place cell has place field in different part of environment Entorhinal cortex = area of medial temporal cortex; major source of neural signals to hippocampus o Grid cells – entorhinal neurons that have extensive array of evenly spaced place fields, producing pattern reminiscent of graph paper Distance b/w evenly spaced place fields = flexible (in experimental animals kept in smaller/oddly shaped environments, fields are closer together/sheared) Even spacing of grid cells could enable spatial computations in hippocampal place cells o Border cells – fire when subject is near borders of its immediate environment Nature of relationship b/w entorhinal grid cells & hippocampal place cells still debated o 2 lines of evidence suggested responses of hippocampal place cells depend on input from entorhinal grid cells 1) There is major pathway from entorhinal cortex to hippocampus 2) Entorhinal grid cells respond reflexively to location, whereas hippocampal place cells respond to place in combination w/ other features of environment o Discovery – properties of hippocampal place cells emerge in rat pups before stable firing of entorhinal grid Challenges idea that input from entorhinal grid cells essential for hippocampal place cell function Evidence that place cells can still function after entorhinal grid cells have been eliminated Comparative Studies of the Hippocampus & Spatial Memory Majority of evidence that hippocampus plays role in spatial memory comes from research on rats, but hippocampus performs similar function in other species o i.e. food-catching birds have remarkable spatial memories – must remember locations of hundreds of scattered food caches to survive Effects of hippocampal damage on performance of spatial memory tasks in humans/other primates – less consistent o Could be b/c spatial memory in humans/monkeys often tested while stationary & making judgements on computer screens, but in mice/rats/birds while navigating through test environments Hippocampus implicated in several forms of memory other than spatial
o Certain cells in hippocampus shown to code for temporal aspects of an experience (time cells) Jennifer Aniston Neurons: Concept Cells Major structures of medial temporal lobes – hippocampus, amygdala, medial temporal cortex o Medial temporal cortex composed of entorhinal, perirhinal, parahippocampal cortices Recording electrodes implanted in patients’ brains to record activity of certain neurons as they perform various tasks (many in structures of medial temporal lobes) o In one of the first neurons studied this way, neuron fired in response to images of actress Jennifer Aniston, but not to 80 other images o Other medial temporal lobe neurons discovered that responded to other individuals or objects known to patient Termed Jennifer Aniston neurons Concept cells – neurons that respond to ideas or concepts rather than particulars (also known as Jennifer Aniston neurons) o Highly selective; each neuron responded only to small # of test objects/individuals (often only one could be found)
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- Fall '19
- retrograde amnesia, temporal lobe