Memory

What is learning?

• acquisition of new information

What is memory?

• outcome of learning

What underlies learning and memory in the nervous system?

• cellular and circuitry changes

What characteristics differentiate types of memory? (5)

• storing different types of information

• operating over different time courses

• having different storage capacities

• being conscious or not

• relying on different brain circuits

What are the three stages of memory processing?

• Encoding
• Storage
• Retrieval

What does encoding include?

• acquisition
• consolidation

What is storage in memory?

• retention of memory traces

What is retrieval in memory?

• access to stored memory traces

What is amnesia?

• memory loss, mostly due to brain damage

What is retrograde amnesia?

• loss of memory before the brain lesion

What does Ribot’s law state?

• retrograde amnesia is greatest for the most recent memories (after brain lesion, but also after electroconvulsive therapy or severe head trauma)

What is anterograde amnesia?

• loss of memory after the brain lesion (problems with encoding or consolidation)

What was H.M.’s memory deficit?

• severe anterograde amnesia after bilateral hippocampus lesion

What’s a single dissociation?

• damage to brain area X impairs task A but not task B

• brain area X and task A are associated, whereas brain area X and task B are dissociated → interpretation problematic

What’s a double dissociation?

• damage to area A impairs memory type A but not type B, while damage to area B impairs memory type B but not type A → strongest evidence for distinct systems, indicated that two cognitive operations are independent

What are the two main types of memory?

• long-term memory

• short-term memory/working memory/sensory memory

Which 2 subtypes does short-term memory have?

• sensory memory

• working memory

Which 2 subtypes does long-term memory have?

• explicit memory (declarative memory)

• implicit memory (nondeclarative memory)

Which 2 subtypes can explicit memory be divided into?

• episodic memory (events) → specific personal experiences from particular time and place

• semantic memory (facts) → world knowledge, object knowledge, language knowledge, conceptual priming

Which brain structures are responsible for explicit (episodic and semantic) memory?

• medial temporal lobe

• middle diencephalon

• neocortex

Which 4 subtypes can implicit memory be divided into?

• procedural memory

• perceptual representation system

• classical conditioning

• nonassociative learning

What’s procedural memory and where does it take place?

• skills (motor and cognitive)

• basal ganglia, skeletal muscle

What is the perceptual representation system and where is it located?

• perceptual priming

• perceptual and association neocortex

What is classical conditioning and where does it take place?

• conditioned responses between two stimuli

• cerebellum

What is nonassociative learning and where does it take place?

• habituation, sensitization

• reflex pathways

How is sensory memory characterized in terms of time course, capacity, conscious awareness and mechanism of loss?

• time course: milliseconds to seconds

• capacity: high

• conscious awareness: no

• mechanism of loss: primarily decay

How is short-term and working memory characterized in terms of time course, capacity, conscious awareness and mechanism of loss?

• time course: seconds to minutes

• capacity: limited (7 +-2 items)

• conscious awareness: yes

• mechanism of loss: interference and decay

How is long-term nondeclarative memory characterized in terms of time course, capacity, conscious awareness and mechanism of loss?

• time course: minutes to years

• capacity: high

• conscious awareness: no

• mechanism of loss: primarily interference

How is long-term declarative memory characterized in terms of time course, capacity, conscious awareness and mechanism of loss?

• time course: minutes to years

• capacity: high

• conscious awareness: yes

• mechanism of loss: primarily interference

How are the processing stages and types of memory connected?

Which two subtypes of sensory memory are there?

• echoic memory (auditory)

• iconic memory (visual)

How is echoic memory characterized in terms of persistence, capacity and time course?

• persistence: unattended auditory information persists like an echo

• has high capacity and can be partially accessed when attended

• auditory sensory memory trace can last up to 10 seconds (ERP mismatch negativity)

How is iconic memory characterized in terms of persistence, capacity and time course?

• Persistence: unattended visual information persists like an “informational” afterimage

• Has high capacity and can be partially accessed when attended (partial report)

• Visual sensory memory trace lasts only 300–500 ms (partial report advantage)

How many items can most people report from a visual scene when tested and what does that imply?

• ~4 items

• at odds with our subjective experience of rich visual world

What’s the Sperling paradigm?

