Cholinergic-related pupil activity reflects level of emotionality during motor performance.

Pupil size covaries with the diffusion rate of the cholinergic and noradrenergic neurons throughout the brain, which are essential to arousal. Recent findings suggest slow pupil fluctuations during locomotion are an index of sustained activity in cholinergic axons, whereas phasic dilations are related to the activity of noradrenergic axons. Here we investigated arousal due to movement to actively control music (singing) and swaying to music, hypothesizing that actively engaging in musical behavior while singing and moving along to the music will more strongly engage participants emotionally and lead to a qualitatively different pattern of tonic and phasic pupil activity. A challenge in the analysis of pupil data is the turbulent behavior of pupil diameter due to exogenous ocular activity commonly encountered during motor tasks and the high variability typically found between individuals. To address this, we developed an algorithm that adaptively estimates and removes pupil responses to ocular events and a functional data methodology derived from Pfaffs' generalized arousal that provides a new statistical dimension in how pupil data can be interpreted according to putative neuromodulatory signaling. We found that actively engaging in singing enhanced slow cholinergic-related pupil dilations, and having the opportunity to move your body while performing amplified the effect of singing on pupil activity. Phasic pupil oscillations during motor execution attenuated in time, which often is interpreted as a measure of sense of agency over movement.