PSY260 - 8. Episodic & Semantic Memory Flashcards
Sensory input carried by ascending activating systems
activates thalamus + hypothalamus - brain activates, ready to respond to stimulus
other regions activated simultaneously, but assess different aspects of stimulus (dangerous, want, like)
has yet to activate sensory cortex
info goes from hind brain to higher levels
cortical levels: explicit level
Sensory input carried by ascending activating systems
- Cholinergic, dopaminergic, adrenergic
- Activate limbic and cortical structures
- Responses modified by conditioning, implicit learning
Emotional + state-dependent regulation + memory
what we learn, how strong we learn depends on our emotion + physiological state
Emotional + state-dependent regulation + memory
- emotional context
- Physiological need
- Papez circuit, amygdala
- ANS
- Context relationships – hippocampus, amygdala
Emotional + state-dependent regulation + memory
fear conditioning
keeps us within an acceptable range ⇒ when we feel we start to think
Long term memory
- Semantic
* Episodic
Explicit
consciously accessible
we know we have
Implicit
Can the existence of the memory only be inferred from changes in behaviour or physiology?
Declarative
knowledge we can declare
non-declarative
-
Autobiographical
about ourselves
Semantic
general knowledge
memory for generic facts
Episodic
episode in our history
memory for specific episodes in life
Short versus long term memory
Working: temporary, things we are working on
Episodic: can also be temporary, but can be revisted, not recalled as an episode, brain has to reconstruct episode
Semantic: stored in multiple locations depending on how often they are needed
Short versus long term memory
Definitions vary and have changed over time Defined by: •Duration •Function •Underlying mechanism
Short versus long term memory
Working - short
Episodic - long
Semantic - long
Working Memory
Duration: seconds/minutes
Stored In: frontal cortex/TP
Represented As: sounds/meanings
Implemented As: neural activity
LTM
Duration: days/years
Stored In: hippocampus (⇒cortex)
Represented As: meanings
Implemented As: synaptic strengths
Basic Idea
event first buffered in WM, in prefrontal cortex
then replayed to hippocampus, involved in storing event in episodic memory
SM Processing - WM (PFC) - LTM (Hippocampus)
Baddeley’s model of working memory
WM refers to brain system that provides temporary storage + manipulation of info necessary for complex cognitive tasks - language comprehension, learning + reasoning
Baddeley’s model of working memory
i) central executive – controls attention, determines input we acquire - not needed, it disappears
ii) visuospatial sketch pad, manipulates visual representation
iii) the phonological loop: verbal representation
episodic buffer: creates temporary memory - sent to hippocampus if needed
Anders Ericsson and Walter Kintsch
view WM as component of long term memory
Miller (1956)
memory span of young adults around seven elements, regardless whether the elements were digits, letters, words
Chunking
span does depend on the category of chunks used (span around seven for digits, around six for letters + around five for words), and even on features of the chunks within a category
Working memory
involve 2 processes with diff neuroanatomical locations in frontal + parietal lobes.
selection operation retrieves most relevant item
updating operation changes focus of attention made
attentional focus
Updating attentional focus involve transient activation in caudal superior frontal sulcus + posterior parietal cortex increasing demands on selection selectively changes activation in the rostral superior frontal sulcus + posterior cingulate/precuneus.)
WORKING MEMORY (simplistic)
Even the concept of the number “2” (two) requires a long term memory. Concepts of “Larger than” and “smaller than” are relative, and are easier to define, but the symbolic meaning of 2 requires a rule. Also the meaning of 3 requires a symbolic meaning that places it as one unit greater than two units.
Working Memory
Involves frontal cortex + temporoparietal junction
Hippocampus
required to form new LTM
anterograde amnesia: damaged hippocampus, couldn’t store new episodes, severe loss of ability to form new episodic and semantic memory
integrates similar memories in WM
retrograde amnesia: forget episodes shortly before surgery
Hippocampus
determines whether experience important enough to put into LTM
remembers associations amongst context
features activate certain neurons in gyrus that distinguishes
gyrus: discriminates what’s happening now + what happened before - sent to CA3
Hippocampus
runs loop to cortex which strengthen memory of new cortex
when things are similar - we can modify knowledge
Hippocampus
Damage to hippocampus can eliminate LTM, but leave working memory intact
creates new memories, which are progressively consolidated into more permanent storage in cortex
Hippocampus
memories are stored in associations betw representations originating from different SM modalities in CA3
doesn’t store object + event representations
stores associations betw representations held elsewhere in cortex
Episodic Memory
must be tied to specific spatiotemporal contexts
in most/all mammals, used to represent spatial structure of local environment
environment representation stable over movements of animal
place cells fire when animal in particular place
Episodic Memory + Hippocampus
Animals store knowledge of differ spatial environs they encounter in hippocampal region
Diff environs stored as diff spatial contexts - probably stored in the parahippocampal cortex
Episodic Memory + Hippocampus
activity of place cells depend partly on perception + on active spatial context (Evidence from remapping of place cells when an animal moves to a new environment.)
