Third, there was an absence of significantly increased low frequency power in our sample of SZ, a finding that was commonly reported in previous studies (Clementz et al. 1994; Gattaz et al. 1992; Sponheim et al. 1994; 2000). Of note, the mean power values for delta and theta activity were both increased in the SZ group, but this difference did not reach significance. There are several possible explanations that may account for this disparity. First, we assessed power using CSD rather than voltage values. Second, while we employed ICA to correct for artifacts, many previous studies performed traditional threshold-based ocular artifact correction (Clementz et al. 1994; Gattaz et al. 1992; Sponheim et al. 1994). Third, our samples may differ in terms of clinical characteristics from other studies. For example, several previous studies recruited drug-free SZ (Gattaz et al. 1992; Miyauchi et al. 1996), whereas the current study recruited SZ regardless of their medication status but statistically accounted for medication use in analyses. Future studies are necessary to determine whether increased low frequency power is a unique characteristic of schizophrenia or a function of either methodology or medication effects.
