Memory and the Brain

Question 1

engram

Answer 1

a means by which memory traces are stored as biophysical or biochemical changes in the brain (and other neural tissue) in response to external stimuli

Question 2

lashley

Answer 2

challenged localizationism w/ mass action principle;

series of experiemnts:
make knife cuts in the cortex of a rat’s brain that would disconnect the sensory regions from the motor regions of the cortex OR remove parts of the cortex of varying size/location,

either before or after rats had learned to run mazes of varying difficulty;

locations of lesions didn’t matter much - only the extent of tissue destruction and complexity of the task

Question 3

mass action principle

Answer 3

principle that the reduction in learning is proportional to the amount of tissue destroyed, and that the more complex the learning task, the more disruptive the lesion.

Question 4

graceful degradation

Answer 4

property of neural networks that mass action principle seems to resemble where damage to a few processing components does not produce major disruption of function.

Question 5

“knowledge domains” hypothesis

Answer 5

hypothesis of “some scientists” that engrams are distributed according to knowledge domains - very specific semantic or object categories/domains

more speculative version of the more broadly held, modern claim that memories are stored primarily within the brain regions originally involved in processing

Question 6

Hebb’s theory

Answer 6

hypothesized that memories are stored in the brain in the form of networks of neurons he called “cell assemblies” that are formed through Hebbian learning: cells that fire together, wire together

Question 7

eric kandel

Answer 7

did californian sea slug withdrawal reflex experiments to examine basic forms of learning (habituation and sensitization)

Slugs withdraw their gills when its siphon is touched and can be habituated to not make that response; however by associating touch w/ a shock to the tail sensitizes the reaction.

Question 8

habituation

Answer 8

a reduced response when the same stimulus is repeated over and over;

involves a decrease in neurotransmitter release at the sensory neuron-motor neuron synapse

Question 9

sensitization

Answer 9

an increased response to a habituated stimulus when it is paired w/ an aversive stimulus such as shock;

involves an increase in neurotransmitter release, but depends on the activity of additional neurons; a tail shock excites different sensory neurons, which in turn excite modulatory interneurons that increase neurotransmitter release from the siphon sensory neurons, enhancing reflex;

Question 10

long-term potentiation

Answer 10

a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously, particularly by a single high-frequency stimulus

seems to model memory well because:

• seems to mimic phenomenon of single-event memory
• can last for days or even weeks (though longer-term memory requires changes in gene expression, synaptic connectivity, etc.)
• has specificity and associativity

Question 11

specificity

Answer 11

only synapses activated during stimulation are enhanced

other synapses - even those on the same neuron - are not affected

works w/ specificity of memories

Question 12

associativity

Answer 12

findings that if one pathway is weakly activated at the same time that antoeher is strongly activated, then both pathways show LTP

by spreading potential over many weakly activated pathways, associativity can increase the chances of the simultaneous pre and postsynaptic firing, thus enhancing learning (of the Hebbian sort)

Question 13

long-term depression

Answer 13

a mechanism of synaptic inhibition to counterbalance that of synaptic enhancement that is long-term potentiation;

elicited by low-frequency stimulation over a longer period as opposed to long-term potentiation;

an activity-dependent reduction in the efficacy of neuronal synapses lasting hours or longer following a long patterned stimulus;

can enhance LTP in neighboring synapses and can block formation of associations that don’t follow Hebbs rule

Question 14

behavioral LTP

Answer 14

a demonstrated change in synaptic efficacy similar to LTP that folows a natural learning experience

part of effort to directly link LTP and memory performance

done so far by 1) knocking out NDMA receptors and 2) examining synaptic connectivity before/after subjection to some situation, etc.

Question 15

glutamate

Answer 15

a neurotransmitter involved in the molecular mechanism behind LTP; connects to AMPA receptors which mediate normal synaptic transmission and NDMA, which plays a special role in LTP

Question 16

NDMA

Answer 16

glutamate receptor whose operation depends on the state of the postsynaptic cell. When the postsynaptic cell is resting, NMDA receptors are blocked. When the postsynaptic cell is depolarized, NMDA receptors allow calcium ions to pass through the receptor pore into the postsynaptic cell, triggering LTP.

Thus behaves like a molecular “AND” gate: only when glutamate is bound to these receptors AND the postsynaptic cell is depolarized is calcium allowed to flow into the postsynaptic cell to initiate LTP

accounts for the specificity (LTP is limited to active synapses where glutamate has been released) and the associative (can occur at synapses where a weak stimulus is not enough to depolarize the postsynaptic cell as long as a simultaneously occurring, nearby synapse is activated instead) properties of LTP.

