Correlating Sympathetic and Parasympathetic Control of Saccade Behaviour
The autonomic nervous system controls numerous effectors within the human body, working to adapt to changing environments. It is composed of three divisions: the sympathetic, parasympathetic, and enteric nervous systems. Sympathetic and parasympathetic activity have been related to emotion, cognition and behaviour. Sympathetic and parasympathetic influence on behavioural performance has been examined extensively; however, the autonomic modulation of performance in tasks involving distinct voluntary and automatic behaviours has not been directly investigated. Interleaved pro- and anti-saccade tasks (IPASTs) are regularly used to evaluate voluntary and automatic behaviour, respectively. The pro-saccade task requires an automatic visuomotor response whereas the anti-saccade task requires the suppression of an automatic response and the generation of a voluntary response in the opposite direction. We sought to investigate parasympathetic and sympathetic modulation of voluntary and automatic saccade behaviour using an IPAST. Thirty healthy human controls completed five blocks of trials (each block: 40 pro / 40 anti = 8 minutes) over 45 minutes. We explored the relationship between experiment duration, autonomic activity and performance in the context of this task as arousal varied. Eye movements, pupil size, electrodermal activity and electrocardiogram were measured throughout. The consecutive measurement of these peripheral autonomic indices further allowed for the investigation of the role of autonomic drive in their coordination. A clear effect of time-on-task on arousal was present in all three measures with arousal increasing across the first three blocks. This modulation of arousal however, was unrelated to task performance, which was unaffected by block number. Lastly, a task effect on performance was found, replicating previous studies. A task effect on arousal was also demonstrated. The changes in sympathetic and parasympathetic activity underlying this effect however are unclear. These findings suggest that the development of cognitive fatigue is not a concern in the use of the IPAST subtending 45 minutes. Additionally, further investigation of autonomic modulation of performance in the IPAST may contribute to the interpretation and analysis of related fMRI data and its application towards investigations of autonomic dysfunction in various neurological disorders. Moreover, the effects of task and block on arousal demonstrated here warrant further investigation.