Direct voluntary control of pupil constriction and dilation: Exploratory evidence from pupillometry, optometry, skin conductance, perception, and functional MRI

Lisa V. Eberhardt, Georg Grön, Martin Ulrich, Anke Huckauf, C. Strauch

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

We present a single case who can change pupil size on command with dilation of pupil diameter of around 0.8 mm, and constriction of around 2.4 mm. Using modern pupillometric and optometric techniques in combination with measuring electrodermal activity, various indirect mechanisms possibly mediating this phenomenon were tested: accommodation, brightness, increases in arousal by increased mental effort. None of these behavioral tests could support an indirect strategy as the mode of action, although it seems plausible that the case could have learned to gain control over the pupillary response by decoupling pupil size changes from accommodation and vergence in the near triad: Even at maximal accommodation, the case voluntarily constricted his pupil without changing vergence and could improve visual acuity by >6 diopters. Using task-based functional magnetic resonance imaging we found involvement of brain regions generating and mediating volitional impulses. Changes of the left pupil size were associated with increased activation of parts of the left dorsolateral prefrontal cortex, adjacent premotor areas, and supplementary motor area. It still remains open where these neural signals enter the final pathway, either innervating the pupil's dilator directly, or more indirectly by inhibiting the parasympathetically innervated antagonistic sphincter, and vice versa for constriction. To conclude, so far none of potential – conscious or unconscious – indirect strategies, may it be accommodative or vergence efforts or mental efforts and imaginations, could be observed or inferred to be fully responsible, suggesting direct voluntary control of pupil size in the present case.
Original languageEnglish
Pages (from-to)33-42
Number of pages10
JournalInternational Journal of Psychophysiology
Volume168
DOIs
Publication statusPublished - Oct 2021

Bibliographical note

Funding Information:
We are grateful to Daniel Wieczor (D.W.)'s willingness to support us in this experiment, including his participation in all experiments. We would like to thank Sascha Malz for his great support running the optometric testing of the participant.

Publisher Copyright:
© 2021 The Authors

Keywords

  • Pupil dilation
  • Pupillometry
  • Single case
  • Voluntary control
  • fMRI

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