hippocampus Flashcards
HM and episodic memory
surgery for epilepsy on both sides of brain (hippocampus, amygdala and surrounding cortex)
severe anterograde amnesia
short term/working memory intact
intact language
able to acquire new motor skills
impaired spatial memory
maguire 2000
spatial memory
taxi drivers and their hippocampi- longer they are a texi driver the greter the grey matter density of the hippocampus (posterior not anterior)
lesions to hippocampus disrupt spatial memory
morris water maze
a mouse in water will find where a platform is
what are place cells?
cells in the hippocampus that tell us about where we are in the environment
they fire when an individual is in a specific location in its environment
cortico-hippocampal information flow
primary sensory cortices feed info to the association cortices to the parahippocampal cortex, entorhinal cortex and then hippocampal formation
anatomical connections between the hippocamous and cortex
parahippocampal cortex –site of convergence for cortical input
in the hippocampus divergent and convergent connections are involved in formation of associations
outgoing information from the hippocampus is sent back to parahippocampal cortex
hippocampal anatomy
dentate gyrus
CA3 which runs into CA1
subicular
excitatory hippocampal pathway
- entorhinal cortex sends input to dentate via perforant path
- dentate contains granule cells
- dentate project to CA3 pyramidal cells through mossy fibres
- CA3 project to CA1 pyramidal through schaffer collaterals
- CA1 sends output to the subiculum and back to the entorhinal cortex, closing the loop woth the neocortex
connectivity in the hippocampus: a trisynaptic view
layer II and II of the neocortex send input into entrohinal cortex (2,3,5,6)
entorhinal layers II and III form perforant pathway to dentate gyrus
dentate gyrus to CA2 to CA1/ CA3 via mossy fibre pathway to CA1 schaffer collateral pathway to subiculum and back to V/VI of the entorhinal cortex
connectivity in the hippocampus: parallel processing
projections from entorhinal cortex dont follow trisynaptic route and dont go through dentate gyrus (e.g entorhinal cortex layer III to CA1, dentate to CA2 to CA1, CA2 to CA3 independently project to CA1)
anatomy of CA (1,2,3,4) pyramidal neurons
CA regions consist of a number of strata:
- stratum oriens
– s. pyramidale
– s. lucidum (CA3 only)
– s. radiatum
– s. lacunosum-moleculare
anatomy of CA3 pyramidal neurons
pyramidal shaped soma
apical and basal dendritic trees
afferents from entorhinal cortex, dentate gyrus and from other CA3 cells (via associational
commisural fibres)
efferents to CA1, CA2 (via schaffer collaterals), CA3, lateral
septal nucleus (via fimbria)
mossy fibres come in via the s.lucidium
head direction and boundary cells
head direction=subiculum, thalamus and entrohinal cortex
head direction fire based on the direction youre pointing in
boundary cells= extend of the envornment and where it ends
what are grid cells?
neurons in layer II and II in medial entorhinal cortex that fire in hexagonal, grid like pattern
the influence of grid cells on place cells…
- grid cells provide spatial information that helps place cells
- as animal moves through space the grid cells activate in a hexaginal pattern based on its position
- the hippocampus can use this spatial map from grid cells to encode the specific location (place field)
what are boundary cells?
medial entorhinal cortex neurons that activate when an animal is near edges or walls
the influence of boundary vector cells on place cells…
BVCs encode the distance and direction to boundaries and this info can be intergrated into the hippocampus to help place cells form location based firing patterns
