Functicnal significance of the medial paiietal areas for the cognitive map and navigation

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A cognitive map is a stored representation of a large-scale environment in the brain. When we behave in a large-scale environment, a cognitive map is necessary but not sufficient ; because it is too abstract to plan a specific route map for our navigation. When we drive to our office, we can take the correct route subconsciously, making a turn or going straight at each intersection. This phenomenon suggests we may have an internal list of what we have to do at a given location in addition to a "cognitive map" in our brain. This internal list is known as "route knowledge" and is accessed to be able to navigate ourselves in a large-scale environment. Lesion and neuroimaging studies of humans suggest that the medial parietal region (MPR), including the retrosplenial and posterior cingulate cortices, is critically involved in navigation based on route knowledge. To study the neural mechanisms of navigation in a large environment in primates, a large environment within the experimental setu … More p needs to be built. In this study, we used a virtual reality technique to overcome this problem and recorded a single unit activity from the monkey MPR while the monkey navigated in the virtual environment without performing any actual movement.To examine the neural basis of route knowledge by which one can reach one's destination, we recorded the activity of 580 neurons in the monkey medial parietal region (MPR) while monkeys actively navigated through a virtual environment. One hundred eighty of these neurons (31%) showed significant responses to the monkeys' movements in the virtual environment. Of these responsive neurons, 77% (139-180) showed responses associated with a specific movement at a specific location (navigation neurons), 8% (14-180) showed responses associated with a specific movement (movement- selective neurons), and the remaining 27 neurons (15%) were nonselective. We found navigation neurons whose responses to the same movement at the same location were modulated depending on the route that the monkey was currently taking, that is, in a route-selective manner (32 of 59 tested neurons among 139 navigation neurons, route-selective navigation neurons. The reversible inactivation of MPR neurons by muscimol resulted in a monkey becoming lost during the navigation task trial. These results suggest that MPR plays a critical role in route-based navigation by integrating location information and self-movement information. Less