State-Dependent Changes in Network Activity of the Hippocampal Formation
17 Sep 2019-pp 349-362
TL;DR: In this paper, the authors describe the state-dependent micro-electroencephalogram (EEG) events observed and their associated fast-frequency oscillations and suggest that understanding the biophysical means by which distributed neurons in the hippocampal formation accomplish memory formation necessitates understanding statedependent, neuronal dynamics.
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.
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3,359 citations
TL;DR: The phase was highly correlated with spatial location and less well correlated with temporal aspects of behavior, such as the time after place field entry, and the characteristics of the phase shift constrain the models that define the construction of place fields.
Abstract: Many complex spike cells in the hippocampus of the freely moving rat have as their primary correlate the animal's location in an environment (place cells). In contrast, the hippocampal electroencephalograph theta pattern of rhythmical waves (7-12 Hz) is better correlated with a class of movements that change the rat's location in an environment. During movement through the place field, the complex spike cells often fire in a bursting pattern with an interburst frequency in the same range as the concurrent electroencephalograph theta. The present study examined the phase of the theta wave at which the place cells fired. It was found that firing consistently began at a particular phase as the rat entered the field but then shifted in a systematic way during traversal of the field, moving progressively forward on each theta cycle. This precession of the phase ranged from 100 degrees to 355 degrees in different cells. The effect appeared to be due to the fact that individual cells had a higher interburst rate than the theta frequency. The phase was highly correlated with spatial location and less well correlated with temporal aspects of behavior, such as the time after place field entry. These results have implications for several aspects of hippocampal function. First, by using the phase relationship as well as the firing rate, place cells can improve the accuracy of place coding. Second, the characteristics of the phase shift constrain the models that define the construction of place fields. Third, the results restrict the temporal and spatial circumstances under which synapses in the hippocampus could be modified.
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