Corticofugal actions on the lateral cervical nucleus of the cat

The question of possible corticofugal actions on the lateral cervical nucleus (LCN) of the cat was reinvestigated. Recordings were made from single relay cells, identified histologically as lying in the LCN which was deafferented by spinal cord lesions to avoid interference from corticospinal-cervical pathways. Intracortical stimulation of the contralateral sensorimotor cortex inhibited all 53 cells studied, but in addition excited only 25% of them (mean latency 5 ms). Cortical stimulation also inhibited mass transmission through the LCN. Care was taken to avoid inhibition due to stimulating high-threshold receptors in the head. Exploration with the stimulating electrode of large parts of the cerebral cortex allowed lowest threshold (45 to 90 μA; 10 ms train of cortical shocks of 1 ms duration at 500 Hz) zones for inhibition of the LCN to be located, but no low-threshold zones for excitation could be found. (Indirect current spread with such stimulation of the cortex was shown to be about 1.5 mm.) Histological reconstruction of the stimulating tracks showed that the low-threshold zone was cylindrical, rostrally, lying in the grey matter of that part of the cytoarchitectural area 3a which represents the face. Caudally, the low-threshold zone was in white matter where the corticofugal pathway would be expected to course. Such a nonsomatotopically organized inhibitory pathway is unusual in sensory systems and suggests that the LCN may be involved in certain tasks requiring face-limb coordination.