Dysfunction of Preattentive Visual Information Processing Among Patients with Major Depressive Disorder

Background: Major depressive disorder (MDD) is a mental disorder characterized by depressed mood and inability to experience pleasure. Mismatch negativity (MMN) has been established as a correlate of preattentive change detection. In this study, preattentive processing of visual information in MDD patients was investigated using visual MMN (vMMN), and an abnormal vMMN was predicted in depressed patients relative to healthy participants because of dysfunction at the preattentive level. The processes underlying vMMN in MDD patients were also explored, and memory-based comparison preattentive processing was hypothesized to be impaired in MDD patients. Methods: Subjects included 14 medication-free patients (41.4 +/- 12.6 years) with a DSM-IV diagnosis of MDD and 14 age-matched healthy volunteers (41.7 +/- 17.5 years). vMMN was investigated using event-related potentials. The protocol used both an equiprobable sequence and a traditional oddball sequence, and three kinds of difference waves (i.e., deviant-minus-standard, deviant-minus-control, and control-minus-standard) were investigated. Mean amplitudes and peak latencies were subjected to repeated-measures analysis of variance. Results: Although MDD patients showed no reduction in the oddball-vMMN (deviant-minus-standard), they showed a significantly decreased deviant-minus-control difference waves and a trend for an increased control-minus-standard difference waves compared with healthy participants. Conclusions: These data provide evidence for anomalous preattentive information processing in MDD patients. In particular, the abnormality may be due to an attenuated memory-based comparison process and an enhanced refractory process.