Contrast suppression was substantially lower for patients with major depressive disorder.
New insight shows cortical contrast suppression is reduced during major depressive episodes, while retinal brightness induction remained intact.
Researchers have previous found that the processing of visual contrast information could be altered in patients with major depressive disorder in several studies during the last decade.
A team, led by Viljami Salmela, PhD, Department of Psychology and Logopedics, Faculty of Medicine, University of Helsinki, behaviorally measured contrast perception in 2 center-surround conditions, assessing retinal and cortical processing to clarify the changes at different levels of the visual hierarchy.
In the prospective cohort study, the researchers examined 111 patients with unipolar depression, bipolar disorder, and borderline personality disorder who had baseline major depressive episodes, as well as 29 control participants.
Using a brightness induction test, the researchers assessed retinal processing, while participants compared the perceived luminance of uniform patches presented on a computer screen as the luminance of the backgrounds was varied.
Using a contrast suppression test, the investigators assessed corticol processing, while participants compared the perceived contrast of gratings, which were presented with collinearly or orthogonally oriented backgrounds.
The researchers found brightness induction was similar for both the patients with major depressive disorder and the control group (P = 0.60; d = 0.115, Bayes factor = 3.9).
However, contrast suppression was significantly lower for patients with MDD than it was for the control group (P <0.006; d = 0.663; Bayes factor = 35.2).
Major depressive episodes involve changes at different levels in the visual processing, hierarchy from retina to cortex and from a practical standpoint, visual contrast tests could serve as a rapid, simple, and noninvasive method to serve as a biomarker for the abnormal processing of visual information in depression.
"What came as a surprise was that depressed patients perceived the contrast of the images shown differently from non-depressed individuals," Salmela said in a statement.
Overall, there was no statistically significant associations between contrast suppression and age, sex, or medication or diagnostic subgroup. At the follow-up period involving 74 patients, the researchers did observe some normalization of contrast perception.
“The reduced contrast suppression we observed may have been caused by decreased retinal feedforward or cortical feedback signals. Because we observed intact brightness induction, our results suggest normal retinal but altered cortical processing of visual contrast during a major depressive episode,” the authors wrote. “This alteration is likely to be present in multiple types of depression and to partially normalize upon remission.”
However, the researchers expect the need for future studies.
"It would be beneficial to assess and further develop the usability of perception tests, as both research methods and potential ways of identifying disturbances of information processing in patients," Salmela said.
An example of this could be using perception tests as an additional tool when assessing the effect of therapies as treatment progresses.
The study, “Reduced visual contrast suppression during major depressive episodes,” was published online in the Journal of Psychiatry & Neuroscience.