Brain hesitates in assembling mosaic of motion

Your brain must integrate information from many different neurons in the primary visual cortex to interpret movement. But how does this complicated process work? Richard Born and Christopher Pack of Harvard Medical School report that an area of the brain known as the middle temporal (MT) visual area has a dynamic solution to the problem — first it makes a quick guess, then incorporates more information to create the true picture. Born and Pack measured neuronal responses in alert macaque monkeys that were shown lines moving at different orientations. How the visual part of the brain interpreted the direction of movement could be determined by the firing of direction-selective MT neurons. The team found that the MT initially responded primarily to the perpendicular component of the movement, consistent with the idea that more neurons are registering only this direction. But over a period of about 60 milliseconds, the neurons gradually register the true direction of movement. “The brain makes a very quick guess,” said Born. “It takes time for the right answer to percolate.”