Gray colored glasses: is major depression partially a sensory perceptual disorder?

BACKGROUND: Major depression is a neuropsychiatric disorder that can involve profound dysregulation of mood. While depression is associated with additional abnormalities besides reduced mood, such as cognitive dysfunction, it is not well established that sensory perception is also altered in this disorder (aside from in psychotic depression). Recent studies have shown that visual processing, in as early a stage as the retina, is impaired in depression. This paper examines the hypothesis that major depression can involve alterations in sensory perception.
METHODS: A Pubmed literature search investigated several lines of evidence: innervation of sensory cortex by serotonin and norepinephrine; antidepressant drugs and depression itself affecting processing of facial expressions of emotion; electroencephalography (EEG) studies of depressed persons and antidepressant drugs; involvement of the serotonergic 5HT2A receptor in both depression and hallucinogenic drug action; psychotic depression involving sensory distortions; dopamine possibly playing a role in depression; and the antidepressant effect of blocking the NMDA receptor with ketamine.
RESULTS: Data from each of these lines of evidence support the hypothesis that major depression can involve sensory perceptual alterations.
CONCLUSIONS: Loss of interest in one's daily activities and inability to experience pleasure, also known as anhedonia, in major depression may in part be mediated by sensory abnormalities, whereby normal sensory perceptions are no longer present to activate reward circuitry. LIMITATIONS: The data supporting the hypothesis tend to be associative, so further confirmation of the hypothesis awaits additional controlled experiments.