Somehow, when you get out of bed in the middle of the night, you manage to remember where the end of the bed is, how far it is to the bathroom and where the light switch is. You have developed a complex spatial memory of your house, and our brains are filled with countless other spatial maps (maybe some of us have fewer….cough, cough). How exactly does your brain encode this specific spatial information?
It turns out that is it using cells called grid cells, which work much like their name suggests. These neurons are spread out in a grid pattern in your brain and will generate an electrical spike in a pattern related to the direction you are moving. While this has been known about rats, mice and bats it has only recently been confirmed in humans. While fMRI experiments have suggested the existence of such cells, the only way to confirm that individual cells are spiking in response to a directional task is to make electrical recordings from them.
This new study is able to confirm the existence of these cells by making electrical recordings from single cells in human brains. 14 patients were recruited for this study because they were already receiving treatment for drug-resistant epilepsy and had electrodes implanted in their brain as part of their treatment. The patients used a virtual reality device to navigate to the location of a visible or hidden object. Meanwhile, electrical recordings were made and uncovered a specific grid-like spiking of cells that changed depending on which direction the patient was navigating.
Often in neuroscience, cells or phenomena such as this are found in many model systems but it can be problematic or unethical to determine whether the same cells or phenomena exist in humans. This is an exciting example where these patients were able to greatly contribute to basic neuroscience knowledge by agreeing to play a virtual reality game.