SEGREGATED PARALLEL INPUTS TO THE BRACHIAL SPINAL-CORD FROM THE CINGULATE MOTOR CORTEX IN THE MONKEY

The corticospinal projection from the cingulate motor cortex to the lo wer cervical enlargement (C-5-T-1) was investigated in four rhesus mon keys. Each received an injection of biotinylated dextran amine involvi ng the arm representation of M3 (area 24c) or M4 (area 23c). In M3 cas es, contralateral terminal label occurred in the lateral part of lamin ae V and VI of the intermediate zone including the reticulated margina l border. Lighter labeling was found in laminae IV, VII and the dorsol ateral part of the anterior horn (lamina IX). In marked contrast, M4 c ases demonstrated contralateral terminal labeling in the medial part o f the dorsal and intermediate zones (laminae III, IV, V and VI). Light er labeling involved the medial part of laminae VII, X and the dorsola teral anterior horn (lamina IX). Our experiments demonstrate that the corticospinal projection from the arm representations of M3 and M4 inn ervate distinct and separate parts of the spinal gray. Along with the noted differences in the cortical inputs to M3 and M4, these data sugg est that the two cingulospinal systems may mediate independent and spe cialized forms of information effecting upper limb movement.