Event-related potentials to task-irrelevant sad faces as a state marker of depression

Negative bias in face processing has been demonstrated in depression, but there are no longitudinal investigations of negative bias in symptom reduction. We recorded event-related potentials (P1 and N170) to task-irrelevant facial expressions in depressed participants who were later provided with a psychological intervention and in never depressed control participants. Follow-up measurements were conducted for the depressed group two and 39 months later. Negative bias was found specifically in the depression group, and was demonstrated as enlarged P1 amplitude to sad faces, which normalized in the follow-up measurements when the participants had fewer symptoms. Because the P1 amplitude recorded at the baseline did not differ between the depression group that recovered and the group that did not recover after the intervention, this brain response did not show potential as a biomarker for treatment response. It could have potential, however, to serve as a state-marker of depression.