Our recent work suggests that innocuous somatosensory
activity elicited by a brief electrical stimulus is inhibited
by pain evoked by the same electrical stimulus but not
by pain evoked by continuous heat. These results led to
the hypothesis, tested in the present experiment, namely
that pain only inhibits innocuous somatosensation when
the painful and innocuous stimuli have short durations
and close temporal and spatial overlap. A painful 200-ms
laser pulse did not produce a decrease in the perceived
magnitude of the innocuous electrical stimulus or in the
amplitude of a scalp potential that earlier work suggested
is generated by neurons involved in innocuous somatosensation.
Hence, the pain-related inhibition of innocuous somatosensation
observed in these electrical studies cannot be attributed
solely to the duration or to the temporal and spatial overlap
of the innocuous and painful stimuli. Laser pain did produce
a small increase in the subjective magnitude of the innocuous
electrical stimulus, which the electrophysiological evidence
suggests might be due to a change in the late- but not
the midlatency responses in the central innocuous somatosensory
pathways.