Psyc 251 - long-term memory

problem

how to acquire information for experience, maintain it over time, and use it when relevant to guid behaviour and plan future actions

importance

to remember past experience, ability to grow and change over time, learn from experiences in world

challenge

out of all experiences, what to remember, and how to retrieve it when needed

memory involves multiple …

processes, types, systems, tasks. requires a physical change in nervous system and is pervasive

similarities between computer and human memory

a common underlying representation (binary digits vs number and strength of synapses), short-term memories that require active maintenance (RAM, cache, registers vs sensory, short-term and working memory, require active firing of neurons to remain), long-term memories that can be passively stores (hard rives vs long-term memory)

differences between computer and human memory

organization of storage and processing (memory storage is physically separate form processing vs location of memory storage and processing coincide), interpretation of representations (a pattern can have the same interpolation wherever it occurs vs interpretation of a synaptic weight depends on its location in nervous system), access to memories (memory is accessed based on its address vs memory is accessed based on its content)

encoding

initial creation of memory traces in brain from incoming information

consolidation

continued organization and stabilization of memory traces over time

storage

retention of memory traces over time

retrieval

accessing/using stored information from memory traces

reconsolidation

possible reorganization and destabilization of memory traces after retrieval

dissociating short-term and long-term memory tasks

short term: memory span, hear three words and immediately recall in same order. long-term: list learning, hear 10 words, repeat until all 10 are recalled in any order

patient K.F.

damage to left temporoparietal cortex

patient H.M.

damage to bilateral medial temporal lobes

dissociation

performance differs across two tasks

partial damage argument

there is one system for both short and long-term memory. the short-term task is harder than the long-term task. so when the memory system is damaged, the short term task suffers more than long term task

compensation argument

there is one system for both short and long-term memory. the short-term task is harder than the long-term task. when this system is completely damaged, the brain can compensate for the long-term task but not the short-term

double dissociation

provides strong evidence for separable systems that depend on different brain regions and distinct cognitive processes

how many words on average can a person remember in the memory span task?

7

how many words on average does a person have in their vocab?

20,000

short-term memory

timescale: seconds, capacity: extremely limited, neural basis: sustained activation of neurons

long-term memory

timescale: minutes, hours, days, years, capacity: massive, neural basis: number and strength of synapses

explicit and implicit task double dissociation

patient M.S: damage to right occipital lobe, performed bad on perceptual identification but good on word recognition. amnesia patients (Korskoffs syndrome due to severe alcoholism and epilepsy) had good perceptual identification and bad word recognition. provides evidence of implicit and explicit memory being diffenrt processes in different brain areas

implicit memory

non-declarative, independent of conscious awareness, procedural, conditioning, non associative or priming. eg. riding a bike, skilled motor sequences

similarities between implicit and explicit memory (LTM)

timescale for both: minutes, hours, days years. capacity for both: massive. neural basis: number and strength of synapses

explicit memory

declarative, available to conscious awareness, semantic or episodic. eg. facts, words in adult vocabulary

non-associative memory (implicit)

a change in réponse to an unchanging stimulus

habituation

reduced response to an unchanging stimulus (considered LTM)

sensitization

increased response to an unchanging stimulus (considered LTM)

first evidence of neural basis of memory

sea slug Aplysia studied because of simple nervous system and big neruons. Eric Kandel - 2000 Nobel prize

presynaptic depression

habituation, same action potential, reduced neurotransmitter realize, smaller EPSP

presynaptic facilitation

sensitization, same action potential, increased neurotransmitter release, larger EPSP

habituation and sensitization short and long term changes

short term changes: lasts for minutes, changes in amount of neurotransmitter released. long-term changes: lasts for hours, days, weeks, changes in number of synapses

fear conditioning with electrophysiological testing

after testing, EPSP to tone increases in lateral nucleus of amygdala due to pairing with the shock

motor skill learning: motor adaptation and motor sequence learning

motor adaptation: cerebellar loops. motor sequence learning: cortico-basal ganglia-thalamocortical loops

motor adaptation and cerebellar lesion

throwing darts, prism glasses shift visual fields. control group are able to adapt to prism glasses and to taking them off. cerebellar lesion participants fail to adapt to distortion, perform the same throughout

cerebellum

uses forward model to predict results of motor commands. uses differences between actual and predicted results for online error correction and motor learning

basal ganglia and reinforcement learning

select action expected to lead to maximum reward, perform action, compare action reward to expected reward (prediction error = actual reward - predicted reward), use prediction error to update expectation, repeat until desired action is reached.