Question 17

dendritic spines

Answer 17

part of learning-related changes in synaptic morphology;

small mushroom-shaped protrusions from dentritic branches that receive synaptic terminals from other neurons;

Question 18

four sources of morphological change of dendritic spine structure in response to LTP

Answer 18

1) increase in size of the spines
2) development of perforated synapses
3) complete split of a spine into two separate spines
4) increase in the number of spines by emerging from dendrite shaft

Question 19

medial temporal lobe

Answer 19

critically important in encoding and consolidating the sorts of memories that are accessible to consciousness and can thus be reported;

consists of the hippocampus and the surrounding rhinal and parahippocampal cortex - the amygdala sits in the anterior part of the medial temporal lobe but is not considered a memory region per se;

Question 20

hippocampus

Answer 20

page 336 (must I be this detailed?)

Question 21

HM

Answer 21

patient with bilateral removal of his temporal lobes on boths sides, including amygdala, entorhinal cortex, and about two-thirds of hippocampus, well studied because his cognitive deficits are very selective;

mainly impaired in learning new information rather than in retrieving well-established memories; deficit is mostly domain-general; long-term procedural memory and working memory is intact

Question 22

anterograde amnesia

Answer 22

pathological memory problems that primarily affects memories of events that occur after the onset of some brain order; a problem establishing new memories

Question 23

retrograde amnesia

Answer 23

pathology affecting memory of events that occur after onset of some brain disorder

Question 24

digit-span task

Answer 24

experimenter reads a list of digits (numbers) and the patient or subject repeats them back immediately; number of digits is increased until the individual starts making errors; the number of digits repeated sans error is the digit span and normally 7-9 digits

Question 25

mirror drawing task

Answer 25

a task that involves tracing geometric figures that can only be seen via a mirror; procedural learning can be demonstrated by observing reductions in mistakes during the task over time that persist normally over time

Question 26

implications of HM’s case

Answer 26

• medial temporal lobes are needed memory functions, but not for perceptual, intellectual and executive functions
• and not for memories expressed through performance, such as motor and other skills
• needed for remembering recent events but not for the memory of remote events
• needed for explicit memory functions regardless of the sensory modality involved
• needed for transferring events and facts into long-term memory storage, but not for the current retention of information “online”

Question 27

working memory

Answer 27

maintenance and manipulation of information for brief periods of time; subsumes short term memory

Question 28

long-term memory

Answer 28

acquisition and recovery of information over longer periods

Question 29

declarative memory

Answer 29

remembering of events and facts - that is, of things that can be declared. ALso called explicit memory.

Question 30

nondeclarative memory

Answer 30

memories expressed through performance. Implicit memory.

Question 31

episodic memory

Answer 31

declarative memory of personal experiences

Question 32

semantic memory

Answer 32

general knowledge about the world (declarative)

Question 33

priming

Answer 33

nondeclarative memory involving faciliated processing of a particular stimulus based on previous encounters w/ the same or a related stimulus

Question 34

skill learning

Answer 34

gradual improvement in performance as a result of practicing a motor or cognitive tsak (nondeclarative)

Question 35

conditioning

Answer 35

formation of simple associations b/t different stimuli and b/t stimuli and responses

Question 36

word list free recall studies

Answer 36

way of studying how people remember terms from sequentially ordered lists

Question 37

recency effect

Answer 37

normally the last few words of the list are recalled better than the rest of the list, occurs probably because the last few words are still active in working memory; other words must ben in long-term memory

Question 38

variables that differentialy affect working/long-term memory

Answer 38

• a 30-second distraction b/t the last word on the list and recall test eliminates recency effect (thus working memory)
• slower presentation rate enchances recall of most of the list but does not alter the recency effect (improves long-term, doesn’t affect short term)
• medial temporal lobe lesions impair long term memory w/o affecting the recency effect (working memory)

Question 39

stem completion task

Answer 39

They asked amnesic participants to read a list of words several times and then tested them on recall, recognition, fragmented words or a WSC task (the first few initial letters were presented);

Declarative version: complete stems w/ studied word.

Implicit version: complete stems w/ first word that comes to mind. Priming is measured as the increase in the probability of completing stems w target words when these were previously encountered in the experiment as opposed those that weren’t.

Yields clear dissociation: amnesiacs impaired in declarative version of task, but not in the nondeclarative version.

Question 40

case of MS

Answer 40

had right occipital regions removed including priamry and much of secondary visual cortex removed and so blind in left visual field.

