Figure 1.

Three Different Dynamical Regimes that Could Explain Variability Modulation by Stimuli

(A–C) Two schematic neural trajectories (red and green) corresponding to two separate trials are plotted for each dynamical regime, before (top) and after (bottom) stimulus onset. Spontaneous activity is redrawn in gray beneath evoked activity to allow comparison of variability. Dotted ellipses outline activity covariances around the fixed point(s) of the dynamics (if any exist).

(A) Multi-attractor dynamics: spontaneous activity wanders stochastically between a set of attractor states (three shown), resulting in large trial-by-trial variability (top). Stimulus onset constrains fluctuations to the vicinity of a single attractor, reducing variability across both time and trials (bottom).

(B) Chaos suppression: chaos yields large across-trial variability in spontaneous dynamics (top), which is suppressed by the stimulus, leading to a reduction of variability across trials but not necessarily across time (bottom).

(C) Stochastic SSN: both spontaneous and evoked dynamics are stable with a single fixed point, but the stimulus can shrink the effective size of the basin of attraction of the fixed point (as well as shifting its location), resulting in a reduction of both across-time and across-trial variability.