Cardiovascular correlates of arousal and their relationship to saccadic behavior
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Understanding the effect of subject arousal on saccadic behavior can shed light on the mechanisms by which arousal influences executive and oculomotor systems. Increased vagal activity is a key component of the parasympathetic response, and is inversely associated with arousal. We designed two experiments to examine the relationship between saccadic reaction times (SRTs) and two cardiovascular correlates of vagal activity: heart rate (HR) and the normalized high-frequency (HFν) component of heart rate variability (HRV). In the first experiment, 11 normal human subjects performed a simple saccade task where they were asked to shift their gaze towards an eccentric target. In the second experiment, 19 subjects performed a counterbalanced and interleaved task where they were asked to look either towards (prosaccade) or away from (antisaccade) a visual stimulus. Experiment #1 aimed to probe the role of arousal on automatic oculomotor mechanisms, while Experiment #2 added an executive component. On the basis of data from these experiments, we propose the existence of two discrete mechanisms: a parasympathetic pathway that modulates automatic functions on a 25-minute timescale and another that modulates both executive and automatic functions on a 2 min timescale. We also postulate a mechanistic hypothesis for the neurovisceral integration of arousal, oculomotor behavior and cardiovascular parameters. These findings may allow concurrent pulse oximetry to be used for improving the fidelity of future oculomotor and other neurophysiological experiments.