Fig 2. Adaptation tunes cortical dynamics from large-scale transient response to scale-free steady-state.

(A) Motion-enhanced movies were projected onto the retina while recording local field potential (LFP) with a microelectrode array in visual cortex of the turtle ex vivo eye-attached whole-brain preparation. (B) Shown are LFP traces from a subset of 12 electrodes. Intense population activity occurs at the onset of the movie; adaptation leads to more moderate steady-state activity. To characterize these changes in population activity, we analyze ‘avalanches’ which are defined as spatiotemporal clusters of LFP peaks beyond ±3 SD (black ticks). Avalanche size was defined as the number of LFP peaks comprising the cluster. (C) LFP peak rate time series, averaged over 80 movie repetitions. (D) Each point represents the size and time (middle of duration) of one avalanche. Avalanches from 80 trials are overlaid. Avalanches were typically very large during the transient response, but adaptation resulted in smaller and more diverse sizes. (E) Typical distributions of avalanche sizes during the transient (blue, 0–1 s after movie onset) and the baseline period (green, 2–5 s after movie onset). During the transient, the distribution exhibited a ‘bump’ at large size indicating a high likelihood of very large avalanches. During baseline, avalanche size distributions were well-described by a power-law function, in line with recent findings that adaptation tunes cortical network dynamics to criticality. Green box delineates the expected range (5–95 percentile) of probabilities for a finite sample drawn from a perfect power law. (F) To quantitatively characterize population dynamics during different time periods we computed δ, which measures deviation from the baseline distribution. Calculation of δ is based on differences between cumulative distributions like the examples shown. (G) Shown is a summary of 14 experiments. Without exception, the transient exhibited many more large avalanches than the baseline (δ>0) while the steady state period (4–5 s after movie onset) exhibited small deviations, both positive and negative, from baseline.