Israeli researchers understand how the Brains GPS Goes Off the Grid
Posted on: 21/Aug/2021 9:51:24 AM
In a new study published in Nature today, Weizmann Institute of Science researchers, in collaboration with the Hebrew University of Jerusalem, unveiled for the first time how three-dimensional space is represented in the mammalian cortex by the brain’s “GPS” system. The team of researchers, led by Prof. Nachum Ulanovsky of Weizmann’s Neurobiology Department, were surprised to find that this representation is very different from the way in which two-dimensional space is represented, turning several long-standing hypotheses on their heads.
Mammals, including humans, know their position in space, owing to several types of specialized neurons in the hippocampus and its next-door neighbor the entorhinal cortex – regions located deep inside the brain. Head-direction cells, the internal compasses of the brain, indicate to the animal the direction in which its head is turned. Place cells, thought to construct a mental map of the environment, are activated when an animal crosses a specific location. Grid cells, by contrast, respond not to one, but to multiple such locations, and they are thought to provide the brain with a GPS system of sorts.
A study of grid cells and the brain’s GPS was awarded the Nobel Prize in 2014. However, these and other studies focused solely on how two dimensions are represented and said very little about the representation of three-dimensional space. To bridge this gap, Prof. Ulanovsky and colleagues set out to elucidate how grid cells act in three dimensions in freely behaving bats.
In the past, when grid cells were studied in rodents running on two-dimensional surfaces, they were found to be activated in multiple circular areas, known as firing fields, which are arranged in a symmetrical hexagonal pattern – resembling millimeter graph paper – that tiles the surface. This unparalleled symmetry and periodicity suggest that these cells may be involved in geometric spatial computations that form the core of the cerebral GPS. The entorhinal cortex, where grid cells are located, is the brain area that is first affected in Alzheimer’s disease, and it is possible that spatial disorientation, one of the early manifestations of Alzheimer’s, is due to the grid cells’ dysfunction – and the loss of the hexagonal “millimeter paper” of grid cells.
