LEARNING AND MEMORY

medial temporal lobe amnesia

patients with a profile of mnemonic deficits similar to those of H.M., with preserved intellectual functioning, and with evidence of medial temporal lobe damage are said to suffer from this -symptom: difficulty in forming explicit longterm memories while retaining ability to form implicit long term memories

anterograde amnesia

forward-acting amnesia

rhinal cortex and memory

(located in medial temporal lobe) -object recognition, houses memory for what things ARE -damage produces deficits in terms of person not recognizing or being able to name objects they see in their environment

block-tapping memory span test

-H.M. had global amnesia (amnesia for info presented in all sensory modalities) -this test demonstrated that his amnesia was not restricted to verbal material. -9 blocks were spread on a board in front of him and he was asked to watch a neuropsychologist touch a sequence of them and then he had to repeat the same sequence of touches -block-tapping span of 5 blocks which is within normal range, but he couldn't learn to touch 6 blocks even when sequence was repeated 12 times

2 characteristics of LTP

-LTP can last for a long time (for several months after multiple stimulations) -LTP develops only if the firing of the presynaptic neuron is followed by the firing of the postsynaptic neuron (does not develop when presynaptic neuron fires and postsynaptic does not or vice versa)

cells in hippocampus -found where specifically -what's unique about them

pyramidal cells -in CA1 and CA3 subfields -action potential can flux back thru dendrites (instead of just going in 1 direction)

H.M. case

-before surgery: for 11 years, suffered an average of 1 generalized seizure a week and many partial seizures every day, despite massive doses of anticonvulsant meds -decision was made to perform a BILATERAL MEDIAL TEMPORAL LOBECTOMY (the removal of the medial portions of both temporal lobes, including most of the hippocampus, amygdala, and adjacent cortex -generalized seizures were all but eliminated and partial seizures only 1 or 2 a day -post surgery: still a well-adjusted person. IQ went from 104 to 118 -post-surgery memory: mild retrograde amnesia for events that occurred 2 years before his surgery but memories for remote events from childhood were reasonably normal -short term anterograde remained normal. his digit span was 6 -TOTAL INABILITY to form new long term memories (anterograde amnesia)

digit span test + 1

-demonstrated H.M.'s inability to form certain LTM -classic test of verbal LTM -H.M. was asked to repeat 5 digits that were read to him at 1 second intervals. -he repeated it correctly -next trial: same 5 digits in same sequence + 1 new digit at the end -this 6 number sequence was presented a few times til he got it right -after 25 trials, H.M. had not managed to repeat the 8 number sequence. normal subjects repeat 15 digits after 25 trials

mirror drawing test

-first indication that H.M.'s anterograde amnesia did not involve all long term memories -task: draw a line within the boundaries of a star-shaped target by watching his hand in a mirror -he was asked to trace the star 10 times on each of 3 consecutive days and the number of times he went outside the boundaries on each trial was recorded -his performance improved over 3 days, indicating a retention of the task -despite improved performance, he could not recall ever having seen the task before

LTP process starts at presynaptic membrane...

-glutamate is released during action potential, onto pyramidal cells of hippocampus -glutamate binds to receptor on calcium channel -channel opens (doesn't necessarily result in calcium influx into membrane) -calcium does NOT come in b/c magnesium ion is typically blocking the calcium channel -if cell is depolarizing and experiencing action potential, then the depolarization throws off the magnesium ion which typically blocks the channel (if postsynaptic cell isn't depolarized and experiencing action potential, nothing happens)

hypotheses on which part of damaged brain is responsible for the amnesia in korsakoffs patients

-mammillary bodies of hypothalamus: based on several postmortem exams. BUT later cases revealed patients with NO damage here -mediodorsal nuclei of thalamus: in all cases, there was damage here. however, it's unlikely that the memory deficits are attributable to the damage of any single diencephalic structure

incomplete pictures test

-mirror drawing and rotary pursuit suggested that sensorimotor tasks were the exception to H.M.'s inability to form LTM -but the incomplete pictures test challenged this by showing that he could also form LTM for incomplete pictures test: a nonsensorimotor test of memory that employs 5 sets of fragmented drawings. each set contains drawings of the same 20 objects, but the sets differ in their degree of sketchiness: set 1 contains the most fragmented drawings and set 5 contains the complete drawings -subject is asked to identify the 20 objects from the sketchiest set (set 1) and then set 2 and so on until all objects are identified -after an hour, H.M.'s performance improved but he could not recall previously performing the task

