Electrophysiological evidence against the hypothesis that corticospinal fibres send collaterals to the lateral reticular nucleus.

Extracellular focal synaptic potentials (FSPs) were recorded in forelimb segments of cats in the region where corticospinal volleys (pyramidal stimulation) gave a maximal FSP. No FSP was recorded in this region on stimulation of the medial part of the lateral reticular nucleus (LRN), provided that ventral spinal pathways through which FSPs can be evoked from the LRN region were transected. It is postulated that the projection from the cerebral cortex to the LRN is not by collaterals from corticospinal neurones but rather by separate corticofugal neurones.