Theories of Function of Hippocampus

Hippocampus & Declarative Memory
1. patients with hippo damage acquire new skills, they have trouble learning new facts
2. Hippo is critical for declarative memory spec episodic memory
  1. Squire (1992)
3. Rat digs food out of 5 piles of sand each with different door.
  1. gets choice between 2 of doors and rewarded if goes toward the one it smelled first
    1. intact rats learn to respond correctly showing memory of smelled and when smelled it
      1. Rats with hippo damage do poorly on this task
4. Memory of specific event qualifies as episodic at least by broad definition
5. Delayed matching-to-sample task
  1. an animal sees an object and after delay gets a choice between two objects and must pick one that matched sample.
6. Delayed non matching-to-sample task
  1. procedure is same except that animal must choose object different from sample
7. Hippocampal damage strongly impair performance of delayed tasks
  1. Zola et al (2000)
Hippocampus & Spatial Memory
1. Electrical recordings indicate many neurones in rats hippo tunes to spatial locations
  1. responding best when an animal is in a particular place
    1. O'Keefe & Burgess (199^)
    2. Or looking in a particular direction
      1. Rolls (1996)
2. When performing spatial tasks, best route, fMRI results show enhanced activity in hippo
  1. Kumaran & Maguire (2005)
3. PET scans on London Taxi drivers on routes around London
  1. Answering activated their hippo much more than non spatial questions
  2. MRI scans revealed drivers have larger than average posterior hippo
    1. longer they had been taxi drivers, larger their posterior hippo
      1. Maguire et al (2000)
      2. Actual growth of adult human hippo in response to spatial learning experiences.
4. radial maze had several arms some or all have food at the end
  1. rat's best strategy is to explore each arm once and only once, remembering where it had already gone
    1. may have to learn that those with rough floor or pointing toward window never have food.
    2. Rats with damage to hippo gradually learn not to enter the never-correct arms but even after much training they often enter a correct arm twice.
    3. People with damage to hippo are slow to learn which arms never correct and free visit one arm before others
      1. Human data resemble those of rats
5. Morris water maze
  1. rat swims through murky water to find a rest platform that is just under the surface
Hippocampus & Contextual Memory
1. hippo is important for remembering details and context
2. recent memory, depends on hippo includes detail
  1. time causes memory to become less detailed, less dependent on hippo and more on cerebral cortex
3. Recalling old factorial memory may or may not activate hippo but episodic because include context details do activate hippo
  1. suited to dealing with observation that people with hippo damage have particular trouble with episodic

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