Alteration of the motor response to an acute painful stimulus during tonic immobility

RESUMO

The motor responses caused by liminal (1.0 and 3.0 mA, applied for 3 s) and subliminal electrical stimuli (40 below the liminal value) applied to the dental pulp of the upper incisors of adult guinea pigs (N = 41) are more intense during tonic immobility (TI) than in control situations. Tonic immobility is a temporary state of profound motor inhibition elicited by some form of physical restraint in our experiment induced by maneuvers of lateral postural inversion and movement restraint. This suggests the occurrence of hyperalgesia in the trigeminal territory in situations of direct confrontation with a predator, as in the case for tonic immobility. This hyperalgesia may protect in a reflex manner vital regions of the head and neck from fatal bites inflicted by the predator, but without interrupting the state of immobility, since in our experiments the electric stimuli had no disruptive effect on TI episodes.