Effect of DLPFC rTMS on anhedonia and alpha asymmetry in depressed patients

Anhedonia, a core symptom of depression, has been defined as the loss of pleasure or lack of reactivity to pleasurable stimuli. Considering the relevance of alpha asymmetry to MDD and anhedonia, we explored the effect of dorsolateral prefrontal cortex (DLPFC) stimulation on frontal and posterior EEG alpha asymmetry (FAA and PAA, respectively), in this exploratory investigation. 61 participants randomly received sham (n = 11), bilateral (BS; n = 25), or unilateral stimulation (US; n = 25) of the DLPFC. The Snaith-Hamilton Pleasure Scale (SHAPS) was administered. FAA and PAA were calculated by subtracting the natural log-transformed alpha power of the right (F8 or T6) from that of the left (F7 or T5) EEG channel. Furthermore, alpha peak was defined as the frequency where alpha power was at its maximum. BS and US both reduced anhedonia symptoms in the active compared to the sham group. Even non-responders in the BS group showed a decreased anhedonia. Interestingly in the BS group, only the patients who showed a right-lateralized FAA or PAA at baseline showed a reduction in anhedonia. However, in the US group, only patients with left-lateralized FAA or right-lateralized PAA showed a decrease in anhedonia. PAA at baseline predicted symptoms post treatment. Furthermore, a significant positive correlation between baseline alpha peak values and SHAPS scores post treatment were found in the BS group. PAA was a better predictor of anhedonia and reduction of depressive symptoms in both groups. BS may produce larger effects with regard to anhedonia.