Origin, structure, and role of background EEG activity. Part 3. Neural frame classification

OBJECTIVE To show that cortical responses to conditioned stimuli (CS) include intermittently induced spatial patterns of amplitude modulation (AM) of beta-gamma oscillation called frames. METHODS EEGs were recorded from 8x8 high-density arrays fixed on primary sensory cortices of rabbits trained to discriminate CS with reinforcement (CS+) from those without (CS-). EEG frames were located with a pragmatic information index, H(e). The spatial patterns of the first 3 frames on each of 37-40 trials were measured by the square of 64 analytic amplitudes from the Hilbert transform to give points in 64-space. The questions were asked: Did the frames from CS+ trials and CS- trials differ within each sequential group? Did the 3 frames differ from each other (form 3 clusters of points)? RESULTS EEG frames that were identified by high H(e) had AM patterns that could be classified with respect to CS+ and CS- well above chance levels. Two stages of correct frame classification occurred on each trial: 40-130 ms after CS onset with a gamma carrier frequency, and 450-550 ms with a beta carrier frequency. Peak power in the beta frames was double that in gamma frames, and mean pattern surface area of beta frames was nearly 4-fold greater. CONCLUSIONS Under the impact of a CS on a sensory neocortex, the background EEG activity reorganized in sequential frames of coordinated activity, first local and modality-specific, thereafter global. SIGNIFICANCE The size, texture and duration of these AM patterns indicate that spatial patterns of human beta frames may be accessible with high-density scalp arrays for correlation with phenomenological reports by human subjects.