9/21 Memory - Glendinning Flashcards
memory
process by which knowledge/experiences are encoded, stored, retrieved
allows us to…
- understand, predict our world
- recognize novelty
- learn from experience
- remember people
- navigate world through spatial relationships
- have cognitive framework for future learning
- know who we are
classification of memory
categories of memory
based on:
- nature of stored info
- time course of storage
categories of memory
1. declarative memory: medial temporal lobe, diencephalon
- can be brought to consciousness
- expressed by language (tel number, songs, past event)
- include:
- facts: semantic (stuff you “know”)
- events: episodic (stuff you “remember”)
2. nondeclarative memory aka procedural memory
- largely unconscious
- subcortically formed memories (ex. motor skills)
- include:
- procedural memory: skills/habits (striatum)
- classical conditioning
- skeletal musculature (cerebellum)
- emotional responses (amygdala)
short term declarative memory
classified based on timecourse into:
1. immediate memory
- ability to register info
- mental status exam: “repeat these three words immediately”
- brain areas: require attn (brainstem and cortical areas)
2. working memory/short term memory
- holding info long enough to use for a mental operation
- mental status exam: “digit span test” and “digit span backwards”
- brain areas: requires attn (brainstem and dorsolateral prefrontal cortex)
cortical neurons show changes that can create short-term memories
expt: cortical neurons activated repeatedly → short-term increases in firing rate that persis in case of stronger inputs
long after-depolarizations of cortical neurons → increased firing rates
- after-depol might be related to activation of voltage-gated Ca channels that are activated and then lead to opening of more cation channels → incr depol!
recent and long term memory
classified based on timecourse into:
1. recent memory
- remembering what you did minutes-days ago
- mental status exam: “name the objects you saw 5 mins ago”, “what did you eat for breakfast yest”
- brain areas: medial temporal cortex, diencephalon
2. long term memory
- basic historical facts about lives
- mental status exam: “who is the president” “what year were you born” “what town do you live in
- brain areas: medial temporal and specific cortical regions
these involve the limbic system!
Papez circuit
for learning and memory formation
HM and lessons learned
HM fell off his bike, had bad seizures
- got bilateral medial temporal lobe removal
- HM was left with
- inability to produce new memories (anterograde amnesia) from point of surgery onwards
- inability to retrieve established memories (retrograde amnesia) befor approx 15 years prior to surgery
lets us know that hippocampus plays a role in memory formation AND memory storage to a point
- far enough back, memories are prob stored directly in cortex
HM was tasked with mirror drawing experiment
- number of errors decreased over time spent on task, despite the fact that he could not remember doing the process before
- lets us know that there are multiple memory systems!! motor learning too!
role of hippocampus in memory formation
hippocampus receives simultaneous inputs from the entire cortex
- uniquely able to relate “what”, “where”, “when” something happens from different cortical areas
when cued (after the event has occurred), hippocampus can trigger these associations between otherwise disparate cortical areas
eventually, dont need hippocampus bc the memory tract in cortex is so strong
- evidence: people with hippocampal loss dont have loss of the v long term memories!
parts of hippocampus
lots of neuroplasticity in cells of hippocampal formation
3 layered cortex (in region of floor of lateral ventricle)
1. DENTATE:
- molecular
- granule cell
- polymorphic
2. SUBILICULUM and HIPPOCAMPUS (CA1-CA2-CA3)
- molecular
- pyramidal cell
- polymorphic
hippocampal connections and long term potentiation
in rat brain…
entorhinal cortex (similar to human parahippocampal gyrus) sends projections to
→ granule cells in dentate gyrus, which sends mossy fibers to
→ CA3 pyramidal cells, which send Shaffer collateral to
→ CA1 pyramidal cells (major output of hippocampal formation)
- CA1 hippocampal neurons display LTP: after receiving repeated input, they respond more strongly to those inputs (larger EPSPs)
- aka “Hebbian synapse”
what events allow for long term potentiation?
1. insertion of new receptors
- Glu binds to AMPA and NMDA receptors → Ca channels open
- Ca acts as second messenger : signals nucleus to produce more AMPA receptors
- result: cell becomes more responsive to excitation
- evidence: no LTP or learning in presence of NMDA antagonists
2. changes in dendritic spines
- dendritic spine formation observed within an hour of LTP induction, with memory formation
3. adult neurogenesis in dentate gyrus
- evidence: blocking neurogenesis can block spatial learning in animal models
- neurogen increased with exercise!
hippocampal roles in…
experiments and conclusions
spatial orientation: swimming rats with hidden platforms
- rats with hippo lesions don’t demonstrate spatial orientation improvement/learning
recall: single neuron responses tracked to visual stimuli - same neuron fired on watching “Simpsons” clip and just before recallin “Simpsons” clip
consolidation, retrieval, reconsolidation cycle
experience
- stored in short term memory until…
- consolidation of learning (hippocampus/amygdala) into long term memory
triggering of memory
- extinction (prefrontal cortex poss involved)
-
retrieval, which involves reconsolidation if occuring during the period of lability
- concl: memory retrieval is “constructive”, and can be influenced by thoughts/mood/suggestion!!!
forgetting
potentially adaptive
- removes confusion in our thought processes
- voluntary forgetting: prefrontal cortex inhibition of hippocampal retrieval system
memory loss syndromes
Alzheimer’s disease
forgetfulness, anterograde/retrograde amnesia, cognitive impairment, disorientation, abnormal behavior
cause:
- degeneration of hippocampal and parahippocampal neurons
- loss of cholinergic cells in basal forebrain nuclei (project to cerebral cortex)
