Fig. 8: Phase-locking of spikes to theta oscillations.

a Top, theta oscillations (red line) from three representative electrode sites and the single-unit spikes that occurred at each of those electrodes (black dots). Bottom, zoomed in view from the gray box on the top. b Left, circular distribution of theta phase angles occurring during single-unit spike events measured from the electrodes in a. Direction of the mean spike angle (µ) relative to the theta phase and magnitude (mean resultant length) are shown in the polar plots. The Rayleigh test for non-uniformity was used to determine if spikes were distributed non-uniformly over the theta cycle (0°, 360°). Right, distributions of theta-spike angles shown relative to the theta cycle are visualized as histogram plots. c Top, a cluster of phase-locked units to theta oscillations are shown within the coherent pocket highlighted by the box in Fig. 7d. The color indicates the mean phase-locked angle to theta (µ) that satisfy the Rayleigh test for non-uniformity (p < 0.05). A subset of the total electrode sites with no preferred theta phase (n = 102, p > 0.05) are shown by gray dots. Bottom, histogram of the mean phased-locked angle to theta for all electrode sites across the array that satisfy the Rayleigh criteria (n = 29, p < 0.05) which account for 22% of the 131 total active units detected. We observe an average of 28% ± 14% of single units exhibiting phase-locking to theta oscillations based on the Rayleigh criteria defined above (n = 4 organoids at 8 months).