Figure 9. Trial-to-trial variability across a range of cortical states.

(A) Six examples of population responses to click stimuli, from a rat that exhibited stable dynamic state throughout the recording. Vertical green lines denote stimuli (time 0); LFP (black trace), activity of simultaneously recorded single neurons (rasters) and smoothed multi-unit activity (MUA; red trace) all show a pattern of population activity characteristic of the synchronized state. Right column shows an expanded view of the smoothed MUA in the response period for each trial; gray shaded areas denote “initial” (10-35ms; dark gray shading) and “persistent” (40-135ms; light gray shading) response periods. The stimulus may arrive during a downstate (trials 1, 2), at the beginning of an upstate (trials 3, 4), or well into an upstate (trials 5, 6). While preceding activity does not have a clear effect on peak activity levels in the initial response period, the timing of the stimulus relative to up/down transitions appears to modulate activity in the persistent response period. (B) Same conventions as in (a); all data are selected from a different recording session that showed variable dynamic state. In the synchronized state (trials 1,2), persistent responses are anticorrelated with activity levels in the 200-300ms preceding the stimulus. In intermediate states (trials 3,4), the stimulus induces a large initial response followed by a transient downstate. In the most desynchronized states (trials 5,6), responses exhibit a small but reliable initial response followed by a return to baseline, with no discernible persistent response. Adapted from Curto et al (2009).