The cortical projection to the nucleus reticularis tegmenti pontis in the rhesus monkey

SummaryThe projection from the cerebral cortex to the nucleus reticularis tegmenti pontis (NRT) has been studied in the rhesus monkey with silver impregnation methods. The majority of cortical afferents to NRT arise in the precentral motor cortex (area 4), while more modest contributions come from the premotor region (area 6), the somatosensory cortex (areas 3, 1, and 2) and area 5. Very few, if any, degenerating fibres were observed in the NRT after lesions of other parts of the cortex. The cortical afferents terminate throughout NRT except in its dorsomedial part. There is a topographical arrangement so that fibres from area 6 terminate most medially in the NRT, fibres from area 5 most laterally (in the processus tegmentosus lateralis), while fibres from the motor cortex end in between and cover the largest terminal field. In addition, the projection from the motor cortex is somatotopically organized with the leg represented ventrally and the arm dorsally in the NRT. There is, however, ample overlap between the terminal regions of fibres from the various cortical areas. The results are discussed in relation to the termination of other afferent contingents to the NRT, and it is concluded that even if there is a high degree of convergence, various parts of the NRT appear not to receive identical sets of afferent inputs.

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