basal ganglia reinforcement learning and SNc

dopamine signal form substantia nigra pars compacta represents prediction error. larger response = better than expected, smaller response = worse than expected. dopamine excites direct pathway (via D1 receptors) and inhibits indirect pathway (via D2 receptors)

benefits of learning an instrument

larger grey matter volume on both sides of cerebellum, better cerebellar-hippocampal functional connectivity, better cognitive and motor function in older adulthood

priming

change in stimulus processing due to prior exposure to same or related stimuli without conscious awareness

perpetual priming Warrington and Weiskrantz

participants shown goblin figures (fragmented pictures), Karsakoff syndrome patients showed improvement in recognition day to day, despite not remembering the previous days training (required fewer frames to recognize object)

semantic priming

semantic priming task: lexical decision: word or non-word. in both long and short intervals, participants were faster for related words than unrelated words = semantic priming effect. N400 component (reflects meaning and language comprehension) is modulated by semantic priming

perceptual and conceptual/semantic priming

priming depends on region of cortex processing relevant representations. perceptual priming: sensory cortices (eg. occipital lobe for vision). conceptual/semantic priming: unimodal and multimodal association cortices (eg. anterior temporal, inferior partial, prefrontal cortex)

semantic memory

memory for concrete word meanings activates areas of cortex involved in relevant processing, distributed across cortex

semantic memory actions

motor cortex/somatosensory cortex (eg. throw or run)

semantic memory sounds

auditory cortex (eg. sound associated words)

Semitic memory colours and movements

ventral visual stream (occipital/temporal cortex)

sensory/functional theory

organization of semantic representations is based on relevant sensory and motor features (eg. action words activate region of primary motor cortex for specific body part, lick - face, pick - arm)

domain-specific theory

organization of semantic representations is based on semantic categories (eg. fruits and vegetables, animate living things, nonliving things, conspecifics - mom, dad, mailman). this comes from studies of individuals with brain damage, deficits in different domains (picture naming studies)

sensory/functional vs domain-specific theory

perhaps both right: fMRI data from silent naming of tools and animals support domain-specific theory. tools are strongly associated with actions supports sensory/fucntional theory. categories often correlate with sensory/functional distinctions.

encoding of episodic memory (explicit)

hippocampus and related structures form indices (pointers) to bind cortical representations

retrieval of episodic memory

hippocampus and related structures use indices (pointers) to reinstate cortical representations

fornix

axons that connect hippocampus to other parts of brain

cognitive map theory

memory for spatial relationships in enviormnet

place cells

fire when animal is in a particular location. 2014 Nobel prize: O'Keefe, Moser and Moser. important for memory to know where something happened

relational memory theory

memory for associations in general. odor association task: participants with lesion to fornix (cuts off hippocampus from cortex) can't see relationships across pairs. suggest that medial temporal lobes are important for association between facts.

role of perirhinal cortex

binding features of objects

parahippocampal cortex

encoding spatial layout

hippocampus

encoding relationships more generally

hebbian learning

"neurons that fire together wire together" when presynaptic action potential leads to postysynaptic action potential, connection is strengthened (next time it fires, more likely postsynaptic AP will fire too) (eg. copying drawings after seeing them in study phase, drawings not perfect)

long-term potentiation (LTP)

increase in synaptic strength, exhibits necessary properties for Hebbain learning, found in hippocampus (and other brain regions)

early LTP

increased presynaptic release of neurotransmitter, increased number of postsynaptic receptors

late LTP

increased number of dendritic spines of synapses

what is wrong with learning based solely on LTP?

if synapses only strengthen, neural firing will grow out of control (positive feedback loop)

long-term depression (LTD)

"neurons that fire apart wire apart" when presynaptic AP does not lead to postsynaptic AP, connection is weakened. reduction in neurotransmitter released, number of receptors, and number of synapses

retrieval of episodic memories is called …

reconstruction

episodic retrieval / reconstruction is based on:

memory trace, genes, past experience, internal state, environmental context

episodic retrieval can be inaccurate for reasons including:

semantic relatedness, cultural experience, source misattributions, pragmatic inferences, misleading post-event information

results of Deese, Roediger and McDermott (DRM) paradigm

related lures reported almost as often as words actually on the list, high confidence in accuracy for both words on list and lure words, reports of specifically remembering presentation of lures, happens even if you know about the effect

anterograde amnesia

inability to form new episodic memories

retrograde amnesia

inability to remember things that happened before incident/surgery

Patient H.M.

removal of bilateral medial temporal lobes (to treat epilepsy), resulted in severe anterograde amnesia and temporally-graded retrograde amnesia. unable to from new LTM after surgery and unable to recall existing LTMs form just before surgery.

consolidation related to representations

new memories depend on representations in cortex and links from hippocampus. over time, reactivation due to retrieval and really during sleep reduce dependence on hippocampus. old memories depend on representations and links in cortex (explains H.M. amnesia)

why have two memory systems - hippocampus

learns rapidly (single trail learning), creates distinct memories for each event/instance, more important for episodic memories

why have two memory systems - cortex

learns slowly, extracts generalities across events/instances, more important for semantic memories

is consolidation a permanent process?

old idea: once a memory is formed it is more or less permanent. new idea: reconsolidating - when a memory is retrieved it is reformed and is once aging subject to interference

reconsolidating - Nadar et al fear conditioning in rats

rat injected with anisomycin, which blocks memory consolidation in amygdala. rat has no memory of tone + shock paring when anisomycin is injected as rat freezes to tone (during reconsolidating, memory is blocked)

importance of reconsolidation

may need to make memories available again, allows them o change based on later experiences. recently, reconsolidating has been demonstrated in many LTM systems across many organisms, including humans (eg. changing traumatic memories)