Activation of descending control of the spinocervical tract by impulses ascending the dorsal columns and relaying through the dorsal column nuclei.

1. Micro-electrode recordings were made from axons of the spinocervical tract in unanaesthetized decerebrate cats.2. Orthodromic activation of the dorsal columns and dorsal column nuclei was used to condition responses evoked in spinocervical tract neurones from cutaneous nerves. Such conditioning produced inhibition of transmission through the tract. The inhibition had a time course of 200 msec or more with maximal action at 30-70 msec and was most effective against polysynaptic responses.3. After removal of the cerebellum or section of the cerebellar peduncles the degree of inhibition was reduced but inhibition could still be evoked by activation of the dorsal columns and dorsal column nuclei.4. Transection of the brain stem just rostral to the dorsal column nuclei removed the inhibitory effects although segmental inhibition was not affected.5. It is concluded that impulses ascending the dorsal columns and relaying through the dorsal column nuclei can lead to activation of descending control of the spinocervical tract. Parts of the pathways involved include the cerebellum and the brain stem. It is unlikely that the cells in the dorsal column nuclei which have descending axons are concerned with the control of transmission through the spinocervical tract.