Answer to Question 1
Answer: The ability to navigate requires an intact hippocampus. H.M. has difficulties in spatial navigation. The firing rate of individual hippocampal cells was a function of the spatial location of the rat as it wandered around a maze. The external cues of the environment can control the firing rate of hippocampal cells, particularly of cells in the dorsal hippocampus (a key region for spatial navigation). The entorhinal cortex, which is an important input zone for the hippocampus, is also important for spatial navigation.
Answer to Question 2
Answer: LTP is an increased EPSP recorded from dentate cells to a single electrical pulse when that pulse was preceded by high-frequency electrical stimulation of axons that connect with the dentate gyrus cells. There is evidence that more glutamate may be released from the presynaptic terminal button (perhaps due to the influence of nitric oxide from the postsynaptic cell). On the postsynaptic side, LTP is accompanied by physical reorganization of the dendrite, which includes the insertion of AMPA receptors into the dendrite (more sensitivity to glutamate) and the formation of new dendritic spines, which would serve to increase the postsynaptic response to glutamate. Longer term potentiation involves changes in protein synthesis, in particular that of PKM-zeta.
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