Figure 1.

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 MUA (red trace) all show a pattern of population activity characteristic of the synchronized state. The right column shows an expanded view of the smoothed MUA in the response period for each trial; gray shaded areas denote “initial” (10–35 ms; dark gray shading) and “persistent” (40–135 ms; light gray shading) response periods. The stimulus may arrive during a downstate (trials 1 and 2), at the beginning of an upstate (trials 3 and 4), or well into an upstate (trials 5 and 6). Whereas 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 (synch) state (trials 1 and 2), persistent responses are anticorrelated with activity levels in the 200–300 ms preceding the stimulus. In intermediate states (trials 3 and 4), the stimulus induces a large initial response followed by a transient downstate. In the most desynchronized (desynch) states (trials 5 and 6), responses exhibit a small but reliable initial response followed by a return to baseline, with no discernible persistent response.