That means the firing rate of a cell varies depending upon the direction someone intends to move his or her hand. Movements in a cell's preferred direction correspond to its highest firing rates, while movements in the opposite direction correspond to its lowest firing rates. In a population of many motor cortex cells, many preferred directions are represented. For example, Kipke explains that research results indicate that if the hand moves up and to the right, then the cells whose preferred direction is in that direction will have the highest firing rates. Other cells will have lower firing rates that depend on how far the movement direction deviates from the cell's preferred direction.
Researchers monitor the firing rates of many cells at the same time.
They know their preferred directions. As a result, the scientists are able to predict where the hand will move before the actual movement. Kipke concedes that the data compiled to date is not perfect enough to calculate the exact fingertip position. He also admits that mapping has been hampered by problems in maintaining solid connections between all 96 electrodes and their surrounding cells. Still, he says, what he and his ASU colleagues have learned is sufficient enough to at least establish the hemisphere of motion.