Pupillary response to noxious stimulation was investigated
in men (n = 11) and women (n = 9). Subjects
experienced repeated trials of noxious electrical fingertip
stimulation at four intensities, ranging from faint to
barely tolerable pain. Measures included pupil dilation
response (PDR), pain report (PR), and brain evoked potentials
(EPs). The PDR began at 0.33 s and peaked at 1.25 s after
the stimulus. Multivariate mixed-effects analyses revealed
that (a) the PDR increased significantly in peak amplitude
as stimulus intensity increased, (b) EP peaks at 150 and
250 ms differed significantly in both amplitude and latency
across stimulus intensity, and (c) PR increased significantly
with increasing stimulus intensity. Men demonstrated a
significantly greater EP peak amplitude and peak latency
at 150 ms than did women. With sex and stimulus intensity
effects partialled out, the EP peak latency at 150 ms significantly
predicted PR, and EP peak amplitude at 150 ms significantly
predicted the PDR peak amplitude.