Event-related potentials during mental rotation tasks in patients with first-episode depression

BACKGROUND: The ability to mentally rotate images is impaired in depressed patients but the electrophysiological abnormalities in the brain related to this impairment remain unclear. AIM: To compare the event-related potentials (ERPs) of depressed patients and control subjects during the completion of a mental rotation (MR) task. METHODS: Thirty-two inpatients and outpatients with first-episode depression and twenty-nine control subjects were administered an MR task that presented test stimuli at different angles of orientation. During the test ERPs were measured in four regions of the brain (PZ, CZ, P3 and P4). Outcome variables included the error rate, reaction time, P500 latency and maximum P500 amplitude. RESULTS: Compared to control subjects, patients with depression completing the MR test had a significantly longer mean (sd) reaction time (689 [98] ms vs. 569 [55] ms; t=4.36, p<0.001) and a significantly higher mean percent error rate (30.2% [11.4%] vs. 20.3% [7.2%]; t=3.61, p=0.015); these differences were also significant at each of the four orientation angles assessed. The ERP assessment during the MR test found that patients had a non-significant increase in the overall P500 latency and a significant reduction in the mean maximum P500 amplitude at each of the four brain regions assessed. For both patients and controls the error rate, reaction time, P500 latency and P500 amplitude increased significantly in a stepwise fashion as the angle of orientation of the presented stimulus increased from 0° to 180°. In the control group there was a positive peak in the averaged ERP waveforms at about 700 ms that was not present in the patient group. CONCLUSION: Our study confirms previous work on the usefulness of MR tests to assess the cognitive deficits in depression. We find that the electrophysiological measures provided by ERP assessments during MR tasks, particularly maximum P500 amplitude and maximum P700 amplitude, are potential biological markers for depression. Prospective studies that assess changes in these measures over the course of a depressive illness will be needed to confirm their usefulness.