Clinical Study Pharmacological Isolation of Cognitive Components Influencing the Pupillary Light Reflex Stuart R. Steinhauer, 1,2 Ruth Condray, 1 and Misha L. Pless 3 1 Biometrics Research Program, 151R, VA Pittsburgh Healthcare System, University Drive C, Pittsburgh, PA 15240, USA 2 Department of Psychiatry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA 3 Leitender Arzt Neuroophthalmologie und Neurologie Augenklinik, Zentrum f¨ ur Neurologie und Neurorehabilitation, Luzerner Kantonsspital, 6000 Luzern 16, Switzerland Correspondence should be addressed to Stuart R. Steinhauer; sthauer@pitt.edu Received 10 February 2015; Revised 27 April 2015; Accepted 28 April 2015 Academic Editor: Suphi Taneri Copyright © 2015 Stuart R. Steinhauer et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Cognitive operations can be detected by reduction of the pupillary light response. Neurophysiological pathways mediating this reduction have not been distinguished. We utilized selective blockade of pupillary sphincter or dilator muscles to isolate parasympathetic or sympathetic activity during cognition, without modifying central processes. Pupil diameter was measured during the light reaction in 29 normal adults under three processing levels: No Task, during an easy task (Add 1), or a difcult task (Subtract 7). At three separate sessions, the pupil was treated with placebo, tropicamide (blocking the muscarinic sphincter receptor), or dapiprazole (blocking the adrenergic dilator receptor). With placebo, pupil diameter increased with increasing task difculty. Te light reaction was reduced only in the Subtract 7 condition. Dapiprazole (which decreased overall diameter) showed similar task-related changes in diameter and light refex as for placebo. Following tropicamide (which increased overall diameter), there was a further increase in diameter only in the difcult task. Findings suggest two separate inhibitory components at the parasympathetic oculomotor center. Changes in baseline diameter are likely related to reticular activation. Inhibition of the light reaction in the difcult task is likely associated with cortical aferents. Sustained sympathetic activity also was present during the difcult task. 1. Introduction Activation of mental and emotional processes is accompa- nied by changes in pupil diameter [1–3]. While most ofen assessed in terms of dilation of the pupil during experi- mental paradigms, another index of central processing has been observed as reduction in the amplitude of the light response. Psychosensory attenuation of the light refex has been observed most ofen during emotional arousal, includ- ing anticipation of aversive stimuli [3, 4]. Te light refex is reduced in patients with anxiety disorders relative to controls [5], and in patients with schizophrenia [6], though the latter fndings are less consistent [7]. Viewing of pictures matched for brightness indicated that the light reaction was signif- cantly attenuated when comparing afective stimuli (violent or erotic scenes) as compared to neutral scenes [8]. Motor activity also has been demonstrated to reduce the extent of the light reaction [9]. Reduction of light refex amplitude during cognitive operations also has been demonstrated. Subjects required to predict the occurrence of equiprobable sound and light stim- uli exhibited smaller light reactions than under conditions of certainty [10]. Using a mathematical challenge task during presentation of light stimuli, initial pupil diameter increased, and the amplitude of constriction to light decreased [11]. Within the same session, a nonchallenging mathematical task that also required verbalization evoked an intermediate increase in overall diameter, but no reduction of the light reaction. Te central mechanisms that contribute to these changes can be identifed as emanating from specifc sympathetic or parasympathetic pathways [12]. Increases in diameter are Hindawi Publishing Corporation Journal of Ophthalmology Volume 2015, Article ID 179542, 7 pages http://dx.doi.org/10.1155/2015/179542