The effects of temperature on parameters of motor nerve excitability were i
nvestigated in 10 healthy human subjects. The median nerve was stimulated a
t the wrist and compound muscle action potentials were recorded from the ab
ductor pollicis brevis, Multiple excitability measures were recorded: stimu
lus-response curves, the strength-duration time constant (tau (SD)), thresh
old electrotonus, a current-threshold relationship and the recovery of exci
tability following supramaximal activation. Recordings were made at wrist t
emperatures of 35, 32 and 29 degreesC by immersing the arm proximal to the
wrist in a water-bath, Cooling increased the relative refractory period by
7.8% per degree C (P < 0.0001), slowed the accommodation to depolarizing cu
rrents by 4.0% per degree C (P < 0.0001) and increased tau (SD) by 2.6% per
degree C (P < 0.01), but most other excitability parameters were not affec
ted significantly. The effects of temperature on threshold electrotonus wer
e investigated further in separate studies on two subjects over the range 2
8-36<degrees>C and found to be complex. Whereas the rate of accommodation t
o depolarizing current was closely related to instantaneous temperature, th
e threshold increase induced by hyperpolarizing current was most sensitive
to changes in temperature, probably because warming the nerve causes a tran
sient hyperpolarization by accelerating the electrogenic sodium pump. Conse
quently, it may be preferable to make allowances for differences in skin te
mperature when testing patients for abnormal excitability parameters, rathe
r than to change the temperature to a standard value. For most excitability
parameters, however, temperature control is not as important as it is for
conduction velocity measurements.