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Here, we assessed the effects of sleep deprivation (SD) on brain activation and performance to a parametric visual attention task. Fourteen healthy subjects underwent functional magnetic resonance imaging of ball-tracking tasks with graded levels of difficulty during rested wakefulness (RW) and after 1 night of SD. Self-reports of sleepiness were significantly higher and cognitive performance significantly lower for all levels of difficulty for SD than for RW. For both the RW and the SD sessions, task difficulty was associated with activation in parietal cortex and with deactivation in visual and insular cortices and cingulate gyrus but this pattern of activation/deactivation was significantly lower for SD than for RW. In addition, thalamic activation was higher for SD than for RW, and task difficulty was associated with increases in thalamic activation for the RW but not the SD condition. This suggests that thalamic resources, which under RW conditions are used to process increasingly complex tasks, are being used to maintain alertness with increasing levels of fatigue during SD. Thalamic activation was also inversely correlated with parietal and prefrontal activation. Thus, the thalamic hyperactivation during SD could underlie the reduced activation in parietal and blunted deactivation in cingulate cortices, impairing the attentional networks that are essential for accurate visuospatial attention performance.