NMDA receptor

-prominent at synapses where LTP is commonly studied -it's a receptor for glutamate -does not respond maximally unless 2 events occur simultaneously (glutamate must bind to it and postsynaptic neuron must already by partially depolarized)

configural association theory

-proposes that the hippocampus is involved in retaining the behavioral significance of combinations of stimuli in our environment (why you jump back onto sidewalk if car comes toward you) -w/out hippocampus, it's predicted that you wouldn't understand the behavioral significance of jumping out of the way being necessary for survival -damaged hippocampus in animals after using stimuli associated w/ fearful stimuli like predators. once damaged, animals would not respond appropriately (just sit instead of hide)

hippocampus and memory

-spatial location and explicit memory consolidation -helps create engrams

rotary-pursuit test

-test: subject tries to keep tip of a stylus in contact with a target that rotates on a revolving turntable -found that H.M.'s performance on rotary-pursuit test improved significantly over 9 daily practice sessions, despite fact that H.M. claimed each day that he'd never seen the pursuit rotor before -his improved performance was retained over a 7 day retention interval

shortcomings of cognitive map theory

-the firing of place cells (neurons that respond only when a subject is in a specific location) has been found to depend on more than spatial location; also depends on recent or pending behavior in their place fields -hippocampal damage sometimes impairs the performance of tasks that have no obvious spatial component -the hippocampus is a large, complex structure, and thus unlikely to act as a unit with a single function. the functions of each part of the hippocampus need to be addressed

cerebellum

-thought to participate in the storage of memories of learned sensorimotor skills thru its various neuroplastic mechanisms -its role in pavlovian conditioning of eye-blink response of rabbits has been investigated

memory and amygdala

-thought to play a special role in memory for the EMOTIONAL significance of experiences -rats w/ amygdalar lesions don't respond with fear to a neutral stimulus that has previously been followed by electric foot shock -little evidence that amygdala stores memories; appears to be involved in strengthening emotionally significant memories stored in other structures

striatum

-thought to store memories for consistent relationships b/w stimuli and responses--the types of memories that develop incrementally over many trials (sometimes called habit formation) -parkinson's patients w/ damage her could not solve a probabilistic discrimination problem

Pavlovian conditioning

H.M. learned an eye-blink pavlovian conditioning task, albeit at a retarded rate -a tone was sounded just before a puff of air was administered to his eye; these trials were administered until the tone alone elicited the blink. -2 years later, he retained this conditioned response almost perfectly, although he had no conscious recollection of the training

korsakoff's syndrome

a disorder of memory that is common in people who have consumed large amounts of alcohol. -disorder is largely attributable to brain damage associated with the thiamine deficiency that often accompanies heavy alcohol consumption -in advanced stages: characterized by a variety of sensory and motor problems, extreme confusion, personality changes, and a risk of death from liver, gastrointestinal, or heart disorders -postmortem exams typically reveal lesions to the MEDIAL DIENCEPHALON (the medial thalamus and medial hypothalamus) and diffuse damage to several other brain structures, most notably the neocortex, hippocampus and cerebellum

long-term potentiation (LTP)

a facilitation of synaptic transmission following high-frequency electrical stimulation applied to presynaptic neurons

how to get a postsynaptic neuron to depolarize

a lot of input coming in at one synapse (while cell depolarizes, the depolarization works back thru dendrite and happens at same time that input is coming thru a dif synapse) -because cell is depolarized at same time that another synapse is depolarizing, we have a strengthening, so there's LTP on second synapse

N.A.

a man with medial diencephalic amnesia -stabbed thru right nostril w/ foil. pierced forebrain -initially, had extensive retrograde amnesia for 2 years prior to accident -2 1/2 years after accident, retrograde amnesia was only for 2 weeks prior to accident -at first, his day to day recall of events was very poor but his memory has continued to improve slowly -MRI revealed extensive medial diencephalic damage to the mediodorsal nuclei and mammillary bodies

multiple trace theory

alternative theory of memory consolidation -this theory is particularly compatible with the findings that gradients of retrograde amnesia are often very long -theory proposes that: the hippocampus and other structures involved in memory storage store memories for as long as they exist, not just during the period immediately after learning -when a conscious experience occurs, it is rapidly and sparsely encoded in a distributed fashion thru out the hippocampus and other involved structures -claims retained memories become progressively more resistant to disruption by hippocampal damage b/c each time a similar experience occurs or the original memory is recalled, a new engram (change in brain that stores memory) is established and linked to original engram, making the memory easier to recall and the original engram more difficult to disrupt

medial diencephalic amnesia

amnesia, such as Korsakoff's amnesia, associated with damage to the medial diencephalon -N.A.

