Cortical actions on hypoglossal motoneurones in cats: a proposed role for a common internuncial cell.

1. Intracellular records were made of the synaptic potentials produced in hypoglossal motoneurones when electrical stimuli were applied to the cat's motor cortex.2. The depolarizing synaptic responses reached their maxima in steps similar to those produced in the same motoneurones by suprathreshold stimulation of the lingual nerve.3. Interneurones in or near the spinal trigeminal nucleus were caused to discharge by cortical shocks adequate to produce synaptic potentials in hypoglossal motoneurones. The latencies and patterns of repetitive responses in these interneurones were consistent with their possible role as internuncial cells in the motor pathway from cerebral cortex to hypoglossal motoneurones.4. Individual interneurones in or near the spinal trigeminal nucleus could be caused to discharge both by stimulation of the lingual nerve and by stimulation of the motor cortex. This convergence suggests a common function for the internuncial cell in reflexly and cortically induced excitation of hypoglossal motoneurones and would allow the internuncial cell to be a site for integration of spatially separated excitatory influences.