Primary visual cortex linked to action timing

The brain regulates nearly everything about us — homeostasis, perception and cognitive function — but how specific brain regions connect and work together is still not perfectly understood. Recently, a team at the Johns Hopkins School of Medicine and the University of Texas-Houston uncovered a previously unknown role of the region that initiates the processing of visual input. The brain’s primary visual cortex, referred to as V1, is responsible for sensing visual information about the world around us. The primary visual cortex, located in the occipital lobe at the back the brain, creates a map of our visual field. This map is then relayed to other areas of brain, which make decisions based on these visual clues and generate a motor response. This is the traditional or canonical view. However, a recent study conducted by Dr. Marshall Shuler and his team implicates the V1 region in more than just visual sensing. The work, published in Neuron, suggests that the V1 primary visual cortex plays a role in making time-based action decisions following visual stimuli. Shuler is an assistant professor within the department of neuroscience at the School of Medicine. In order to investigate the role of V1 in time-based action, Shuler’s team used mice fitted with a special set of goggles capable of presenting a visual stimulus in the form of light and thereby stimulating the V1 region. The mice, thirsty from a lack of water, were given access to a waterspout. Water would flow from the spout at a specific time interval following a light stimulus that was presented in the goggles. Licking the waterspout in the target interval gave the mice a small amount of water as a reward. However, if they timed it incorrectly, they would receive no water. The researchers then investigated whether mice were capable of being trained to receive the most water. That is, could mice learn to wait and time their licks to get the most water after V1 cortex stimulation by visual cues? This allowed the researchers to test the role of the V1 cortex in making time-based action decisions. The team found that mice could indeed be trained to receive the maximal amount of water. With increased trials, the mice gradually learned to time their licks in order to receive the greatest amount. But this result does not relate the V1 cortex to time-based action. In order to test the role of V1 in time-based action making, they measured the activity of V1 neurons during the same waterspout activity. Shuler and his team found that there was a “trial-by-trial correlation between the neural representation of the interval and the action” in 77 out of the 122 neurons they measured. That is, longer V1 neural firing indicated a longer delay between the visual stimulus and the mouse licking the waterspout. But this correlation was only present when mice were given a visual stimulus. In cases of a non-visual stimulus (such as nose-poke entry), there was no such correlation between neural activity and action. This showed that the V1 region may indeed be regulating time-based action following a visual stimulus. The researchers next tried to optogenetically stimulate V1 neurons, seeing whether it was possible to influence the mice’s behavior by presenting different signals to the V1 cortex. Optogenetics, a relatively new development in the field of neuroscience, enables researchers to stimulate genetically-altered neurons with light. Upon optogenetic stimulation of V1 neurons, the researchers found that he was able to change the waiting time in visually stimulated mice. Consistent with his neural activity findings, they found no change in the non-visually stimulated mice upon optogenetic perturbation. The results suggest that the V1 primary visual cortex, traditionally thought of as being the primary visual sensory area in the brain, may actually play a far larger role in making decisions and performing time-based actions. His findings expand our traditional view of the brain as a compartmentalized organ, with each region having a specific function.