[Δ-, θ-Modulation of the Ventral Tegmental Area Fast-Gamma Activity in the Course of Performance of Conditioned...

The prestimulus expectation period of conditioned avoidance reflex features synchronized Δ-rhythm (1-4 Hz) in the medial prefrontal cortex and the ventral tegmental area (VTA), and synchronized θ-rhythm (6-8 Hz) in the above-mentioned structures and the hippocampus. According to "Granger causality" Δ- and θ-rhythms flow (are predictors) in the direction from the prefrontal cortex and the hippocampus to the VTA. Performance of conditioned avoidance reflex was marked by Δ-rhythm elimination simultaneously with generation of high-frequency (8-11 Hz) synchronized θ-rhythm. Δ-rhythm was shifted from the pre- to poststimulus period and prefrontal cortex--VTA θ-synchrony was eliminated in the cases of mistaken reaction withdrawal, Pavlovian fear conditioning scheme, conditioned signal presentation in the safe chamber part. The phase of Δ-, θ-rhythm modulates the amplitude of VTA fast (70-160 Hz) γ-activity envelope, VTA/cortex and VTA/hippocampus γ-phase synchronization and phase lag indexes, and frequency of simultaneously recorded VTA neuronal activity.