Memory
Memory • A few definitions. • Memory: information that is stored (e. g. the memory of grandmother) or the structure that stores this information ( e. g. the strength of synapsesin in a particular part of the brain ) • Learning: the storage process (e. g. what mediates a change in synaptic strength) Remembering: the retrieval of stored information
Types of Memory • Hebb (1949) differentiated between two types of memory: • Short-term memory – memory of events that have just occurred. • Long-term memory – memory of events from previous times. • Short term / Working memory • Long Term • Two types of long term memory are procedural and declarative.
Types of Memory • Later research has weakened the distinction between STM and LTM. – Some memories do not qualify as distinctly short-term or long-term. • Working Memory – Proposed by Baddeley & Hitch as an alternative to short-term memory. – Emphasis on temporary storage of information to actively attend to it and work on it for a period of time.
Amnesia • Amnesia is the loss of memory. • Studies on amnesia help to clarify the distinctions between and among different kinds of memories and their mechanisms. • Different areas of the hippocampus are active during memory formation and retrieval. – Damage results in amnesia.
Brenda Milner's famous patient H. M. • • • To relieve epilepsy, H. M. ‟s medial part of temporal lobe and hippocampus were removed bilaterally. This had an unexpected effect on one type of memory. Not affected by lesion. Working: e. g. remembers names for as long as not distracted. Old Procedural: e. g. language normal New Procedural: can learn new sports Old Declarative: e. g. recognises his mother. Affected by lesion. New Declarative: e. g. cannot remember new acquaintances The lesion of the hippocampus produced anterograde amnesia.
Brenda Milner's famous patient H. M. • Patient HM is a famous case study in psychology who had his hippocampus removed to prevent epileptic seizures. • Afterwards Patient HM had great difficulty forming new long-term memories. • STM or working memory remained intact. • Suggested that the hippocampus is vital for the formation of new long-term memories.
Brenda Milner's famous patient H. M.
Brenda Milner's famous patient H. M. • Patient HM showed massive anterograde amnesia after the surgery. • Two major types of amnesia include: • Anterograde amnesia – the loss of the ability to form new memory after the brain damage occurred. • Retrograde amnesia – the loss of memory events prior to the occurrence of the brain damage.
Brenda Milner's famous patient H. M. • Patient HM had difficulty with declarative and episodic memory. – Episodic memory: ability to recall single events. – Declarative memory: ability to put a memory into words. • Patient HM’s procedural memory remained intact. – Procedural memory: ability to develop motor skills (remembering or learning how to do things).
Brenda Milner's famous patient H. M. • Patient HM also displayed greater “implicit” than “explicit” memory. • Explicit memory – deliberate recall of information that one recognizes as a memory. • Implicit memory – the influence of recent experience on behavior without realizing one is using memory. • Recall –воспроизводить • Deliberate – осмысленно, осознанно
Function of the hippocampus • Research of the function of the hippocampus suggests the following: 1. The hippocampus is critical for declarative (especially episodic) memory functioning. 2. The hippocampus is especially important for spatial memory. 3. The hippocampus is especially important for configural learning and binding (связывание).
Short term / Working memory • A sort of scratch pad which allows for temporary storage of information. • Example 1: storing numbers when adding. • Example 2: storing words that one reads to form a meaning full sentence. • Example 3: spatial location of objects when you close your eyes and point to remembered objects. It involves the frontal lobe and has a very limited capacity (e. g. limited to about a 9 digit new ).
Long Term • Two types of long term memory are procedural and declarative.
Procedural (knowing how) • Characteristics: • includes skills such as skiing • established slowly by practice • one is not conscious of remembering the skill • starts to develop at birth • is not affected in amnesia • is coded and stored in much of the CNS, for example, the tuning of binocular V 1 cells during the critical period for stereopsis and in the cerebellum and motor cortex for motor skills.
Declarative (knowing that) • Characteristics: • representations of objects and events e. g. face of a friend • involves associations e. g. name with face • often established in one trial • one is conscious of remembering • starts only after the age of 2 yrs • affected by amnesia • learning involves the hippocampus in medial part of the inferior temporal lobe. • memories are stored in all the association areas but in particular in the inferior temporal lobe.
Two types of declarative memory are semantic and episodic. • Semantic • Characteristics: • Remembering faces and places. • Remembering facts and concepts. • The visual aspects of familiar places are recognized and stored in the parahippocampal place area (PPA) in medial areas of the inferior temporal lobe. • Those of familiar faces in the fusiform face area (FFA) in more lateral areas
Two types of declarative memory are semantic and episodic • • Characteristics (episodic) : Remembering particular objects and places in one‟s personal past. Episodic are composed of several semantic memories. Associating who and what with where and when. Examples: In episodic memory one not only recognizes the person in the picture but also when the picture was taken. “We visited Paris when the kids were young”. The sequence of places one passes while walking across a city. The synthesis of such representations provides us with a map of the spatial layout of the city.
Working memory • Working memory is subdivided into several compartments. Three compartments are: • Spatial Locations • Words • Visual Objects • Short term working memory involves reverberating circuits. In such a circuit, activity continues long after input/sensation ends.
Long Term Memory • Long term memory involves semi permanent changes in synaptic strength between assemblies of neurons.
Storing Information in the Nervous System • Activity in the brain results in physical changes. • Patterns of activity leave a path of physical changes. • Not every change is a specific memory as was once originally believed.
