Fig. 4

Effect of VNS on choice. A Schematic representation of the inter-temporal reward choice task. (1) The subject was required to fixate on a red dot presented in the middle of the screen, straight ahead for 350 ms, at which point (2) two fractal images representing the SS and LL were displayed to the left and right of the fixation point while the subject maintained fixation. (3) Upon offset of the fixation point, the signal to respond, the subject was expected to make a saccadic eye movement to one of the two fractal images, indicating his choice. (4) When the eye-tracker detected the subject’s eyes within the acceptance window of one of the images, a large red dot was overlaid on the fractal, indicating to the subject his choice. (5) In this example, the subject chose the SS (left image), in which case the reward was delivered immediately and a 16 s wait would precede the start of the next trial. Conversely, had the subject chosen the LL (right image), a delay of 16 s would have preceded the delivery of the reward and the onset of the next trial would have followed shortly after. Both images remained on the screen for the duration of the delay period. B Discounting values (Kappa) for control and three VNS conditions: VNS paired with stimulus onset, with SS and with LL. In this single session, the value of Kappa was smaller than in the other three conditions, indicating that the NHP was more patient in evaluating his choices