DIFFERENTIAL CONTRIBUTION OF CORTICOSPINAL AND CORTICORUBRAL NEURONS IN REACHING BEHAVIOR

The specific roles of distinct subtypes of pyramidal tract neurons (PTNs) in movement within the sensorimotor cortex remain largely unknown. In this study, we examined the functional roles of two classes of PTNs: corticospinal tract neurons (CS), which project to the spinal cord, and corticorubral tract neurons (CR), which project to the red nucleus. Our aim is to characterize their individual electrophysiological properties, as well as the involvement of both neural pathways in voluntary reaching movements. Furthermore, we seek to determine whether they exhibit differential roles in kinematics and biomechanics during the preparatory and execution phases, in addition to specific forelimb movements.
To achieve this, we conducted optotagging experiments targeting sensorimotor CS or CR neurons in the primary motor cortex in anesthetized rats. We analyzed and described the differential electrophysiological properties (spontaneous and evoked activity, firing rate, and latency) of all the photoidentified units. Additionally, we recorded CS and CR neurons in the primary motor cortex during a behavioral task of reaching movement and aligned the neuronal activity with the kinematics of the right forelimb of the rat obtained with DeepLabCut software. We find that CS neurons play a greater role in regulating the velocity of the reaching movement and throughout its entire execution. In contrast, CR neurons are more involved in the movement preparation and reaction time. These results indicates a differential functional role of distinct classes of pyramidal tract neurons in sensorimotor control.