What is learning?
a change in behaviour as a result of experience
What is memory?
the changed behaviour resulting from learning
Where do the IT and prefrontal cortexes signal?
the medial temporal cortex (not part of the neocortex)
What surgery did HM undergo?
a bilateral medial temporal lobectomy to surgically resect the anterior two thirds of his hippocampi, parahippocampal cortices, entorhinal cortices, piriform cortices, and amygdalae in an attempt to cure his epilepsy
What were HM’s symptoms after surgery?
- unable to recognise hospital staff
- recalled nothing of the day-to-day events of his hospital life
- partial retrograde amnesia
- unable to form new memories but early memories were intact
What is partial retrograde amnesia?
a condition where a person loses some, but not all, memories from before the onset of amnesia, typically affecting more recent memories while sparing older ones
What is the first major lesson from HM?
- some MTL structures are needed for forming and storing new long-term declarative memories
- some remote (oldest) memories are independent of the MTL structures needed for forming new declarative memories and for recalling more recent declarative memories
How are declarative memories tested?
by asking simple questions e.g. what did you have for breakfast?
How does the MTL relate to memory?
it is required to form new memories but as the memory gets older, it is no longer required to recall
What is cellular consolidation?
a quick process at the synaptic level that stabilises memory traces
What is systems consolidation?
a slower process that reorganises and transfers memories from the hippocampus to the cortex for long-term storage
What happens in the initial stage of memory consolidation?
- strong connections exist between the hippocampus and various cortical modules
- the hippocampus plays a central role in linking different cortical modules, acting as a hub for integrating and retrieving memories
What happens in the intermediate stage of memory consolidation?
the connections between the hippocampus and the cortex begin to weaken, while connections within the cortical modules strengthen
What happens in the final stage of memory consolidation?
- eventually, the memory becomes primarily stored in the cortex, with strong interconnections between the cortical modules and significantly reduced dependence on the hippocampus
- the cortical modules are now sufficiently interconnected to support memory retrieval independently of the hippocampus
What is the second major lesson from HM?
- procedural learning is independent of the MTL structures needed for forming new declarative memories
- different types of memory involve different parts of the brain
What structures are responsible for declarative memory?
hippocampus and parahippocampal region
What structures are responsible for procedural memory?
brainstem and spinal motor outputs, striatum and cerebellum
What structures are responsible for emotional memory?
hypothalamus, autonomic and hormonal outputs and amygdala
What are possible reasons for HM still being able to acquire some declarative memories?
- spared MTL structures e.g. posterior parrahippocampal cortex
- sufficient repetition may overcome loss of some MTL structures
What is one possibility of learning being due to changes in the brain?
learning is due to a change in the strength of connections between neurons
What is the Hebbian idea?
pre and post synaptic neurons must be active at the same time to have LTP
What is LTD?
a persistent decrease in synaptic strength that can be NMDA receptor-dependent and independent
What is LTP?
a persistent strengthening of synapses based on recent patterns of activity
What synapses on CA1 neurons?
glutamate
