Fig. 1: Foraging in freely moving monkeys while population activity in the prefrontal cortex is recorded wirelessly.

a, Left: schematic of experimental setup with two reward boxes, two buttons and an overhead camera. Right: the ___location of the Utah array in the dlPFC (area 46) and wireless transmitter. b, Press-averaged firing rates of 80 single and multi-units recorded simultaneously. c, An illustration of task dynamics with eight hypothetical presses (vertical lines) in the concurrent variable-interval foraging task. In this illustration, the monkey responds six times on box 1, then switches to box 2 and responds twice. Therefore, press 6 is considered a press with a switch choice. The first two rows show the independent telegraph processes determining the reward (rew.) availability at boxes 1 and 2. In the example shown, press numbers 2, 5, 7 and 8 were rewarded (third row, red). The time dependence of the probability of reward availability is shown in the fourth row (see d for a different representation). d, An alternative illustration to clarify the relationship between the probability (prob.) of reward availability (avail.) and the waiting time. The shaded area shows when a reward is available after each of the 20 presses on box 1 (some of them shown in c). The black trace associated with the y axis on the right shows the probability of reward availability (Methods and Extended Data Fig. 2a), which at each time is in fact the proportion of pink bars, out of 20 trials with pink bars. e, The spike train of one example neuron on the timescale of four consecutive presses showing a variety of events (top row). Event-locked average firing rates of the same neuron are shown in the bottom row for conditions with reward/no reward and stay/switch choices. For ease of visualization, this example used a neuron with a relatively low firing rate compared to others in the population (compared with b).