ABSTRACT
This chapter describes the state-dependent micro-electroencephalogram (EEG) events observed and their associated fast-frequency oscillations. It suggests that understanding the biophysical means by which distributed neurons in the hippocampal formation accomplish memory formation necessitates understanding state-dependent, neuronal dynamics. Whenever the rat moves, or attends to sensory stimuli, or is in rapid-eye-movement (REM) sleep, theta waves dominate the hippocampal micro-EEG. In the absensce of certain subcortical modulatory inputs that are engaged during exploratory activity and REM sleep in the rat, hippocampal and entorhinal circuits engage in aperiodic population bursts: hippocampal sharp waves, entorhinal sharp waves, and dentate spikes. The non-linear interplay between intrinsic membrane currents, network connectivity, associational synaptic input, and the actions of subcortical modulatory inputs allows a higher order dimension to the behavioral state-dependent symphonies played by hippocampal circuits. The biophysical means by which distributed neurons within these circuits interact and accomplish memory formation is embedded within these state-dependent symphonies.
