Prepulse inhibition of the blink reflex by laser stimuli in normal humans

The subcortical integrative effects of laser-induced activation of pain asc ending tracts were examined in 11 healthy volunteers, aged 22-52 years. Sub jects underwent either CO2 laser stimulation at the dorsum of the hand, ele ctrical stimulation of digital nerves at the 3rd finger, or mechanical taps to the first dorsal interosseous space, preceding a blink reflex elicited by a supraorbital nerve electrical stimulus. The percentage inhibition indu ced in the R2 response of the blink reflex was similar for the three differ ent stimulus modalities, but occurred at a different time interval. Compare d to control trials, the R2 response of the test trials was a mean of 23.1% at the interval of 250 ms with laser stimuli, 17.4% at the interval of 100 ms with electrical stimuli to the 3rd finger, and 20.6% at the interval of 90 ms with a mechanical tap to the Ist interosseous space. Activation of p ain receptors induce prepulse inhibition of the blink reflex at a delay cor responding to a slowly conducting pathway. The percentage inhibition is sim ilar to that observed with other somatosensory inputs. (C) 2000 Elsevier Sc ience Ireland Ltd. All rights reserved.