This suggests that the changes across conditions in the reliability of slow dynamics (Figures
7A and 7B) are not driven by differences in low-level properties (e.g., the audio envelope; Figure S5) of the stimuli. Slow (<0.1 Hz) fluctuations in population activity are a ubiquitous feature of neural dynamics, but their functional role is uncertain (Bullmore et al., 2001; He, 2011; He et al., 2010; Leopold et al., 2003; Nir et al., 2008; Weisskoff et al., 1993; Zarahn et al., 1997). We mapped the TRWs of human cortical regions using ECoG and tested whether regions with shorter and longer TRWs differ in their slow dynamics. Consistent with fMRI studies (Hasson et al., 2008; Lerner et al., 2011), the electrophysiological measurements revealed that TRWs increased from sensory toward higher order cortices. Notably, regions with longer TRWs exhibited relatively more slow fluctuations and greater temporal autocorrelation, even during resting fixation. Although the slow fluctuations LY294002 solubility dmso were observed in the absence of any stimulus, they became time-locked to the content of audiovisual movie stimuli. Moreover, the slow timecourses were highly reliable in response to movie clips that contained long-range contextual information structure, but they were significantly less reliable in response
to movie clips that had been scrambled. The relationship between long TRWs and slow fluctuations of power was observed regardless of whether the slow fluctuations were measured during Z-VAD-FMK in vivo the intact
or scrambled movie clips (Figures 6C, 6D, 6F, and 6G) or during a fixation period (Figures 6E and 6H). In addition, the LowFq and ACW values were highly correlated across states of fixation and movie viewing (Figure S6). These data suggest that the dynamic timescale in each region is determined in part by circuit properties which shape dynamics in a similar way, regardless of the state of external stimulation. This finding is also consistent with the idea that sensory circuits, which tend to have shorter TRWs, are optimized for rapid transient responses to the environmental state, while higher order circuits, which tend to have longer TRWs, more readily maintain and accumulate information over time (Huk and Shadlen, 2005; Ogawa and Komatsu, 2010; Romo et al., 1999; Shadlen and Newsome, Vasopressin Receptor 2001; Wang, 2002). Although the regional ordering of dynamic timescales was well-preserved across states of task and fixation, the dynamic timescales in individual electrodes did change across conditions. Both short TRW and long TRW regions exhibited relatively more slow fluctuations of broadband power during the intact than during the scrambled stimuli (Figures 6A and 6B). Electrodes with short TRWs responded to low-level stimulus properties such as the audio amplitude (Figure 4A), which changes more rapidly in the scrambled condition (Figure S5). Thus, the change in slow fluctuations in short TRW areas may be attributable to changes in low-level stimulus properties.