The region of the brain that controls eye movements also plays an important role in higher cognitive functions

The superior colliculus is a region of the midbrain traditionally thought to help animals orient to important locations in space, such as directing their eyes and heads toward a flash of light. New research from the University of Chicago shows that this part of the brain also plays a role in complex cognitive tasks like visual categorization and decision making.

In the study published in Neuroscience of NatureThe scientists measured the information contained in the activity patterns of brain cells in several brain regions involved in visual category decisions. The researchers monitored activity in the superior colliculus (SC) and part of the posterior parietal cortex (PPC), a region of the cerebral cortex that is important for visual category decisions.

To their surprise, they found that activity in the SC was even more involved than in the PPC in guiding subjects’ category decisions, suggesting that it helps coordinate higher-order cognitive processes traditionally thought to take place in the neocortex.

“This is a really surprising place to find these kinds of cognitive signals, because this area of ​​the brain is traditionally associated with simpler spatial orientation behaviors and even reflexive functions,” said David Freedman, Ph.D., professor of neurobiology and the UChicago Neuroscience Institute and senior author of the new study.

“We have this evolutionarily ancient brain structure that appears to be even more involved in complex cognitive decisions than the cortical areas we studied in our experiments.”

An ancient region of the brain with surprising powers

All animals, from fish and reptiles to mammals like primates and humans, must quickly distinguish and classify objects in their field of vision. Is the object heading toward them an obstacle or a threat? Is the object speeding past a predator or prey?

The SC is a brain region that has been evolutionarily conserved in all vertebrates, even those that lack a more sophisticated neocortex. It helps direct head and eye movements to visual stimuli, and was traditionally thought to trigger reflex motor actions by relaying inputs from upstream brain regions.

However, recent research has shown that it is also involved in complex tasks such as selecting an orientation point and paying attention to stimuli located at different locations in space.

Freedman and his team have been studying other cortical areas that are closely related to the cerebral cortex for years. These adjacent areas are involved in flexible and cognitively demanding decision-making tasks, and the researchers wanted to see if the cerebral cortex is also involved in more abstract thinking.

For this latest study, they trained monkeys to perform a visual decision-making task in which they looked at images on a computer screen. The animals were rewarded with fruit juice when they pressed a button at the right time to assign the images to the correct categories.

As the subjects performed the task, the researchers recorded brain cell activity in the SC and the lateral intraparietal area (LIP), a part of the PPC that Freedman’s lab had previously shown to be involved in category decisions during such tasks.

Because the task required subjects to maintain their gaze on a single location and indicate their choices with a hand movement, the experimental design isolated the brain activity needed for categorization, not the eye or head movements usually thought to be the work of the SC.

The researchers observed strong activity in the SC that encoded the categories of images the animals were looking at, and this activity was more intense than in the PPC. They also conducted an experiment in which they injected a drug to temporarily numb the SC during the same task. Although this did not impair most of the subjects’ motor and visual functions, it significantly affected their ability to correctly categorize the images until the effects of the drug wore off.

“Our results show that this area is really important for the task,” Freedman said. “Even in tasks where animals don’t need to move their eyes or direct their attention to different locations, the superior colliculus is involved in these more complex cognitive behaviors.”

That special “punch” for problem solving

According to Freedman, it’s not only surprising to find this activity in the SC; it could also explain why this brain region is called upon to solve such complex tasks. Present in all vertebrates, from primitive sharks to modern humans, it was one of the first brain regions to evolve to help process visual input and generate corresponding movements.

But in this new study, it is also implicated in decidedly non-spatial functions. Could this be a sign that spatial processing gives a special “oomph” to problem solving?

Freedman pointed out the kinds of eye and hand movements humans make when asked to remember something or make a decision. If someone asks you what you had for dinner last night, for example, your eyes often move upward, as if the answer were written on the ceiling. Or when you’re weighing a decision between two choices, you might move your hands up and down like two sides of a scale.

“Some of these data might tell us that the reason we do these kinds of spatial gestures and eye movements is that the spatial parts of the brain are recruited to help us perform these nonspatial cognitive functions,” said first author Barbara Peysakhovich, Ph.D., a former graduate student in Freedman’s lab and now a postdoctoral researcher at Harvard.

We’ve all struggled to understand something written in text (like a long press release about a neuroscience study), only to immediately understand when the same information was presented graphically.

“They say a picture is worth a thousand words. Even a very simple spatial diagram can quickly convey far more information than can be described,” Freedman said. “It’s as if the brain has created this beautiful mental graph paper that it can use to solve both spatial and nonspatial problems.”