Memory of virtual environment and neural mechanism of route learning

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To investigate neural basis of the cognitive map, the representation of the spatial layout of environments, we trained two Japanese monkeys to perform navigation task in virtual building and recorded neuronal activity in the mesial part of the parietal cortex, area 7m and its vicinity. A virtual building with two floors was created by computer graphics and projected stereoscopically on the 100 inches tangential screen by two liquid crystal projectors. 1.Behavioral aspect : The monkey was trained to navigate from a starting point to a goal room out of its direct view by operating a joystick. As the cue of memory guided navigation, the image of the goal room was presented at the beginning of each trial. The monkeys had learned the routes to 5 goal rooms. After learning the task from the first starting point, they were trained to perform the navigation task from a second starting point which is already familiar to them during the first training session. The second training was completed faster than the first one. Furthermore, we found that the time required for a free-way-finding test from a novel starting point was shortened after the second training. 2.Neuronal aspect : We recorded 364 neurons in the mesial parietal cortex and analyzed correlation between the neuronal activity and several task events. Of the recorded neurons, 150 (41%) responded to at least one of three movements, and 56 (15%) showed movement selectivity, changing their activity depending on the type of the movement. Of the movement-selective neurons, 42 (75%) showed location selectivity, changing their responses to the movements depending on the location in the virtual environment. These neurons became active when the monkey made a specific movement at a specific location and may represent important information to follow a route to a destination.