Storing Information in the Nervous System • A Hebbian synapse occurs when the successful stimulation of a cell by an axon leads to the enhanced ability to stimulate that cell in the future. – Increases in effectiveness occur because of simultaneous activity in the presynaptic and postsynaptic neurons. – Such synapses may be critical for many kinds of associative learning.
Storing Information in the Nervous System • Studies of how physiology relates to learning often focus on invertebrates and try to generalize to vertebrates. • The aplysia is a slug-like invertebrate that is often studied due to its large neurons. • This allows researchers to study basic processes such as: – Habituation. – Sensitization
Storing Information in the Nervous System • Habituation is a decrease in response to a stimulus that is presented repeatedly and accompanied by no change in other stimuli. – Results in a change in the synapse between the sensory neurons and the motor neurons. – Sensory neurons fail to excite motor neurons as they did previously.
Storing Information in the Nervous System • Sensitization is an increase in response to a mild stimulus as a result to previous exposure to a more intense stimulus. • Changes at identified synapses include: – Serotonin released from a facilitating neuron blocks potassium channels in a presynaptic neuron. – Prolonged release of transmitter from that neuron results in prolonged sensitization.
Storing Information in the Nervous System • Long-term Potentiation (LTP) occurs when one or more axons bombard a dendrite with stimulation. – Leaves the synapse “potentiated” for a period of time and the neuron is more responsive. • Properties of LTP that suggest it as a cellular basis of learning and memory include: – Specificity – Cooperativity – Associativity
Storing Information in the Nervous System – Specificity – only synapses onto a cell that have been highly active become strengthened. – Cooperativity – simultaneous stimulation by two or more axons produces LTP much more strongly than does repeated stimulation by a single axon. – Associativity – pairing a weak input with a strong input enhances later responses to a weak input.
Storing Information in the Nervous System • Long-term depression (LTD) is a prolonged decrease in response at a synapse that occurs when axons have been active at a low frequency. – The opposite of LTP
Storing Information in the Nervous System • Biochemical mechanisms of LTP are known to depend on changes in glutamate synapses primarily in the postsynaptic neuron • This occurs at several types of receptor sites including the ionotropic receptors: – AMPA receptors. – NMDA receptors.
Storing Information in the Nervous System
Storing Information in the Nervous System • LTP in hippocampal neurons occurs as follows: – Repeated glutamate excitation of AMPA receptors depolarizes the membrane. – The depolarization removes magnesium ions that had been blocking NMDA receptors. – Glutamate is then able to excite the NMDA receptors, opening a channel for calcium ions to enter the neuron.
Molecular basis of Long Term Memory • The key in long term learning is the NMDA receptor which opens only when the cell is strongly depolarised. • If two synapses fire at the same time (synchronously) they produce a larger depolarization than if they fire at different times (asynchronously). • Cells that fire together wire together. • This is the basis for plasticity or learning throughout the CNS.
Storing Information in the Nervous System – Entry of calcium through the NMDA channel triggers further changes. – Activation of a protein that sets in motion a series of events occurs. – More AMPA receptors are built and dendritic branching is increased. • These changes increase the later responsiveness of the dendrite to incoming glutamate.
Storing Information in the Nervous System • Changes in presynaptic neuron can also cause LTP. • Extensive stimulation of a postsynaptic cell causes the release of a retrograde transmitter that travels back to the presynaptic cell to cause the following changes: – Decrease in action potential threshold – Increase neurotransmitter release of – Expansion of the axons. – Transmitter release from additional sites
Storing Information in the Nervous System • LTP changes behavior by creating changes in multiple synapses and complex networks of neurons. • Understanding the mechanisms of changes that enhance or impair LTP may lead to drugs that improve memory. – Example: Mice with genes that cause abnormalities in the NMDA receptor learn slowly and extra NMDA receptors result in faster learning.
Where are these modifiable synapses located? • Examples of three different skills. • 1. Motor Cortex. • For motor skills, like a sequence of finger taps, the synapses undergoing plastic changes are distributed in various motor areas. • One key area is primary motor cortex. • After training, a larger area is activated in the hand area of motor cortex when the trained sequence is performed than for a naive sequence. • In violinists, who use their left hand for fingering, the hand area in the right motor cortex (the side controlling the left hand) becomes larger than that on the left
Auditory Cortex • When trained to discriminate between slightly different frequencies of sound, around a mean frequency, one's ability to discriminate frequencies improves. • This improvement is specific for frequencies near the mean training frequency. • Training causes expansion of the region representing this frequency in the primary auditory cortex (A 1).
Visual Cortex • You can also improve your vision by training. Your ability to detect a break in a line improves with practice. • This improvement is specific for the orientation that you trained for. • This improvement involves plasticity in primary visual cortex.
Working memory in the frontal lobe is critical in decision making. • • • The sound triggers one's long term memory of a phone. Visual inputs are recognised by the para hippocampal place area as those of your house. The frontal lobe with these working memories decides that the appropriate action in this context is to pick up the phone. Suppose the phone rings while you are at your friend's house. Again, the sound triggers one's long term memory of a phone. Visual inputs are recognised by the parahippocampal place area as those of your friend's house. The frontal lobe with these working memories decides that the appropriate action in this context is not to pick up the phone. Working memory allows us to organize things we remember. This process is critical in decision making.
The amygdala is involved in learning emotional responses • The amygdala is essential for the acquisition and expression of conditioned emotional responses
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