• researcher flashed 3 rows of 4 letters, then showed black screen

• participants were asked to give “whole report” of what they saw → on average: 4 letters → measures short-term memory (capacity limited)

• other condition: participants were played short tone (either high, medium or low)

• then asked to report letters → “partial report” of ~3-4 items, but from cued row → 9-12 items were available in brain → cue makes high-capacity memory trace accessible, revealing sensory memory

What’s the modal model and what does it say?

• by Atkinson & Shiffrin

• influential hierarchical, serial model of memory → basis for account of partial vs. whole report

• attention moves items from sensory to short-term memory

• rehearsal moves items from short-term to long-term memory

• information can be lost by decay or by interference

Why is the modal model debated?

• does information have to be encoded in short-term memory before being stored in long-term memory? → is it really serial?

• evidence against modal model from neuropsychological patients

What was recorded in a patient with long-term memory without short-term memory?

• patient K.F. (left parietooccipital damage)

• impaired verbal short-term memory (e.g. measures of digit, letter, and word span)

• normal declarative long-term memory (e.g. learning of ten words, 7 still remembered after two months)

→ single dissociation

What was recorded in a patient with short-term memory without long-term memory and what does that imply together with the results from patient K.F.?

• patient H.M. (bilateral hippocampus damage)

• preserved short-term memory (e.g. digit span)

• impaired declarative long-term memory (anterograde amnesia)

→ double dissociation

How does working memory compare to short-term memory?

• working memory = extended concept of short-term memory

• maintenance of information (e.g. remembering list of number)

• manipulation of information (e.g. summing list of numbers)

What does the Baddeley and Hitch working memory model say?

• central executive: role in executive control

• two subordinate short-term memory stores (rather tan one unitary one):

• phonological loop: rehearsal via acoustic code (e.g. of words, letters) instead of visual or semantic → verbal working memory

• visuospatial sketchpad: rehearsal via visual code → visuospatial working memory

• different brain circuits for two stores: verbal → left inferior frontal, spatial → right (fronto)parietooccipital

What characterizes nondeclarative long-term memory?

• not expressed verbally (cannot be declared), instead: previous experiences influence performance on tasks that don’t require intentional recollection of these experiences

• intact in H.M. → doesn’t rely on medial temporal lobe, but on other brain structures

What’s the serial reaction time task and for which type of memory is it relevant?

• for procedural memory: motor skill learning

• press corresponding button as fast as possible upon stimulus presentation

• structured/repeated (s) or random (r) sequence

What leads to faster responses on the serial reaction time task?

• generally, practice

• faster responses with structured sequence, even without awareness of structure

• intact in anterograde amnesia (e.g. H.M.)

Which network is involved in the early learning phase in the serial reaction time task?

• motor skill learning network (premotor, SMA, basal ganglia, cerebellum, parietal cortex)

How can the brain activity in the later learning phases be described?

• reduced activity in motor skill learning network (reduced demands for error correction)

What is priming?

• change in processing of stimulus following prior exposure to that or related stimulus

• in absence of intentional memory strategies

What are the three types of priming?

1. Perceptual Priming

2a. Conceptual Priming

2b. Semantic Priming

What’s perceptual priming?

• full or partial repetition of stimulus can prime form of objects and words

• example: word-fragment completion task

• specific to sensory modality of learning phase → relies on sensory cortices

• can last hours to months

Does perceptual priming work in H.M. and what does that imply?

• intact in anterograde amnesia (H.M.) → patients show priming without any memory of ever having encountered stimuli before

• double dissociation: patient M.S. (right occipital lobe damage) with intact episodic memory but no visual priming

What’s conceptual priming?

• test cue is conceptually/semantically related to prime

• example: category-association test (generate words in response to cue)

What’s semantic priming?

• prime and target are different stimuli (words) from same category

• example: simple speeded decisions on words are faster for semantically related prime-target pairs

• assumes that semantic memory is organized in associative networks

How do conceptual and semantic priming compare to perceptual priming?

• do not last as long as perceptual priming and are independent of sensory modality

Does conceptual and semantic priming work in H.M. and what does that imply?

• intact in anterograde amnesia (H.M.) → do not rely on medial temporal

Which brain areas do conceptual and semantic priming rely on?

• on anterior lateral temporal and inferior frontal (Broca’s) regions

What characterizes declarative long-term memory?

