Vernier threshold and the parallel visual pathways in bipolar disorder: A follow-up study

Magnocellular (M) and parvocellular (P) visual pathways participate in the processing of low contrast and colors of objects, respectively. The aim of this study was to investigate M and P pathway functions in bipolar disorder during a depressive episode and after the amelioration of symptoms. Participants (17 patients with type I bipolar disorder and 20 matched healthy controls) received two vernier tasks. During the M pathway test, stimuli were dots with low luminance-contrast (5%), whereas during the P pathway test, isoluminant blue dots were presented against a yellow background. Participants were asked to detect the direction of the horizontal displacement of the dots (left or right). The assessment was performed during a depressive state and during a clinically improved state after 2 months. ⁎⁎⁎During the depressive state, the patients showed significantly impaired M and P pathway functions, whereas during the clinically improved state, their performance was better and was statistically indistinguishable from that of the controls. In conclusion, M and P pathways are impaired in depressed bipolar patients. This deficit is ameliorated along with clinical improvement. Further studies are necessary to separately assess cortical and precortical stages of information-processing, and to exclude the possibility of general motivational and attentional impairments.