Background:
Major depressive disorder may be a heterogeneous disorder; yet, melancholic depression is the most consistently described subtype, regarded as qualitatively different to nonmelancholic depression in terms of cognitive and motor impairments. Eye movement studies in depression are infrequent and findings are inconclusive.
Methods:
This study used a battery of saccadic (very fast) eye movements to explore reflexive saccades, as well as higher order cognitive aspects of saccades including inhibitory control and spatial working memory. Nineteen patients with major depressive disorder (9 melancholic, 10 nonmelancholic) and 15 healthy controls participated.
Results:
Differences were showed between melancholic and nonmelancholic patients. Melancholia was associated with longer latencies, difficulty increasing peak velocities as target amplitudes increased and hypometric primary saccades during the predictable protocol. In contrast, the nonmelancholic depression group performed similarly to controls on most tasks, but saccadic peak velocity was increased for reflexive saccades at larger amplitudes.
Conclusions:
The latency increases, reduced peak velocity and primary saccade hypometria with more severe melancholia may be explained by functional changes in the fronto-striatal-collicular networks, related to dopamine dysfunction. In contrast, the serotonergic system plays a greater role in nonmel-ancholic symptoms and this may underpin the observed increases in saccadic peak velocity. These findings provide neurophysiological support for functional differences between depression subgroups that are consistent with previous motor and cognitive findings.
