Hippocampal EEG and information processing: A special role for theta rhythm
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This review analyzes the significance of the principal EEG patterns in the hippocampal EEG: low voltage, fast activity (LVFA), rhythmic, slow activity (RSA), and high voltage, slow (irregular) activity (HVSA), as they may relate to the underlying information processing reactions. Emphasis is given to the significance of RSA and its shifts in frequency. The cause of RSA is presumed to result from the compounding of both postsynaptic potentials and staccato firing of impulses in fiber tracts which is made possible by the special microanatomy of the hippocampus. The hippocampus is proposed to hace three distinct operational modes, as reflected in LVFA, RSA, and HVSA. Modes are assumed to be switch-selected by the input pattern of firing, with one kind of brain reticular drive creating a septal burst pattern the engages the RSA mode, and another kind of reticular drive disrupting the burst pattern and engaging the LVFA mode; lack of reticular drive causes a passive lapse into the HVSA mode. Frequency shifts during the RSA mode could result from a change in number and/or phase relation of contributing impulses and postsynaptic potentials, all of which are readily modified by changes in septal, entorhinal, or reticular inputs; the dentate mossy fiber pool is considered as a critical gate control system for frequency regulation. The consequences of RSA are presumed to be: (1) possible electrotonic action; (2) unified operation as a system of certain circuits within hippocampal "chips"; (3) stereotypical processing of information and (4) RSA involvement in input detection and transformation, analysis of raw and manipulated input data, and delivery of output. Specific examples are given for such postulated output functions as probability biasing, gating (Boolean) and scanning. Finally, such reactions are evaluated in the context of hippocampal relationships with other brain areas and in terms of phylogenetic significance. © 1976.
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