Hippocampus Flashcards
where was patient HM’s lesion that caused his epilepsy?
behind frontal lobe
what type of memory was affected in HM?
declarative / episodic memories
what is declarative/explicit memory?
events (episodic memory) and facts (semantic memory)
what is nondeclarative/implicit memory?
procedural memory, perceptual representation, classical conditioning, nonassociative learning
what does CA stand for?
Cornu amonis
what contains the hippocampal formation?
CA1-3, dentate gyrus, entorhinal cortex, subiculum, pre and Para-subiculum
what is the human hippocampus volume compared to rat and monkey?
human hippo volume is 100x bigger than a rat’s and 10x bigger than a monkey’s
what type of cells are in the dentate gyrus and CA1/3 and how many?
- DG = 1.2 million GRANULE cells, 4000 basket cells, 32 000 hilar interneurons
- CA3/1 = 330 000 to 420 000 PYRAMIDAL cells, many interneurons too
what layers of the entorhinal cortex project where?
- layer II = DG and CA3
- layer III = CA1 and subiculum
what layer of EC receives input from what region of the hippo?
EC layer 5 receives from CA1 and subiculum
what synapse is one of the largest and most powerful in the brain?
the mossy fiber synapse!
what type of connections are between DG and CA3 and CA1?
DG -> mossy fibers -> CA3 -> schaffer collaterals -> CA1
what are the 3 inputs going to CA3? how many of each?
- 50-80 mossy fibers from DG
- 3 500 perforant pathway from EC layer 2
- 12 000 recurrent collaterals from CA3
the recurrent collaterals in CA3 are separated between what?
they either go to basilar dendrites (8000) or to apical dendrites (4000)
where does CA1 get input from?
- schaffer collaterals from CA3
- from EC layer 3
where does the medial vs lateral EC projections separate and where do they each go to?
medial EC layer 3 go to proximal CA1, lateral EC layer 3 go to distal CA1
what is the hillus reciprocally connected to?
to the DG
what does inactivation of the medial septum do in rodents? how was it tested?
impairs memory! rats can’t remember where the platform is in the water maze anymore
what type of memory is encoded in the hippocampus?
episodic memory (type of declarative memory)
what kind of hippo lesions disrupt memory performance in the water maze?
mostly dorsal lesions
how did they test for how long it takes for memory to move from the hippo to the cortex?
- they shock a rat at the same time as a tone: rat associates tone with shock
- they lesion the hippo after 1, 7, 14 or 28 days
- then test if the rat freezes when it hears the tone to see if it remembers the tone-shock association
what were the results of the tone-shock pairing and hippo lesions experiment? what can we conclude?
when lesioning the hippo after 28 days, the rat remembers the tone-shock pairing (freezes when hearing the tone), meaning the memory moved to the cortex
what do you call memory that moved from hippo to the cortex?
semantic memory
what is high pass filtering used for in extracellular recordings?
filter out the frequencies below 800Hz (local field potential) to look at higher frequencies only (spikes)