Eeg Evidence of 1st Order Phase Transitions by Neural Populations in Gamma Activity of Sensory Neocortices of Trained Rabbits and Cats

Multichannel EEG recordings from trained animals with high-density epipial arrays of electrodes fixed on cortical sensory areas reveal spatiotemporal patterns. These patterns have the form of temporal modulations of the phase (PM) and amplitude (AM) of spatially coherent carrier waves with frequencies in the gamma range. The patterns form and dissolve at rates in and below the theta range. AM patterns serve to classify EEG segments with conditioned stimuli (CSs). Phase patterns (radially symmetric) show episodic synchronization. Fine temporal resolution of the analytic phase using the Hilbert transform indicates that pattern formations are by 1st order phase transitions