Extended Data Fig. 2: Detection of spontaneous travelling waves.

a, The method for detecting spontaneous waves from the Generalized Phase. First, the detection algorithm found the most likely starting point for a putative wave as the point that maximizes the divergence of the phase gradient (step 1). b, With this source point found, the algorithm then quantified the spatiotemporal organization about this point from the circular-linear correlation of phase with distance across the whole array (step 2). With this approach, the algorithm can robustly detect arbitrarily shaped wavefronts in the array data. c, The average power spectrum for waves (N = 215) had significantly less power in low frequencies (<12 Hz) as compared to non-wave fluctuations (N = 524). Dotted bounds represent s.e.m. Asterisk: P < 1 × 10⁻⁵, two-tailed Wilcoxon rank-sum test. d, Detected waves in both monkeys predominantly travelled at speeds consistent with the conduction velocity of unmyelinated horizontal axons (0.1–0.6 m/s, red dashed lines; monkey W, 5571 waves, blue line; monkey T, 9285 waves, red line). e, There was no difference in the amplitude of fluctuations that were detected as waves (blue line; N = 696 waves) or rejected (non-wave, grey line; N = 565 non-wave fluctuations; example monkey T session).