Hippocampus & the Striatum

Scoville Operation: Patient HM

• bilateral medial temporal lobe resection = removal of the hippocampus and nearby tissue structures including (medial temporal lobe)

• reduced seizures, but led to memory problems

HM brain functioning (9)

• “emotional placidity” (no complaints)

• no effect on intellect & language

• STM for about 5-10 mins after experience

• massive anterograde amnesia

• moderate retrograde amnesia

• little learning of declarative memories

• impaired episodic memory

• intact procedural

• poor new explicit & almost normal implicit memory

Explicit memory

recall of information which one knows is in memory

Implicit memory

influence of recent experience on behavior even though one doesn't recognize memory is being used

Medial Temporal Lobe

entorhinal, perirhinal, and parahippocampal cortices as well as the amygdala

MTL: Declarative Explicit Memory

damage leads to impairment in storing any new memories for facts (declarative memories) and events (episodic memories)

"What is "The Knowledge" for London, England taxi drivers? (spatial memory)

• demanding test that assesses a candidate's in-depth knowledge of London's streets, landmarks, and routes

• takes 3-4 years

• 7 stages of exam

Eleanor Maguire

• studies show high levels of activation via PET scans for spatial related questions (what is shortest distance between..)

• drivers have larger posterior hippocampi than normal

Birds "navigational grid & place cell" system

• discovered by John O’Keefe

• birds finding hidden seeds during winter rather than storing →larger hippocampi relative to those who have poor spatial memory & store food

“Place Cells” (John O’Keefe)

• when rats move to different places, cells in hippo fire → creates mental map

• cells have memory function → animals able to navigate same place in future

“Grid Cells”

• Britt & Moser

• entorhinal cortex → fire as rat moves & arranged in hexagonal patterns

• provide a knowledge of place & the direction of the animal's head → allowing to calculate distance

"Internal Continuous GPS System"?

the entorhinal and hippocampal cells of a rat create an “updated GPS” understanding of what surrounds the animal & updated positioning signal→ animal knows location and destination

"striatum"

involved in modulating the movement of our muscles and learning

Gradual implicit or habit learning

depend upon a diverse set of nuclei in the basal ganglia: striatum (putamen & caudate nuc), globus pallidus, substantia nigra, & subthalamic nuclei → use DA as neurotransmitter (movement)

Striatum & "reinforcement level learning"

• Gradual learning (multiple trials)

• Learning habits and skills

• requires prompt feedback (= reward or punishment is clear)

• is implicit (put into actions)

• If damaged, the ability to learn new skills or habits is impaired and past skills/habits often impaired as well