Effect of sleep deprivation and low arousal on eye movements and spatial attention.

Research on the neural underpinnings of attention repeatedly revealed a predominant role of the right hemisphere for alertness and visuo-spatial attention. Furthermore, previous studies demonstrated an impairment of covert attentional orienting to the left with reduced alertness or time-on-task. However, recent and preliminary evidence suggests that this arousal-dependent attentional asymmetry cannot be observed in overt orienting. Thus, in the present study we repeatedly measured eye movements in experimental paradigms with varying attentional demands repeatedly every 4h over 24h in total in healthy subjects undergoing sleep deprivation. The main focus was the effect of low arousal induced by sleep deprivation on saccadic reaction times and peak velocity to left-sided and right-sided peripheral targets. Overall, we did not find any directional effects of low arousal on horizontal eye movements. By contrast, low arousal led to a direction-unspecific effect on attentional disengagement when a subsequent saccade had to be initiated. Furthermore, a detrimental effect of reduced arousal on peak velocity of saccades was observed whereas saccadic reaction times were mainly spared. Our results point to a neural non-overlap of brain structures representing covert and overt orienting and a differential vulnerability to variations of the norepinephrine system. This also fits with the reported dissociation of stimulus- and goal-driven attentional functions in visual hemineglect.