Human Amygdala Sensitivity to the Pupil Size of Others

Abstract

Stimulation of the amygdala produces pupil dilation in animal and human subjects. The present study examined whether the amygdala is sensitive to variations in the pupil size of others. Male subjects underwent event-related functional magnetic resonance imaging while passively viewing unfamiliar female faces whose pupils were either unaltered (natural variations in large and small pupils) or altered to be larger or smaller than their original size. Results revealed that the right amygdala and left amygdala/substantia innominata were sensitive to the pupil size of others, exhibiting increased activity for faces with relatively large pupils. Upon debrief, no subject reported being aware that the pupils had been manipulated. These results suggest a function for the amygdala in the detection of changes in pupil size, an index of arousal and/or interest on the part of a conspecific, even in the absence of explicit knowledge.

The volatility of the amygdala response to masked fearful eyes

“…Thus, the results are in accordance with findings showing that the amygdala is strongly involved in automatic responding to human eyes per se [Adolphs et al, 2005;Spezio et al, 2007] and specific eye information such as ambiguity [Adams et al, 2003], size of eyes [Demos et al, 2008;Hardee et al, 2008] and gaze [Adams et al, 2003;Akiyama et al, 2007;Hadjikhani et al, 2008;Straube et al, in press]. For example, patients with amygdala lesions show disturbed attention to eye information and impaired attentional cuing effects by eye whites or eye gaze [Adolphs et al, 2005;Akiyama et al, 2007;Spezio et al, 2007].…”

“…For example, patients with amygdala lesions show disturbed attention to eye information and impaired attentional cuing effects by eye whites or eye gaze [Adolphs et al, 2005;Akiyama et al, 2007;Spezio et al, 2007]. Furthermore, consciously not recognized size of the pupil of eyes seems to be able to modulate the activation of the amygdala [Demos et al, 2008]. These findings suggest that the amygdala, besides its role in emotion, is relevant for attending to potentially salient information or ambiguous social signals provided by human eyes.…”

“…One possible reason for this finding is that masked wide eyes, compared to small happy eyes, induce stronger flicker effects and greater ambiguity in the neutral eyes of the mask. The amygdala strongly responds to the amount of ambiguity expressed by eyes but also to subtle changes in the eyes [Adams et al, 2003;Demos et al, 2008]. Thus, even though subjects did not spontaneously report flicker effects, they partially may have used these effects to classify the type of masked eyes in the forced choice experiment.…”

“…This, for example, might induce differential flicker effects *Correspondence to: Thomas Straube, Ph.D., Department of Biological and Clinical Psychology, Friedrich-Schiller-University, Am Steiger 3//1; D-07743 Jena; Germany. E-mail: straube@biopsy.unijena.de in the eye region of the mask, which again possibly influences the response of the amygdala, since the amygdala is strongly involved in the processing of ambiguous information [Davis and Whalen, 2001] and subtle changes expressed in human eyes [Adams et al, 2003;Demos et al, 2008;Straube et al, in press].…”

Effect of Intensity of Dynamic Exercise on Pupil Diameter in Humans

“…Certain implications have been indicated, such as for the amygdala, where memory of emotional reactions is found. It has a function associated with the detection of the pupil size of others (Demos et al, 2008). A pupil diameter dilated during exercise and mental task could play a role for signaling specific or nonspecific arousal to others.…”