to the ubiquitous reference problem for EEG recordings, CSD measures are unique (i.e, identical waveforms for any reference ), and are more closely related to neuronal activity, indicating the strength of underlying current generators as radial (transcranial) current flow (25–26, 29–30). Consequently CSD measures are less likely to be mislocalize activity than their reference-dependent counterparts. Third, CSD measures were quantified using frequency principal components analysis (fPCA) to obtain measures for empirically-derived frequency bands. Using this technique, Tenke and Kayser (29) identified factors with peaks corresponding to alpha subbands, including a high-frequency factor and a low-alpha/theta factor, that included activity typically classified as theta (i.e., between 4–8 Hz). Based on prior findings, we predicted that patients who respond to a serotonin reuptake inhibitor (SRI) would show greater global alpha than nonresponders, and also differ in their alpha asymmetry. Moreover, given evidence that pretreatment EEG theta also predicts antidepressant response (31–34), we examined whether the predicted differences between responders and nonresponders would be most prominent for the low-alpha/theta factor.
