Neuroscience
-
Review of the normally occurring neuronal patterns of the hippocampus suggests that the two principal cell types of the hippocampus, the pyramidal neurons and granule cells, are maximally active during different behaviors. Granule cells reach their highest discharge rates during theta-concurrent exploratory activities, while population synchrony of pyramidal cells is maximum during immobility, consummatory behaviors, and slow wave sleep associated with field sharp waves. Sharp waves reflect the summed postsynaptic depolarization of large numbers of pyramidal cells in the CA1 and subiculum as a consequence of synchronous discharge of bursting CA3 pyramidal neurons. ⋯ It is assumed that recurrent excitation during the population burst is strongest on those cells which initiated the population event. It is suggested that the strong excitatory drive brought about by the sharp wave-concurrent population bursts during consummatory behaviors, immobility, and slow wave sleep may be sufficient for the induction of long-term synaptic modification in the initiator neurons of the CA3 region and in their targets in CA1. In this two-stage model both exploratory (theta) and sharp wave states of the hippocampus are essential and any interference that might modify the structure of the population bursts (e.g. epileptic spikes) is detrimental to memory trace formation.