Pupil-size asymmetry is a physiologic trait related to gender, attentional function, and personality

Abstract

A small difference in the size of the two pupils is common in healthy individuals, a condition termed benign or physiologic anisocoria (BA). Past research indicates that BA is probably caused by asymmetry in sympathetic nervous system (SNS) function [e.g., Rosenberg (2008). Physiologic anisocoria: A manifestation of a physiologic sympathetic asymmetry. Neuro-Ophthalmology, 32, 147-149]. This study is the first to show that BA varies with psychological factors linked to brain asymmetry and autonomic arousal, including gender, attention, and personality. Males exhibited a more directional BA than females, consistent with greater hemispheric lateralization in males. BA also varied with a self-report measure of attentional function, consistent with evidence of hemispheric asymmetry in visuospatial attention networks. Finally, BA varied with personality traits linked to autonomic arousal. Individuals exhibiting higher Meanness and Boldness, and lower Empathy scores tended to show more directional BA. This link between personality traits and BA may be related to brain asymmetries in autonomic arousal and emotion-related processing. If future studies employing direct measures of lateralized brain activity confirm the link between BA and SNS asymmetries, this new metric may prove useful in discovering new relationships between brain organization and psychological function, and how these relationships vary across individuals.

Pupil size asymmetries are modulated by an interaction between attentional load and task experience

“…In these studies, 5 modulations of pupil size were either measured in only one eye or the pupil sizes were 6 averaged across both eyes. However, to the best of our knowledge, only one study has 7 also investigated whether pupil size asymmetries (i.e., differences in pupil sizes between 8 the left and right eye) are related to attentional processing [2]. In this study [2], 9 self-rated assessments of attention ability significantly correlated with pupil size 10 asymmetries, suggesting that also pupil size asymmetries could be modulated by 11 attentional processing.…”

“…However, to the best of our knowledge, only one study has 7 also investigated whether pupil size asymmetries (i.e., differences in pupil sizes between 8 the left and right eye) are related to attentional processing [2]. In this study [2], 9 self-rated assessments of attention ability significantly correlated with pupil size 10 asymmetries, suggesting that also pupil size asymmetries could be modulated by 11 attentional processing. Such a link between pupil size asymmetries and attentional 12 processing could be explained by the right-lateralization of attentional processing in the 13 brain [33][34][35] and the relation of attentional processing to structures involved in the 14 control of pupil sizes (i.e., the locus coeruleus [14,32,[36][37][38]).…”

“…For all these analyses, we averaged across the pupil sizes for the left and right eye. However, findings of a recent study [2] have suggested that also asymmetries in pupil sizes could be related to attentional processing. Given these findings, we further analyzed our data to investigate to what extent pupil size asymmetries are modulated by attentional load and task experience.…”

Comparison of ocular biometric parameters between concomitant exotropic and orthotropic eyes

“…20% of normal people has physiologic anisocoria with no ocular and neurologic pathology [27,28]. Larger contraction anisocoria appeared when stimulating the right eye and found in males [29,30] which may be caused by brain asymmetry in visual cortices in male and lateralization toward the right hemisphere [31]. The relationship between anisocoria and XT or ocular biometric parameters is less frequently investigated in studies.…”

Identification of attention-deficit hyperactivity disorder based on the complexity and symmetricity of pupil diameter

“…This is caused by overactivity in the locus coeruleus (LC) 21 – 23 , which is a norepinephrine (NE) neural pathway that spans the entire brain and plays a critical role in arousal and attention (reviewed in 24 ). In addition to overactivity of LC, the dysfunction of the right hemispheric LC, which has a crucial role in attention functions 25 , has been pointed 26 . However, it is difficult to measure LC activity directly using EEG because the region is located deep inside the brainstem.…”