Saccadic foraging reveals mechanisms of value-based decision-making in primate superior colliculus

Much progress has been made in understanding the neural basis of value-based decision-making using two-alternative forced-choice tasks. A limitation of these tasks is that the value of each option is often confounded with other cognitive factors (e.g. attention/choice probability/motor preparation). To overcome this limitation, monkeys were trained to use gaze to forage among many visual targets of varying value while neurophysiology was conducted in the saccade control center superior colliculus (SC). Surprisingly, each targets value was represented in the SC predominantly in an absolute manner, that is, irrespective of the value of other available items. After fixating a target, the next choice was quickly selected once neural activity rose to a provisional selection level. This selection level systematically decreased, not as individual targets were harvested, but only after a class of value items was completely depleted. Our results reveal the exquisite balance across SC activities that transform value to choice.