Habituation to bearable experimental pain elicited by tooth pulp electrical stimulation.

Stimulation (1/10 sec, 1-2 msec) of the tooth pulp of volunteers was carried out for 120 min at an intensity that produced bearable pain. Cortical evoked potentials, electroencephalographic activity, electromyograms of the superciliary and masseter muscles and galvanic skin response were recorded. Every 30 min, without suspending the stimulation, the subjects were questioned with respect to the sensations accompanying the stimuli. A progressive decrease in all polygraphic responses was observed which coincided with a decrease in the reported sensation of pain. This effect could be reversed by applying heterosensorial stimulation (questioning). It is suggested that this is a phenomenon of habituation to pain since dishabituation, potentiation of habituation, and habituation to dishabituation were found.