The projection from the primary motor and somatic sensory cortex to the basilar pontine nuclei. A detailed electrophysiological and anatomical study in the rat.

The projections from the primary motor and somatic sensory cortex onto the basilar pontine grey were studied in Wistar Rats injecting microvolumes of WGA-HRP solution in sites of the motor and sensory cortex electrophysiologically identified. The main results may be summarized as follows. (a) The projections from both the motor and sensory cortex were found as rostrocaudally oriented columns of terminals in the basilar pontine nuclei. The projection from the motor cortex extended to all over the rostrocaudal extension of the basilar pontine nuclei. To a rostrocaudal shift of the pontine projection field correspond a rostrocaudal displacement in the motor area. The projection from the sensory cortex was mainly restricted to the caudal two thirds of the basilar pontine nuclei, though the hindlimb region of the sensory cortex also showed a discrete representation in the rostral third of the basilar pontine nuclei. (b) The terminal fields of the motor and sensory cortex were segregated except those in the caudal pontine level, which come from the projection of the hindlimb cortical regions. (c) Within the terminal fields of the projections from the motor as well as from the sensory cortex a clearcut topographical arrangement was observed between the projections of cortical areas controlling the head, the forelimb and the hindlimb regions. (d) Within the location of these major subdivisions, the representations of individual body segments were overlapped for a little part ("convergent zones"), whereas the greater part of their projection zones was selective of each cortical field ("private zones"). In conclusion, the present study showed that the projections from the motor and sensory cortex to the basilar pontine nuclei are arranged with a very precise somatotopical organization.