Task-Related Hemodynamic Responses Are Modulated by Reward and Task-engagement
Hemodynamic recordings from visual cortex contain powerful endogenous task-related responses that may reflect task-engagement distinct from attention. We tested this hypothesis with hemodynamic measurements (intrinsic-signal optical imaging) from monkey V1, while the animals engagement in a periodic fixation task over several hours was varied though reward size, and as animals took breaks. With higher rewards, animals appeared more task-engaged; task-related responses were more temporally precise at the task period (~ 10-20 seconds), and modestly stronger. Surprisingly, 2-5-minute blocks of high-reward trials led to ramp-like decreases in mean local blood volume; these reversed with ramp-like increases during low reward. The blood volume increased even more sharply when the animal shut his eyes and disengaged completely from the task (5-10 minutes). We propose a mechanism that controls vascular tone, likely along with local neural responses, with phasic and tonic components tied to task-engagement.