Showed no priming effect, but performed normally on explicit recognition test (on stem completion task).

Showed occipital lobe is critical for some forms of nondeclarative memory.

Question 41

encoding

Answer 41

creation of memory traces

Question 42

storage

Answer 42

persistence of memory traces over time

Question 43

retrieval

Answer 43

ability to access memory traces

Question 44

consolidation

Answer 44

progressive stabilization of long-term memory that follows the initial encoding of memory traces.

Demonstrated as a significant phenomenon because an amnesic agent impairs memory to a greater extent during an early time window rather than during a later.

Question 45

Synaptic consolidation

Answer 45

changes in gene expression, protein synthesis, and synaptic plasticity that allow the persistence of memory traces at the cellular level

disruptible by admistration of protein-synthesis inhibitors. takes about an hour.

Question 46

protein-synthesis inhibitors

Answer 46

They block changes in synaptic morphology but not perceptual and motor processes required for task performance; said to disrupt synaptic consolidation

disrupts when administered during 1st hour after training, but not thereafter - showing that consolidation takes about that much time.

Question 47

system consolidation

Answer 47

can take days, months, years and involves a reorganization of the brain regions that support a given memory;

occurs when a particular brain region that was necessary for post-encoding memory performance is no longer required OR when it can be demonstrated that another brain region is now needed to preserve the memory

though occurs for both declarative and nondeclarative memory, used mostly to refer to changes in the role of the medial temporal lobe regions in declarative memory

Question 48

Ribot’s law

Answer 48

brain damage affects recent memories to a greater extent than remote memories

Question 49

standard consolidation theory

Answer 49

theory that the hippocampus rapidly encodes an integrated representation of an event or concept, which is then slowly transferred to the cortex and eventually becomes independent of the hippocampus

indirect connections via the hippocampus are gradually replaced by direct connections among the neocortical neurons relevant to the memory; when consolidation is complete, cortical neurons hold the unified memory and connections w/ the hippocampus are no longer necessary;

explains why medial temporal lesions are so disastrous: nonconsolidated memories can only be accessed through the hippocampus;

asserts that consolidation happens when a memory is repeatedly reactivated - which can happen during conscious remembering or during sleep;

memory reactivation leads to teh creation of direct connections among distributed cortical traces.

Question 50

standard consolidation theory justification

Answer 50

memory traces are distributed across several regions, each of which processed different aspects of the original event; because memory traces are distributed it seems critical to have a region in the brain - such as the hippocampus and related temporal lobe structures - that holds a unified representation of the whole event, along with pointers to the locations of the distributed traces

Question 51

standard consolidation theory issues

Answer 51

1) in patiens w/ medial temporal lobe amnesia, retrograde amnesia for autobiographical memory is quite extensive, sometimes spanning the entire life of the individual; interpreted in context of standard theory, the consolidation rpocess may take more than 40 years: as long as the human lifespan througout most of history
2) presumes, along w/ the multiple trace theory that hippocampal (declarative?) storage is fast and cortical storage is very slow; in the standard theory these reactivations lead to a transfer of declarative memories; in muliple trace theory, they lead to the creation of separate semantic traces in teh cortex w/ the further idea that hippocampal traces are always necessary for episodic memory

Question 52

multiple-trace theory

Answer 52

alternative to standard consolidation theory that asserts that episodic memories, consolidated or otherwise, are always dependent on the hippocampus;

describes temporal gradient observed in amnesic patients as resulting not from transfer to the cortex but to the number of traces stored in the hippocampus: each time a memory is activated, a new trace for the memory is stored in the hippocampus;

however also makes the claim that when hippocampal damage is complete, the gradient for episodic memories should be flat or nonexistent.

As for semantic memories, theory postualts that they are gradually extracted from repeated episodes and are stored in the cortex independely of the hippocampus.

Question 53

interleaved learning

Answer 53

possibility suggested by a computational memory omodel of James McClelland that the cortex acquires information such that a particular item is not learned all at once, but through a series of presentations intermixed w/ exposure to other examples of the same general domain, allowing the the cortex to extract invariant relationships among concepts and to form the categorical organization that characterizes semantic knowledge. Simulations show that if one attempts to incorporate new info in a semantic network too fast, the structure of the whol thing destabilizes (catastrophic interference).

In this scenario, hippocampus and neocortex are complementary learning systems: one rapidly acquires novel information and the other slowly learns invariant relationships among various pertinent bodies of information to weave long-lasting and usefully accessible memories.