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. 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. 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. Using task-based functional magnetic resonance imaging we found involvement of brain regions generating and mediating volitional impulses. When there’s a lot of bright light, your pupils will become smaller. This allows more light into the eyes, making it easier to see. Bright light causes pupil constriction, accompanied by a thinner iris. Pupils tend to become bigger (dilate) in low-light situations. 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. (Image courtesy of the National Eye Institute, National Institutes of. read more increases in arousal by increased mental effort. Using modern pupillometric and optometric techniques in combination with measuring electrodermal activity, various indirect mechanisms possibly mediating this phenomenon were tested: accommodation, brightness. ![]() 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.
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