Figure 1.

The methodological approaches for the phase and time analysis of field potential and intracellular signals. A, Drawing represents a position of two electrodes used for EEG recordings. In all experiments, the EEG was recorded from the contralateral side compared with intracellular recordings. The EEG signal was filtered (bandpass 0.2–4 Hz), and then a Hilbert transform was performed. To extract EPSPs, we differentiated the intracellular potential over time and then we set up the threshold. Vertical red lines indicate identified EPSPs. IPSPs (three large-amplitude negative peaks are evidently seen here) were detected manually. B, Top, Averaged EEG. The zero time corresponds to the instantaneous phase −0.5. Bottom, Time histograms of EPSPs and IPSPs normalized by mean. C, Top, EPSP phase histogram for the same neuron before normalization by time. Because time spent in each phase is not identical, an artificial correlation between phase and EPSP occurrence is seen. Bottom, A time against phase histogram, which shows the average time duration of each phase bin (%). Because the amount of counts within each phase bin is proportional to its time duration, we divided the EPSP phase histogram by the time against phase histogram (i.e., we normalized the phase by time, bottom histogram). As expected, the EPSPs from ascending pathways were not phase-locked to the EEG (p > 0.05, Moore–Rayleigh test). D, Averaged EEG wave and intracellular potential plotted against phase using linear interpolation. EEG normalized by maximum values. Note averaged IPSPs on the intracellular wave.