•Episodic memories involve associations betw objects, actions + spatial contexts. (temporal contexts too
parahippocampal cortex
part of medial temporal cortex, adjacent to the hippocampus
Tulving
episodes are organized into sequences
Additional levels divide episodes into sequences
evidence in rats
sequences of hippocampal cell activity which occur during waking experience tend to be replayed during sleep (at much faster speed)
sequences of nonspatial stimuli also stored in hippocampus
evidence in humans
hippocampal activity during sequence encoding correlates with later retrieval success
Prefrontal Cortex
involved in process of encoding episodic memory
stimuli processed semantically subsequently better recalled
Semantic processing correlated with left PFC activity during encoding correlates with retrieval success
Encoding and recall of episodic memories
processes are mainly cortical
PFC/working memory is heavily involved
Encoding of episodic memories
Jensen and Lisman, 1996; Baddeley, 2000 model: episodic memories first buffered in WM before being replayed to hippocampus.
Encoding of episodic memories
Synapses in hippocampus strengthened by LTP - only occurs betw cells active within 100ms of one another Episodes often take tens of seconds to be experienced. So there must be a buffering mechanism.
LTM representations of objects
need to maintain representations of objects in LTM
have memories of many individuals: people, pets, cars
important difference betw categorizing an individual (‘it’s a dog!’) + recognizing it (‘it’s my dog Fido!’).
LTM representations of objects
individuals are stored in LTM in the perirhinal cortex
Perirhinal cortex involved in encoding + identification of familiar objects
Episodic
event is experienced as SM sequence
stored in WM as planned SM sequence
to store event in episodic memory, planned sequence replayed to hippocampus
hippocampus also stores event as sequence
Episodic
when retrieved, sequence is replayed from hippocampus + sequence plan is recreated in PFC, similar to plan created when event was experienced
Recall of episodic memories
Cue creation: creation of a memory cue
Retrieval: presentation of cue to hippocampus
Post-retrieval: monitoring of hippocampus’ response
Cue creation
PFC involved in the creation of memory cues.
Gershberg and Shimamura (1995): frontal patients generally worse at recall tasks than recognition tasks
Buckner et al. (1998): activity in PFC during recall correlates with retrieval effort rather than retrieval success
Cue creation
Memory cues originally created in PFC-based WM + communicated to hippocampus
echoes story about role of WM in episodic memory
creation
model of retrieval as rehearsal
retrieving a memory involves ‘reliving it’
hippocampus reactivates SM representations: Hippocampus projects to wide range of SM areas
model of retrieval as rehearsal
Damasio (1994): hippocampus is convergence zone
Burgess et al. (2000) fMRI study on humans: recall activates
parietal cortex (holding allocentric SM representations)
Ji and Wilson (2007) study on rats: fast replay of hippocampal place cell sequences during sleep coincided with replay of sequences of cells in visual cortex
The retrieval phase
retrieval operation is mainly control operation, which activates certain interfaces + deactivates others.
must open a connection from PFC to hippocampus, to communicate cue to hippocampus
The retrieval phase
retrieval operation must also establish a special retrieval mode, in which sensory cortices receive input from hippocampus rather than from world
The retrieval phase
Several ERP studies find short burst of activity in left parietal cortex occurring early in recall tasks
Summary
event is experienced as a SM sequence
stored in WM (in PFC) as planned SM sequence
planned sequence is replayed to hippocampus
Summary
hippocampus also stores event as a sequence
event is retrieved, sequence is replayed from hippocampus + sequence plan is recreated in PFC, similar to plan created when event was experienced
Mere exposure to info does not guarantee a memory
Mere repeated exposure to info not enough to guarantee memory
repetition of either verbal or visual info isn’t enough to ensure it’s being remembered
Memory is better for info that relates to prior knowledge
Only people going in the background info ahead of time remembered paragraph well
•With prep, students minds are better able to encode info presented in lecture
Deeper processing at encoding improves recognition later
- Deeper processing effect: preprocessing at encoding of new info improve ability to remember info later
- People remember words better if they’re forced to think about the Semantic content of words rather than simply asked to memorize them without efforts
- Brain areas activity during image condition particularly high left frontal cortex + left hippocampus
- Brains more active during the image trials
Memory retrieval is better when study and test conditions much
Transfer appropriate processing affect: retrieval more likely to be successful if cues available at recall similar to those available at encoding
involves physical context in which memory stored + retrieved
More cues mean better recall
Free recall: open ended question + supply answer from memory
Cued recall: given prompt/clue to correct answer
Recognition: pick out answer from list of possible options
Free recall harder than cued recall, harder than recognition
Free recall provides no explicit cues
Cued recall provides at least some cues
Recognition, entire item is provided
Forgetting
Directed forgetting: info is forgotten on-demand
Intentional forgetting extend to autobiographical events: Memory suppression in which individuals forget highly dramatic and unpleasant events
Interference
memories overlap in content, strength of either/both memories may be reduced
Proactive interference: old info can disrupt new learning
