research to localize engrams in the 1920s. 1 Saint Mary's University, Department of Psychology, Halifax, Canada In his well-known article In Search of the Engram published in 1950, Karl Spencer Lashley summarized his 33 years of research and theory on memory and the brain. He concluded that (1) memories are not localized but are instead distributed within functional areas of the cortex and (2) memory traces are not isolated cortical connections between inputs and outputs. Though not the first time he had expressed such convictions, their reiteration in this article was backed by Lashley's estimable reputation and expressive power and they have taken firm root in the collective knowledge of today's memory and neuropsychological research community. Famous People and Their Contributions to the Study of Memory Ivan Pavlov, Karl Lashley, Donald Hebb William James

An intriguing question that scientists and psychologists alike have been striving to answer for centuries is how and where memory processes occur in the brain. Many individuals have devoted their knowledge, time, and talents to this study and will be remembered for their research contributions. vlov and His Famous Dog Studies Ivan Pavlov was a Russian physiologist who is famous for his numerous studies on classical conditioning. Using dogs as subjects, Pavlov paired a conditioned stimulus (food) that normally elicited a conditioned response (salivation) with an unconditioned stimulus (bell ringing). Eventually, the unconditioned stimulus became associated with the conditioned response. Pavlov further conducted research on classical conditioning. It was determined from research done by Pavlov that learning done through classical conditioning occurred in the cerebral cortex. Work by Pavlov proved that conditioned responses could not be learned by dogs after removal of the cerebral cortex. Thus the cerebral cortex was determined to be critical for the formation and storage of conditioned reflexes. arl Lashley and "The Search for the Engram" Karl Lashley was a stimulus-response behaviorist. He theorized that physical memory traces (engrams) must be made in the brain when learning occurs. These ne connections of neurons were assumed to involve the cerebral cortex, as proven by studies conducted by Pavlov. In 1929, Karl Lashley wrote his famous monograph, "Brain mechanisms and intelligence." This work consisted of studies with rats and mazes. Lashley removed portions of the cerebral cortex, varying from 10-50% in an effort to study the role the cerebral cortex played in learning. These studies brought about two important theories. The first theory, entitled Principles of Mass Action, proved that the amount of cortex removed was critical to the learning abilities of the rats. The second theory, entitled Equipotentiality, proved that all areas of the cortex are equally important to learning, or no area was proven to be more important than any other area.Studies with the central nervous system further support the existence of engrams in the brain. All behavior reflects actions of the nervous system and because the nervous system is a physical-chemical system, changes in behavior from learning must cause physical-chemical alterations. Therefore, all learning must involve alterations between input and output of the central nervous system. Engrams must exist. However, Lashley was never able to find the existence of an engram and concluded therefore that "the necessary conclusion is that learning just is not possible." The engram has still never been found, but groundbreaking research has been conducted that has begun to substantiate the theories of Lashley. Hebb and The Theory of Cell Assemblies Hebb presented the most successful theoretical view of the general nature of the engram in 1949 as his "Theory of Cell Assemblies." It is clear that the engram does not develop at one particular area in the brain. Hebb's theory supports the view that changes that occur during learning develop among interconnections of neurons throughout wide areas of the brain. Particular kinds of learning have been proven to involve the development of particular circuits of neurons. The engram does not appear to be localized, but its existence cannot be questioned. William James and Dichotomous Memory Studies by James proved the existence of at least two types of memory. The first type of memory defined by James was primary memory, or what we now call short-term memory. This is defined as material that lasts a matter of seconds. Primary memory consists of successive events in our environment that span all the senses and result in a continuous experience. Material in primary memory has not yet left consciousness. James defined a second type of memory as secondary memory. This consists of long-term memory, or permanent memories. This material is held indefinitely and does not reside in consciousness, but is available to bring to consciousness if desired. It is known that memory has several time constants. However, it is unknown if James's two aspects of memory are two different processes or the same process over different time spans.