Appraisal of sessional EEG features as a correlate of clinical changes in an rTMS treatment of depression

Previous findings on electrophysiological features related to depression predict that these correlate with clinical assessment, and potentially act as proxy measures of state changes, We investigated selected electrophysiological features to evaluate their utility as proxies for clinical ratings and in prediction of treatment outcome. Using typical EEG data from an repetitive transcranial magnetic stimulation (rTMS) treatment regime, we analyzed individual alpha power and frequency, and asymmetry index from 39 patients with treatment resistant depression. The prognostic utility of these features was assessed in terms of group identification, correlation with clinical rating, or association with the time course of treatment. There was no significant group difference in asymmetry between depression patients and normal and clinical controls. Background alpha was significantly less in depression patients than controls, with the schizophrenia group midway between. There was no significant group change in asymmetry index or background alpha activity with treatment. There was a weak effect of rTMS over each session on alpha power and on asymmetry, but in the opposite direction to predictions. There was weak evidence of predicted correlation between asymmetry index change and clinical rating change, as well as in final scores that was opposite to predictions. Finally there was no strong evidence that either feature fitted a linear or more complex model of daily treatment. In conclusion, the findings are not sufficient, under our current clinical treatment regime, to support the use of background alpha activity or frontal asymmetry as proxies for clinical assessment. Several findings, however, provide support for further research in this direction.