A RELATIONSHIP BETWEEN BEHAVIORAL CHOICE AND THE VISUAL RESPONSES OF NEURONS IN MACAQUE MT

We have previously documented the exquisite motion sensitivity of neur ons in extrastriate area MT by studying the relationship between their responses and the direction and strength of visual motion signals del ivered to their receptive fields. These results suggested that MT neur ons might provide the signals supporting behavioral choice in visual d iscrimination tasks. To approach this question from another direction, we have now studied the relationship between the discharge of MT neur ons and behavioral choice, independently of the effects of visual stim ulation. We found that trial-to-trial variability in neuronal signals was correlated with the choices the monkey made. Therefore, when a dir ectionally selective neuron in area MT fires more vigorously, the monk ey is more likely to make a decision in favor of the preferred directi on of the cell. The magnitude of the relationship was modest, on avera ge, but was highly significant across a sample of 299 cells from four monkeys. The relationship was present for all stimuli (including those without a net motion signal), and for all but the weakest responses. The relationship was reduced or eliminated when the demands of the tas k were changed so that the directional signal carried by the cell was less informative. The relationship was evident within 50 ms of respons e onset, and persisted throughout the stimulus presentation. On averag e, neurons that were more sensitive to weak motion signals had a stron ger relationship to behavior than those that were less sensitive. Thes e observations are consistent with the idea that neuronal signals in M T are used by the monkey to determine the direction of stimulus motion . The modest relationship between behavioral choice and the discharge of any one neuron, and the prevalence of the relationship across the p opulation, make it likely that signals from many neurons are pooled to form the data on which behavioral choices are based.