The effects on an inhibitory jaw reflex of activating deep somatic aff
erent nerves in a remote part of the body (the arm) were studied in 13
humans. Electromyographic recordings were made from the active masset
er of the long-latency (mean 42.0 +/- 1.1 ms) inhibitory reflex evoked
by electrical stimulation of the upper lip. Immediately after a 1-min
conditioning period during which the participants compressed a hand-h
eld spring once a second while ischaemia was produced in the arm with
an inflated pneumatic cuff, the magnitude of the inhibitory reflex dec
reased significantly (by 43%). The reflex recovered within 5 min to a
magnitude that was not significantly different from its pre-conditioni
ng value. The arm exercise or the ischaemia alone produced no signific
ant changes in the reflex. Furthermore, neither of these last two cond
itions was reported to be painful, whereas the ischaemic exercise prod
uced pain in all but one participant. It is concluded that activation
of remote nociceptive, but not non-nociceptive, deep somatic nerves ca
n modulate jaw reflexes in man. (C) 1997 Elsevier Science Ltd.