Organization of somatic motor inputs from the frontal lobe to the pedunculopontine tegmental nucleus in the macaque monkey

To reveal the somatotopy of the pedunculopontine tegmental nucleus that fun ctions as a brainstem motor center, we examined the distribution patterns o f corticotegmental inputs from the somatic motor areas of the frontal lobe in the macaque monkey. Based on the somatotopical map prepared by intracort ical microstimulation, injections of the anterograde tracers, biotinylated dextran amine and wheat germ agglutinin-conjugated horseradish peroxidase, were made into the following motor-related areas: the primary motor cortex, the supplementary and presupplementary motor areas, the dorsal and ventral divisions of the premotor cortex, and the frontal eye field. Data obtained from the present experiments were as follows: (i) Corticotegmental inputs from orofacial, forelimb, and hindlimb representations of the primary motor cortex tended to be arranged orderly from medial to lateral in the peduncu lopontine tegmental nucleus. However, the distribution areas of these input s considerably overlapped; (ii) The major input zones from distal represent ations of the: forelimb and hindlimb regions of the primary motor cortex we re located medial to those from their proximal representations, although th ere was a substantial overlap between the distribution areas of distal vers us proximal limb inputs; (iii) The main terminal zones from the forelimb re gions of the primary motor cortex, the supplementary and presupplementary m otor areas, and the dorsal and ventral divisions of the premotor cortex app eared to overlap largely in the mediolaterally middle aspect of the peduncu lopontine tegmental nucleus; and (iv) Corticotegmental input from the front al eye field was scattered over the pedunculopontine tegmental nucleus. Thus, the present results indicate that the pedunculopontine tegmental nucl eus is likely to receive partly separate but essentially convergent cortica l inputs not only from multiple motor-related areas representing the same b ody part, hut also from multiple regions representing diverse body parts. T his suggests that somatotopical representations are intermingled rather tha n segregated in the pedunculopontine tegmental nucleus. (C) 2000 IBRO. Publ ished by Elsevier Science Ltd. All rights reserved.