Area-specific processing of cerebellar-thalamo-cortical information in primates

The cerebellar-thalamo-cortical (CTC) system plays a major role in controlling timing and coordination of voluntary movements. However, the functional impact of this system on motor cortical sites has not been documented in a systematic manner. We addressed this question by implanting a chronic stimulating electrode in the superior cerebellar peduncle (SCP) and recording evoked multiunit activity (MUA) and the local field potential (LFP) in the primary motor cortex (), the premotor cortex () and the somatosensory cortex (). The area-dependent response properties were estimated using the MUA response shape (quantified by decomposing into principal components) and the time-dependent frequency content of the evoked LFP. Each of these signals alone enabled good classification between the somatosensory and motor sites. Good classification between the primary motor and premotor areas could only be achieved when combining features from both signal types. Topographical single-site representation of the predicted class showed good recovery of functional organization. Finally, the probability for misclassification had a broad topographical organization. Despite the area-specific response features to SCP stimulation, there was considerable site-to-site variation in responses, specifically within the motor cortical areas. This indicates a substantial SCP impact on both the primary motor and premotor cortex. Given the documented involvement of these cortical areas in preparation and execution of movement, this result may suggest a CTC contribution to both motor execution and motor preparation. The stimulation responses in the somatosensory cortex were sparser and weaker. However, a functional role of the CTC system in somatosensory computation must be taken into consideration

Cerebellar Shaping of Motor Cortical Firing Is Correlated with Timing of Motor Actions

Summary: In higher mammals, motor timing is considered to be dictated by cerebellar control of motor cortical activity, relayed through the cerebellar-thalamo-cortical (CTC) system. Nonetheless, the way cerebellar information is integrated with motor cortical commands and affects their temporal properties remains unclear. To address this issue, we activated the CTC system in primates and found that it efficiently recruits motor cortical cells; however, the cortical response was dominated by prolonged inhibition that imposed a directional activation across the motor cortex. During task performance, cortical cells that integrated CTC information fired synchronous bursts at movement onset. These cells expressed a stronger correlation with reaction time than non-CTC cells. Thus, the excitation-inhibition interplay triggered by the CTC system facilitates transient recruitment of a cortical subnetwork at movement onset. The CTC system may shape neural firing to produce the required profile to initiate movements and thus plays a pivotal role in timing motor actions. : Nashef et al. identified a motor cortical subnetwork recruited by cerebellar volley that was transiently synchronized at movement onset. Cerebellar control of cortical firing was dominated by inhibition that shaped task-related firing of neurons and may dictate motor timing. Keywords: motor control, primates, cerebellar-thalamo-cortical, synchrony, noise correlation, reaction tim