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Journal of Ophthalmology
Volume 2015 (2015), Article ID 179542, 7 pages
Clinical Study

Pharmacological Isolation of Cognitive Components Influencing the Pupillary Light Reflex

1Biometrics Research Program, 151R, VA Pittsburgh Healthcare System, University Drive C, Pittsburgh, PA 15240, USA
2Department of Psychiatry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
3Leitender Arzt Neuroophthalmologie und Neurologie Augenklinik, Zentrum für Neurologie und Neurorehabilitation, Luzerner Kantonsspital, 6000 Luzern 16, Switzerland

Received 10 February 2015; Revised 27 April 2015; Accepted 28 April 2015

Academic Editor: Suphi Taneri

Copyright © 2015 Stuart R. Steinhauer et al. This 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 difficult 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 difficulty. The light reaction was reduced only in the Subtract 7 condition. Dapiprazole (which decreased overall diameter) showed similar task-related changes in diameter and light reflex as for placebo. Following tropicamide (which increased overall diameter), there was a further increase in diameter only in the difficult 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 difficult task is likely associated with cortical afferents. Sustained sympathetic activity also was present during the difficult task.