The superior colliculus is a region of the midbrain that has traditionally been considered key to helping animals orient to important places in space, such as directing their eyes and head toward a flash of light. However, new research from the University of Chicago reveals that this part of the brain is also involved in complex cognitive tasks, such as visual categorization and decision making.
The scientists measured the information present in the patterns of neural activity in several brain regions involved in visual categorization decisions. Activity was monitored in the superior colliculus (SC) and in a part of the posterior parietal cortex (PPC), an area of the brain important for visual categorization decisions.
Surprisingly, the researchers observed that activity in the SC was even more relevant than in the PPC in guiding subjects’ decisions, suggesting that this area helps coordinate high-level cognitive processes normally associated with the neocortex. . The findings have been published in Nature Neuroscience.
An ancient brain region with surprising capabilities
All animals, from fish and reptiles to mammals such as primates and humans, need to quickly distinguish and categorize objects in their visual field to determine, for example, whether the approaching object is an obstacle or threat, or whether a sudden movement belongs to a predator or prey.
The superior colliculus is a region of the brain that has been evolutionarily conserved in all vertebrates, which helps guide head and eye movements towards visual stimuli, and its main function was believed to be initiating reflex motor actions by transmitting signals from others. regions of the brain. However, recent research has shown that it also participates in more complex tasks, such as selecting an orientation point or paying attention to stimuli in different spatial locations.
When asked what we had for dinner the night before, we often roll our eyes upward, as if the answer were written on the ceiling.
Freedman and his team have been studying for years other cortical areas anatomically connected to the superior colliculus, which are involved in more abstract decision-making tasks. In this new study, they trained monkeys to perform a visual decision-making task in which they looked at images on a screen and received a reward in the form of fruit juice if they managed to assign the images to their corresponding category.
While the subjects performed the task, the researchers recorded neural activity in the CS and in the lateral intraparietal (LIP) area, part of the PPC that Freedman’s lab had already linked to categorization decisions. Since the task required the animals to maintain their gaze at a fixed point and indicate their choices by a hand movement, the experimental design isolated brain activity related to categorization, not eye or head movements, that are traditionally associated with the CS.
The researchers noticed a lot of activity in the superior colliculus related to image categorization, and this activity was even more pronounced than in the CPP. Additionally, they performed an experiment in which they injected a drug to temporarily numb the CS during the same task. Although most motor and visual functions were unaffected, the subjects’ ability to correctly categorize images was drastically reduced 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 do not need to move their eyes or direct their attention to different locations, the superior colliculus is involved in these more complex cognitive behaviors.”
Eye movements and hand gestures to try to remember
Freedman noted that, in addition to being surprising to find this activity in the CS, it might indicate something about why this brain region is involved in such complex tasks. Since it is present in all vertebrates, from the most primitive sharks to modern humans, it was one of the first brain regions to evolve to process visual stimuli and generate corresponding movements. But in this study, it also engages in non-spatial functions. Could this be a sign that spatial processing provides a special boost to problem solving?
Freedman referred to the eye movements and hand gestures that we usually make when we are trying to remember something or make decisions. For example, when we are asked what we had for dinner the night before, we often move our eyes upward, as if the answer were written on the ceiling. Or when we are deciding between two options, we can move our hands up and down, as if they were two sides of a scale.
“Some of this information could be telling us that the reason we make these types of spatial gestures is because the parts of the brain responsible for spatial processing are being recruited to help us perform non-spatial cognitive functions,” said Barbara Peysakhovich, first author of the study. study. Furthermore, we have all experienced the feeling of understanding something better when we see it in a graph instead of reading it in a long text.
“They say a picture is worth a thousand words, even a very simple spatial diagram can convey much more information than we could describe with words.” “It’s as if the brain has created a beautiful mental graph paper that it can use to solve both spatial and non-spatial problems,” Freedman concludes.
