People who suffer from severe depression literally see the world through different eyes, including an enhanced ability to track motion, a new study reveals.
But the illness does not uniformly improve vision: The ability to perceive fine details worsens.
The findings provide a rare insight into how the chemical changes that characterize depression directly alter basic brain functions. Teasing out such specific effects from the large-scale changes that depression causes in mood and thinking is particularly difficult, but may open the door to new ways to test for or treat the disorder.
“It’s striking that the patient group was actually outperforming the control group [in motion tracking],” says study lead author Julie Golomb of the Massachusetts Institute of Technology. “When you see changes in performance on perceptual or cognitive tasks, it’s usually a deficit in performance for the patient population, and that makes it more difficult to interpret. Is the deficit due to the neuropathology of the disorder itself, or is it a byproduct of the symptoms the person is experiencing?”
“[This study] provides us some basic understanding into the experience of a person undergoing a major depressive episode,” adds Lisa Betts, a postdoctoral fellow at McMaster University who was not involved in the new research. “People with depression really do have a different take on the world. The world looks different to them.”
The results, which were published July 15 in the Journal of Neuroscience, came from 16 people with major depressive disorder (MDD) who were not suffering an acute bout of the illness at the time and therefore were not taking any medication.
Compared with healthy volunteers, the MDD group showed a decrease in spatial suppression—a visual processing strategy in the brain in which specialized neurons that respond to adjacent areas of space inhibit one another by releasing the inhibitory neurotransmitter GABA. This process enhances our ability to make out fine details and detect boundaries and edges.
“Imagine if you were watching a hockey game,” Betts says. “There is a continuous flow of moving bodies. If you have a lot of inhibition in the brain, you are going to be able to pick out specific players much more easily, but you’ll be less sensitive to the overall flow of the game.”
The results of the new study, she adds, are particularly exciting because it is among the first to directly track the effects of reduced inhibition in the brain during illness, a technique that has great promise. Researchers have known for some time that GABA levels drop in people with MDD, including in vision-processing areas, and such changes may also play a prominent role in schizophrenia as well as healthy aging.
Golomb and her colleagues also found that the more severe a person’s lifetime history of depression, the less spatial suppression—and therefore the more motion perception ability—they showed. This result suggests that vision changes may serve as a possible diagnostic test for depression or an impending depressive episode.
“Obviously it could never replace a true clinical diagnosis, and a lot more research would be necessary before it gets to that point,” Golomb says. “But it would certainly be exciting if future research demonstrated its utility as a marker for certain risk factors.”
She adds that the changes in vision may serve as a decent proxy for what else is going on in the brain in MDD, offering insights not just into the underlying biology of the disorder but also into potential new treatment options.
“It’s possible,” she says, “that something analogous might be going on [with other depression symptoms] where there is a broader dysfunction in neural inhibition, which could also make it difficult to inhibit negative thoughts.”