The ability to sustain attention over prolonged periods of time is called vigilance. Vigilance is a fundamental component of attention which impacts on performance in many situations. We here investigate whether similar neural mechanisms are responsible for vigilant attention over long and short durations of time and whether neural activity in brain regions sensitive to vigilant attention is related to processing irrelevant information. Brain activity was measured by means of functional magnetic resonance imaging (fMRI) in a 32 min visual vigilance task with varying inter-target intervals and irrelevant peripheral motion stimuli. Changes in neural activity were analysed as a function of time on task to capture long-term aspects of vigilance and as a function of time between target stimuli to capture short-term aspects of vigilance. Several brain regions including the inferior frontal, posterior parietal, superior and middle temporal cortices and the anterior insular showed decreases in neural activity as a function of time on task. In contrast, increasing inter-target intervals resulted in increased neural activity in a widespread network of regions involving lateral and medial frontal areas, temporal areas, cuneus and precuneus, inferior occipital cortex (right), posterior insular cortices, the thalamus, nucleus accumbens and basal forebrain. A partial least square analysis revealed that neural activity in this latter network covaried with neural activity related to processing irrelevant motion stimuli. Our results provide neural evidence that two separate mechanisms are responsible for sustaining attention over long and short durations. We show that only brain areas involved in sustaining attention over short durations of time are related to processing irrelevant stimuli and suggest that these areas can be segregated into two functionally different networks, one possibly involved in motivation, the other in arousal.
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