Influence of transcranial magnetic stimulation on pupil size

In 22 healthy subjects, painless repetitive transcranial magnetic stimulati on (rTMS) was used to investigate the role of the cortex in the regulation of pupil size and the influence of TMS on the central autonomic nervous sys tem. RTMS was performed over three brain regions of each hemisphere (fronta l, central, parieto-occipital), over cervical nerve roots and in front of t he ear (sham stimulation) while the size of the pupil was measured by infra red oculography. rTMS always elicited a dilatation of both pupils, with its maximum after approximately 1.5 s and without significant R-L difference i n latency or amplitude of pupillary response. No differential effects were observed for stimulation over different cortex regions of one hemisphere, b ut stimulation over the right central region evoked a larger dilatation of the pupil than stimulation over the left. Pupillary dilatation was larger f or cervical nerve root stimulation (+13.2+/-8.3% (S.D.) of baseline) than f or suprathreshold cortex stimulation (+8.4+/-4.5%, five 10-Hz stimuli). Pup illary dilatation in response to magnetic cortex stimulation appears to ref lect a mainly unspecific activation of the sympathetic system rather than a n activation of a cortical pupillomotor centre. Sympathetic activation foll owing rTMS of the cortex does not limit its experimental and therapeutic ap plication.; (C) 2001 Elsevier Science B.V. All rights reserved.