Wk 7: Colour spaces and pathology, memory and HM/clinical studies

7b: Memory

How To Navigate The Central nervous system

learning and memory

  • the brain handles diff kinds of memory in diff regions

    • classical conditioning

    • automatic association

    • amygdala and cerebellum

    • operant conditioning (rewards and punishments)

    • goal-directed learning

    • bassal ganglia and frontal cortex

  • encoding of memories: how experiences becom stored in the brain

    • Hebbian learning

    • cells that fire together, wire together

    • when two neurons activate together repeatedly, their connection strengthens

    • forms the basis of long term memory

Patient HM case

  • had parts of the brain removed to treat epilepsy

  • couldn’t form new long term memories

  • hippocampus critical for memory consolidation

learning: acquiring new info

memory: storing that info

important brain areas

limbic system

network of structures curving through each hemisphere

crucial for emotion and learning/memory (also motivation and olfaction - smell)

includes: 

  • hippocampus

  • amygdala

  • fornix 

7c: HM and other clinical studies

amnesia

types: 

  • retrograde - forgets the past

    • loss of memory prior to the event

    • loss of past memories

    • involves temporal lobes, hippocampus and surrounding cortex

    • disrupts retrieval pathways

  • anterograde - can’t make new memory

    • loss of memory after an event

    • inability to form new memories

    • long term memory fucked

    • short term memory may still be usable

    • involves hippocampus and medial temporal lobe (for memory consolidation (making something stronger))

    • prevents new info from being transferred into long term storage

memory

types based on duration:

  • short term STM

    • info that is currently held in the mind

    • stays for 30s unless repeated

    • has limited capacity

  • long term LTM

    • info that is stored

    • considered to have unlimited capacity

LTM

types: 

  • declarative - what

    • typically thought of as memory

    • facts and info

    • things that can be declared

  • nondeclarative/procedural - how

    • memory about perceptual or motor procedures

    • shown by performance

    • not by conscious recollection

    • e.g. riding a bike, playing a guitar

types of declarative

  • episodic

    • remembering autobiographical info

    • episodes of your life

  • semantic

    • generalised declarative memory

    • e.g. meaning of the word (do not need to know where and when the word was learnt)

example: chess

  • episodic: first time playing chess

  • semantic: rules of the game

types of non declarative

  • skill learning

    • learning a motor skill via repeated trials

  • priming/repetition priming

    • a change in the processing of a stimulus

    • e.g. shown the word stamp, then asked to complete this word: STA__

  • conditioning

    • learning simple associations between stimuli

required memory stages

a functional memory system requires

  1. encoding

  2. consolidation/strengthening

  3. storage

  4. retrieval

memory stages

  1. sensory info goes through encoding

  2. encoded info goes to short term

  3. short term goes through consolidation and strengthening and becomes long term

  4. retrieval of long term memory becomes working memory (shown through performance)

  1. sensory info goes through encoding

  2. encoded info goes to short term

  3. short term goes to working memory which is shown through performance

HM consequences

Henry Molaison had seizures in both temporal lobes

amygdala, most of the hippocampus and some surrounding context were removed in 1953

consequences: 

  • positive

    • seizures reduced

    • controllable with meds

  • negative

    • anterograde amnesia (can’t make LTM) for long term declarative memories

    • could retain a new fact only briefly

    • only had STM

HM knew something was wrong. no memories since surgery

other patients: had amygdala removed but not hippocampus. showed no amnesia

hence, hippocampus is vital for consolidation of declarative LTM

given that HM could retrieve old memories, the hippocampus can’t be the storage site

Patient NA

damaged the diencephalon (thalamus and hypothalamus) and other regions

anterograde amnesia (fucked LTM) primarily for verbal material

Korsakoff’s syndrome

  • typically caused by a lack of vitamin B1 (thiamine

  • shrunken/diseased mammillary bodies and some damage to the dorsomedial thalamus

  • anterograde amnesia

  • makes up stories they seem to accept as true to account for the gaps in their memory

consolidation and retrieval

hippocampus

  • important for consolidation of declarative memories

  • once stored, the hippocampus is not required for retrieval

—-

  • memories stored in other cortical regions

  • tend to be areas of the cortex where the info was first processed and held in STM

  • e.g. the visual cortex is crucial for visual object recognition memory

—-

medial temporal lobe

  • crucial for declarative memory

  • amygdala not important for declarative memories

  • cortex is important for storage

episodic vs semantic memories

stored and retrieved differently

patient KC

  • retrograde amnesia for episodic memories only

  • does not affect semantic declarative memories

  • also has anterograde amnesia for episodic only

  • again, does not affect semantic declarative memories

episodic:

  • relies heavily on the hippocampus for reconstructing time-bound experiences

semantic: 

  • stored diffusely across neocortex

  • especially lateral temporal and parietal area.