SUR UN PHÉNOMENE DE FACILITATION RÉTROACTIVE DANS L’ÉXCITATION ÉLECTRIQUE DE BRANCHES NERVEUSES CUTANÉES (SENSIBILITÉ TACTILE)

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Abstract
By stimulation with brief condenser discharges of a cutaneous sensory nerve in man (digital branch of the median nerve) the authors show that, for a subliminal stimulus, the addition of a further discharge following the 1st one at intervals outlasting 0.1 sec. brought about the perception not only of the shock caused by the 2d discharge, but also of that caused by the 1st one, owing to a process of retroactive facilitation. The existence of such a facilitation is also clearly shown by a shortening of the reaction times to the above stimulus when a second consecutive discharge is delivered at the same intervals as before. The explanation of this fact, which at first seems paradoxical, is to be sought in a delayed elaboration of the response of the esthesio-neurons that condition perception; the cause of that delay is to be found in the necessary intervention of the impulses that follow polysnaptic pathways (mechanism established by Lorente de No in his histological and physiological expts.), the bombardment of those impulses starting some time after the arrival of ineffective direct impulses. At a subliminal intensity the 2d shock delivered between the impulse and the delayed volleys, can make effective the 1st stimulus, thanks to the intervention of its direct impulse, when the polysynaptic impulses started by the first (subliminal) stimulus are delivered; and at a supraliminal intensity the 2d shock accelerates the establishment of an effective level, and thus shortens the latency.