P300 component of the event related potential (ERP) provides one neurophysiological index of cognitive dysfunction in depression. Forty subjects fulfilling DSM-III criteria for depression were compared to 40 age and sex matched normal controls. The P300 was recorded using the auditory odd-ball paradigm. Depressives had a significantly prolonged P300 latency and reduced P300 amplitude as compared to the controls. The P300 latency showed a significant positive correlation with age of the patient and severity of depression while P300 amplitude showed a significant negative correlation with age. The clinical subcategory of depression, duration of illness and sex did not show any relationship with P300 abnormality. Twelve out of 40 depressives (30%) had an abnormal P300. The mean Hamilton Rating Scale for Depression (HRSD) score was significantly high in those with an abnormal P300.
