[Generalized nocifensive reflexes. I. Methodologic bases]

Normal protective and defence reflexes show that the nocifensive system is intact. Nocifensive reflexes can be modified by various brainstem disturbances, and in the case of lesions the symptoms may appear in the afferent or efferent section of the reflex arc. The purpose of our study was to find a method for evoked generalized nocifensive reflexes so that inferences regarding the course of the reflex could be drawn from a reflex pattern obtained from the latent periods of various lead regions during nocifensive stimulation. The stimulus is provided by a painful train of electrical pulses applied to a superficial nerve (N. medianus, N. fibularis). As a rule, the leads are connected symmetrically to the flexors of the upper and lower extremities. The results shown, as expected, that nocifensive reactions fulfill the conditions of a conditioned reflex with increasing habituation and sensitization. The reflex arc passes through the formatio reticularis, and it is here in particular that cerebral influences can have a modulatory effect. These conclusions are based on the length of the latent times, which are longer than those associated with spinal reflexes, but shorter than the reaction times shown by the voluntary innervation. Moreover, the reflex patterns observed for the upper and lower extremities are identical for different stimulation sites, so the reflex circuit must be supraspinal. Since, in addition, the reflex pattern associated with acoustic stimulation is similar to that of an electrically evoked reflex, the formatio reticularis can be considered a nocifensive centre.