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By studying the movement of virtual animals in computer simulation, a research team led by Srinivasa Chakravarthy, Department of Biotechnology, at IIT Madras has unlocked the navigation behaviour in rats moving in two dimensions and bats (3D). They hope to use these clues in engineering autonomous vehicles and drones. Previous studies have shown that certain regions (hippocampus and parahippocampus) in the rat brain contain special cells known as “spatial cells” that help to create a cognitive map for navigation. The 2014 Nobel Prize in Physiology or Medicine was awarded to three scientists who discovered cells that constitute a positioning system in the brain. The inner GPS in the brain or the neurons help in coordinating the position, distance and direction of travel. Using mathematical models and computer simulations, the researchers looked at these various spatial cells when rats move along the maze. One of the cells known as ‘place cells’ gets activated when the rat is at a certain place in a room and another type of cells called ‘grid cells’ coordinate this system and help in positioning and pathfinding. “We developed a hierarchical neural network that simulated the neural GPS system reported from the brain of a bat during its flight in 3D space. The network not only explained the formation of 3D place cells but also predicted the existence of novel and yet undiscovered types of spatial cells that could potentially code for 3D space,” explains Karthik Soman from the Department of Biotechnology, IIT Madras, and first author of the paper published in Nature Communications. One such spatial cell predicted from the computer model is a ‘plane cell’ that fires when the animal crosses a plane in 3D space. Another spatial cell predicted is a ‘stack cell’ that fires when the animal flies around multiple planes. As bats are the only flying mammals, Michael Yartsev, one of the authors of the paper, and his group at the University of California Berkeley, further examined bats and the spatial cells in their brain while flying in a 3D space. Using wireless technologies, his group was able to monitor bats’ brain activity when they fly around and was able to show the functioning of the place cells in real animals. “We are now conducting more experiments on bats to check for more 3D spatial codes in the brain. We are looking forward to studying how brain processes large-scale navigation which we do seamlessly in our day-to-day life,” adds Dr. Soman. The researchers hope that an understanding of the spatial navigation system in the brain can also help in engineering automobiles, drones, and underwater vehicles.
