Inhibition of the dorsal column nuclei

Recordings of electrical changes were made in the dorsal column nuclei in decerebrated cats, in some of which the pericruciate, coronal, and anterior ectosylvian gyri, or parts thereof, were chronically ablated. Single weak test volleys from skin and peripheral nerve or dorsal columns of cord evoked responses slightly above threshold. These were conditioned from either contralateral bulbar pyramid or reticular formation by repetitive volleys. Inhibition of the nuclei of the dorsal columns is obtainable from the contralateral and to a slight extent from the ipsilateral pyramid and from the reticular formation both crossed and uncrossed. The cortical area which yields pyramidal inhibition comprises the pericruciate, coronal, and anterior ectosylvian gyri. The pyramid inhibition is not mediated via the reticular formation above the level of the dorsal column nuclei. It requires at least five volleys and increases in effectiveness up to twenty volleys. It is relatively weak and is easily overcome by large test volleys. It may last for over 200 msec and to a slight degree for several seconds. It is virtually eliminated by small doses of sodium pentobarbital which may reveal a previously hidden facilitation. We regard it as direct inhibition and not as a result of refractoriness.