prefrontal cortex

area of frontal cortex anterior to motor cortex -people w/ damage here often display no deficits on conventional memory tests -but Stuss and Alexander argue that diff parts of prefrontal cortex play diff roles in memory -2 episodic memory abilities are often lost by patients w/ large prefrontal lesions. often display both anterograde and retrograde deficits for TEMPORAL ORDER of events, even when they can remember the events themselves display deficits in WORKING MEMORY (ability to maintain relevant memories while a task is being completed) -patients w/ damage here often have difficulty performing tasks that involve a series of responses

retrograde amnesia

backward acting amnesia (events prior to surgery, in the past)

PKMzeta

believed to be responsible for LTP -over a long period of time, it seems to maintain the LTP that occurs by simultaneous firing of 2 neurons. -once activated, its presence seems to maintain the strength b/w the 2 neurons -if you inject rats w/ substance that inhibits this protein, rats will lose memory for events prior to protein blockage (up to 5 hrs of w/e it was that they learned, permanently removed)

key factor in LTP

co-occurrence of firing in pre and postsynaptic cells

explicit memory

conscious long-term memories

memory

deals with how changes in the brain (from experience) are stored and subsequently reactivated

learning

deals with how experience changes the brain

cerebellum and striatum

implicit memories of sensorimotor tasks thought to be housed here

2 HM tests that documented his severe deficits in long term memory

digit span test + 1 block-tapping memory test

LTP came about b/c of Hebb's hypothesis that...

enduring facilitations of synaptic transmission are the neural bases of learning and memory

semantic memories

explicit memories for general facts or info

episodic memories

explicit memories for the particular events (episodes) of one's life

implicit memory

long-term memories that are demonstrated by improved test performance without conscious awareness

glutamate

main excitatory neurotransmitter of the brain

the amnesia of korsakoff's is similar to... why?

medial temporal lobe amnesia in some respects because during early stages of korsakoffs, anterograde amnesia for explicit episodic memories is the most prominent symptom. however, as it progresses, severe retrograde amnesia which can extend to childhood develops.

5 HM tests that indicated that HM's brain was capable of storing long term memories but that H.M. had no conscious awareness of those memories

mirror-drawing test rotary-pursuit test incomplete-pictures test pavlovian conditioning repetition priming test

two types of explicit long-term memory

semantic and episodic

long-term memory

storage of new info once the person stops attending to it

short-term memory

storage of new information for brief periods of time while a person attends to it

standard consolidation theory

suggestion that memories are temporarily stored in the hippocampus until they can be transferred to a more stable cortical storage system -supported by several demonstrations that medial temporal lobe lesions produce temporally graded retrograde amnesia in experimental animals -came about b/c of the discovery that H.M. seemed to be suffering from a temporally graded retrograde amnesia. led Scoville and Milner to their theory

repetition priming test

test developed to assess implicit memory -incomplete pictures test is one example, but repetition priming tests that involve memory for words are more common -first participants are asked to examine a list of words. they are not asked to learn or remember anything. later they are shown a series of fragments of words from the original list and are asked to complete them.

memory and inferotemporal cortex

the cortex of the inferior temporal lobe -involved in visual perception of objects THUS it is thought to participate in storing memories of VISUAL PATTERNS

memory consolidation

the translation of short-term memories into long-term memories

cognitive map theory

theory of hippocampal function that acknowledges important role of hippocampus in spatial memory -most influential of the theories -claims: there are several systems in the brain that specialize in the memory for different kinds of information, and the specialization of the hippocampus is memory for spatial location -proposed that the hippocampus constructs and maintains allocentric maps of the external world from the sensory input it receives (allocentric: representation of space based on relations among external objects and landmarks -believes that hippocampus plays a role in episodic memory b/c the spatial context plays a critical role in acquiring and recalling the memory of any episode