Retroactive interference: recently acquired info interferes with old memory
Memory misattribution
Remember info but mistakenly associated with incorrect source
Source amnesia: we remember info, but cannot remember source at all
Cryptonisia: mistakenly thinks thoughts are novel when actually remembering info learned somewhere else
False memory
Memories of events that never actually happened
Tend to occur when ppl prompted to imagine missing details
•Later mistakenly remember details as truth: form of memory misattribution
more that ppl imagine event, more they’re likely to subsequently believe it really happened
•Eyewitness memory is prone to error
Memory consolidation and reconsolidation
Consolidation Period: Time window during which new memories vulnerable + easily lost
Memory consolidation and reconsolidation
ECT: Used for people with severe depression
•Old memories can be disrupted if recall just before administration of drugs that block formation/maintenance of synaptic connections
Each time an old memory is recalled to reactivated, it may become vulnerable again + need to be reconsolidated
cerebral cortex and semantic memory
Sensory cortex: cortical areas that specialize in a kind of sensory info
Association cortex: other cortical areas, involved in associating info within + across modalities
Cerebral cortex primary storage site for many kinds of semantic info
Agnosia: relatively selective disruption of ability to process particular kind of semantic info when there’s cortical damage
cerebral cortex and semantic memory
Auditory agnosia for speech: can hear sounds an echo them but unable to understand meaning
Associative visual agnosia: difficulty recognizing + naming objects even though they can see them
cerebral cortex and semantic memory
- Some neurons respond to pictures of particular categories of objects
- Some neurons respond to many pictures, others respond to none
- Individual neurons in various areas of the cortex + frontal and Temporal lobe show surprising selectivity
- We have networks of neurons that respond primarily to info representing simple, familiar categories
hippocampus and cortex interact during memory consolidation
•Ribot gradient: retrograde memory loss for events that occurred shortly before injury, then for events that occurred in the distant past
•Bilateral medial Temporal lobe damage show some retrograde + anterograde amnesia
•Standard consolidation theory: hippocampus + related medial temporal lobe structures required for the initial storage + retrieval of an episodic memory but contribution diminishes overtime until cortex is capable of retrieving memory without hippocampal help
Initially all components linked together via hippocampus into unified episodic memory
hippocampus and cortex interact during memory consolidation
Over time components form direct connections + no longer need hippocampal mediation
Multiple memory trace theory: episodic memories encoded by an ensemble of hippocampal + cortical networks and cortical networks never become fully independent of hippocampal networks
Individuals might be able to rehearse a piece of autobiographical info so many times that it becomes a semantic memory
hippocampus and cortex interact during memory consolidation
Hippocampus gradually decrease as age of semantic memory increases + remains low during recall of memories from 13 to 30 years ago
Other brain areas including cortical areas in frontal lobe, Temporal lobe, parietal lobe showed higher activity for old than for new memories
frontal cortex and memory storage and retrieval
Frontal cortex may help determine what info we store + don’t store
Left frontal lobe more active during incidental encoding of subsequently remembered info
•Other areas of PFC may suppress hippocampal activity, inhibiting storage + retrieval of unwanted memories
•Several areas + PFC more active during forget trials than during the remember trials
frontal cortex and memory storage and retrieval
contextual info to event memory, allowing us to form episodic memories that encode what happened + where + when
Subcortical structures involved and episodic and semantic memory
Basal forebrain – collection of structures at base of forebrain
Nucleus basalis + medial septal nuclei produce neuromodulator acetylcholine + distributed throughout brain
Diencephalon: area near core of the brain, just about brainstem that includes Thalamus, hypothalamus + mammillary bodies
Subcortical structures involved and episodic and semantic memory
Thalamus release info from sensory receptors to appropriate areas of sensory cortex
Hypothalamus plays important role in regulating involuntary functions (heartbeat, appetite, temperature control, wake sleep cycle)
Fornix: parts of basal forebrain + diencephalon connect with hippocampus via arch like fiber bundle
basal forebrain may help determine what the hippocampus stores
medial septum + basal forebrain, sends acetylcholine + GABA to hippocampus where they affect activity + synaptic plasticity of hippocampal neurons
projections determine whether + when hippocampus will process + store info
Basal forebrain damage: hippocampus can’t work effectively without neuromodulation from basal forebrain telling it when to store new info
Confabulation: individuals with basal forebrain damage will respond with highly detailed but false memories
Diencephalon may help guide consolidation
Korsakoff’s disease: condition caused by deficiency of thiamine that sometimes accompanies chronic alcohol abuse
damage to areas of diencephalon
Develop anterograde amnesia
Diencephalic structures help mediate interaction betw frontal cortex + hippocampus during memory storage + consolidation, so damage disrupts this interaction
•Many structures – hippocampus, cortex, Diencephalon + basal forebrain – must all be working well + together for episodic + semantic memory to function properly
