Ž . International Journal of Psychophysiology 39 2000 2130 Cognitive modulation of midbrain function: task-induced reduction of the pupillary light reflex Stuart R. Steinhauer a,b,  , Ruth Condray a,b , Annette Kasparek b a Biometrics Research Program, 151R, VA Pittsburgh Healthcare System, 7180 Highland Dri  e, Pittsburgh, PA 15206, USA b Department of Psychiatry, Uni  ersity of Pittsburgh School of Medicine, Pittsburgh, PA 15206, USA Received 2 March 1999; received in revised form 31 March 1999; accepted 4 April 2000 Abstract The activation of processing resources has widespread effects in the nervous system. A model of pupillary control Ž systems Steinhauer S.R., Hakerem G., 1992. The pupillary response in cognitive psychophysiology and schizophrenia. . Ann. N.Y. Acad. Sci. 658, 182  204 had predicted that ongoing cognitive activation should result in inhibition of the light reaction at the level of the oculomotor nucleus, n. III, in the midbrain. In this study, modification of parameters of the pupillary reaction to light were examined during varying task demands. The averaged light reaction was recorded from 33 male and female healthy volunteers during the performance of a serial 7 subtraction task and Ž compared to a ‘no task’ condition. For 13 subjects, an additional verbalization task with little processing demand add . 1 also was presented. Two types of effects were observed. Firstly, the tonic pupil diameter increased from the no Ž . Ž . task to the easy add 1 task, and increased further in the more demanding condition subtract 7 . Secondly, the extent of the phasic light reaction was significantly reduced and the latency at the end of the contraction was Ž significantly decreased in the ‘subtract 7’ condition compared to both the no task and easy conditions which did not . differ from each other . The locus of interference with the light reaction was the Edinger  Westphal complex of the oculomotor nucleus, which is the motor center for the pupillary sphincter muscles. Descending cortical influences inhibited the activity of the Edinger-Westphal complex. Thus, increasing activation had a tonic inhibitory effect on  Corresponding author. Tel.: 1-412-365-5251; fax: 1-412-365-5259. Ž . E-mail address: sthauer@pitt.edu S.R. Steinhauer . 0167-876000$ - see front matter  2000 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 1 6 7 - 8 7 6 0 00 00119-7