• can be expressed verbally (”declared”), is consciously accessible

• impaired in H.M. → relies on medial temporal lobe

How are encoding and storage affected by damage to the medial temporal lobe (MTL)?

• encoding: impaired by MTL damage → MTL key for formation of new long-term memories

• storage: less affected by MTL damage → MTL not key for storage of long-term memories

How was the hippocampus lesioned in patient R.B. with anterograde amnesia and only mild retrograde amnesia?

• seemingly intact hippocampi

• but selective lesions to CA1 region of hippocampi with CA1 pyramidal cells

How do the brain areas for episodic and semantic memory differ?

• encoding of episodic memories: hippocampus CA1 region in MTL

• semantic memory loss after lesions of lateral cortex of anterior temporal lobe that don’t involve hippocampus

What happens in semantic dementia?

• isolated retrograde amnesia

• anterior temporal lobe damage: loss of semantic knowledge → may be involved either in storage or retrieval of semantic knowledge

• episodic memory is intact, can learn new episodic information

Which stage of memory processing involves which brain area?

• encoding: involves MTL (hippocampus)

• storage: not necessarily MTL, primarily neocortex

• retrieval: involves MTL (hippocampus)

What’s the subsequent memory paradigm and which stage of memory processing does it concern?

• measure brain activity during encoding of items

• test memory for those items later outside of scanner

• analyze imaging data collected during encoding as function of remembered vs. forgotten items

• greater MTL activity for remembered vs. forgotten items during encoding

What’s the difference between recollection and familiarity-based recognition?

• episodic recollection: correctly identifying item as encountered before (incl. context, → what happened where, when and with whom)

• familiarity-based (non-episodic) recognition: merely identifying item as being familiar

How do you measure hippocampus activity during retrieval of recollection or familiarity and what are the results of these measurements?

• encoding outside scanner, scan during retrieval

• hippocampus only for correct episodic recollection but not for familiarity-based recognition

How do you measure hippocampus activity during encoding of recollection or familiarity and what are the results of these measurements?

• = subsequent memory paradigm

• hippocampus only for correct episodic recollection

• familiarity-based recognition in perirhinal cortex

Where are the perirhinal cortex and the hippocampus located?

Which brain area does retrieval reactivate?

• during encoding of sounds and pictures, high-level, modality-specific sensory areas provide input to hippocampus

• during retrieval, similar sensory areas are activated

• suggests that information stored in long-term memory is retrieved by reactivation of neocortical areas

How can you induce false memories?

• e.g. editing childhood photographs into hot-air balloon ride

• 50% of participants actively created false childhood memories

How do false memories compare to true memories?

• false memories often lack sensory detail

How does the retrieval of true vs. false memories differ?

• only true memories: hippocampus + sensory cortex

• false memories: frontoparietal areas (top-down mechanisms)

Which brain structure does initial storage involve and what happens after?

• MTL (hippocampus), e.g. impaired in H.M.

• mechanics of subsequent slower consolidation process = controversial

What’s the standard theory of consolidation?

• neocortex is key

• initially, hippocampus binds event information distributed across neocortex

• next, information is slowly transferred to neocortex

• repeated memory retrieval creates intracortical connections, hippocampus is unnecessary

• Ribot’s law: more recent events have not completed the consolidation process yet

What’s the multiple trace theory?

• hippocampus remains key

• episodic memory relies on hippocampus for retrieval

• repeated memory retrieval creates new memory traces involving hippocampus

• Ribot’s law: remote events have more traces as they have been retrieved more often

What’s Hebb’s law?

• cells that fire together, wire together

What’s Hebbian learning?

• strengthening of synaptic connections when weak and strong input act on neuron at same time

Which studies supported both Hebb’s law and Hebbian learning?

• studies on long-term potentiation (LTP)

What’s long-term potentiation?

• after high-frequency burst to pathway 1, post-synaptic neuron exhibits stronger responses to pathway 1

• specific to stimulated change (no response to pathway 2)

• increases sensitivity is long-lasting → LTP

• long-term depression happens with very low-frequency bursts → weakening of synapses

What are properties of LTP?

• can happen after one burst (”one-shot learning” possible) and can last for weeks

• associative: weak inputs are potentiated when co-occurring at the same target neuron with strong inputs (and inputs become associated)