Philipp Kreyenmeier¹, Corey M. Ziemba¹, Klaury Youchom-Tagheu¹, A. Tyler Morgan¹, Hendrikje Nienborg¹, Elisha P. Merriam¹; ¹National Institutes of Health

Even in the absence of visual stimulation, early visual cortex (EVC) exhibits hemodynamic responses related to task structure, task difficulty, and arousal state. The origins underlying this widespread response in EVC remain unknown. Here we test whether task predictability or external behaviors modulate the task-related response. Participants performed a rapid serial visual presentation task at the screen center, followed by a resting period during which participants saw the same visual stimuli, but did not perform a task. In Experiment 1, the duration of the rest period was fixed, making the onset of each trial predictable. In Experiment 2, we made the trial onsets unpredictable by varying the rest period from trial to trial. We measured eye movements, heart rate, and respiration, simultaneously with fMRI BOLD responses. Pupillometry, eye movements, and blinks showed a strong periodic modulation at the task frequency. Pupil size increased during the task phase and decreased during the resting phase. Saccades and blinks were suppressed during the task phase and showed a pronounced release during the resting phase. Similarly, the BOLD response over EVC showed a strong periodic modulation at the task frequency. Whereas visually-stimulated foveal regions showed an increase in the BOLD response during the task phase and a decrease during the resting phase, unstimulated peripheral regions showed a later BOLD response peaking towards the end of the trial. This task-related BOLD response persisted when the timing of the task was unpredictable (Experiment 2), and when accounting for the systematic modulations in blink rates. Our findings are broadly consistent with previous imaging studies in monkeys and humans. Extending these earlier findings, we show that neither temporal predictability, nor task-related blinking can account for widespread task-related hemodynamic activity in EVC.