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

- No directional effects of low arousal on horizontal eye movements.
- Direction-unspecific effect on attentional disengagement induced by low arousal.
- Detrimental effect on peak velocity whereas saccadic reaction times were spared.
- Differential vulnerability of covert and overt attention to variations of arousal.
- Neural non-overlap of brain structures representing covert and overt orienting.

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 4 h over 24 h 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.