Grid-like activity can be seen in the human brain in response to exploring a virtual environment, reports a study published online this week in the journal Nature Neuroscience. These findings imply that our internal navigation system is active even in the absence of movement in physical space.
Previous studies suggest that the sense of place is supported by neurons called place cells, which are active when an animal is in a specific region in an environment, and grid cells that display a spatial pattern of activity that resembles a grid on a map. Though place cells had previously been found in humans, grid cells had been observed only in rodents, bats and monkeys.
Joshua Jacobs and colleagues report evidence for grid-like activity in the human brain, providing the most direct evidence for the existence of grid cells, and suggesting that humans use a coordinate system for navigation similar to that used by other mammalian species. The scientists recorded neuronal activity with electrodes intra-cranially implanted in the brain of patients undergoing treatment for drug-resistant epilepsy. They asked the patients to find objects in a computer-generated virtual environment using a joystick and looked for grid-like features in the recorded activity. In addition to place cell activity in the hippocampus, Jacobs and colleagues found that neurons in the entorhinal and cingulate cortices were active at multiple locations in the environment, forming a lattice covering the entire virtual space. This grid-like pattern strongly resembles the characteristic pattern of activity of grid cells found in animals exploring their physical environment.