The Central Medial Thalamic Nucleus Facilitates Bilateral Movement Execution in Rats.

Intralaminar thalamic nuclei, including the central medial nucleus (CMT), have been classically implicated in the control of attentional functional states such as sleep-wake transitions. In rodents, the CMT innervates large cortical and subcortical areas bilaterally, including sensorimotor regions of the cortex and striatum, but its contribution to motor function, which regularly develops in faster temporal scales than attentional states, is still far from being completely understood. Here, by using a novel behavioral protocol to evaluate bilateral coordination in rats, combined with electrophysiological recordings and optogenetic manipulations, we studied the contribution of the CMT to motor control and coordination. We found that optogenetic stimulation of the central region of the CMT produced bilateral recruitment of neural activity in the sensorimotor cortex and striatum. The same type of stimulations produced a significant increase in bilateral movement coordination of the forelimbs accompanied by a decrease in movement trajectory variability. Optogenetic inactivation of the CMT did not affect motor execution but significantly increased execution times, suggesting less interest in the task. Altogether, our results indicate that brief CMT activations create windows of synchronized bilateral cortico-striatal activity, suitable to facilitate motor coordination in temporal scales relevant for motor execution.

Cortico-striatal circuits for bilaterally coordinated movements.

Movement initiation and control require the orchestrated activity of sensorimotor cortical and subcortical regions. However, the exact contribution of specific pathways and interactions to the final behavioral outcome are still under debate. Here, by combining structural lesions, pathway-specific optogenetic manipulations and freely moving electrophysiological recordings in rats, we studied cortico-striatal interactions in the context of forelimb bilaterally coordinated movements. We provide evidence indicating that bilateral actions are initiated by motor cortical regions where intratelencephalic bilateral cortico-striatal (bcs-IT) projections recruit the sensorimotor striatum to provide stability and duration to already commanded bilateral movements. Furthermore, striatal spiking activity was correlated with movement duration and kinematic parameters of the execution. bcs-IT stimulation affected only the representation of movement duration but spared that of kinematics. Our findings confirm the modular organization of information processing in the striatum and its involvement in moment-to-moment movement control but not initiation or selection.

Altered Sensory Representations in Parkinsonian Cortical and Basal Ganglia Networks.

In parkinsonian conditions, network dynamics in the cortical and basal ganglia circuits present abnormal oscillations and periods of high synchrony, affecting the functionality of multiple striatal regions including the sensorimotor striatum. However, it is still unclear how these altered dynamics impact on sensory processing, a key feature for motor control that is severely impaired in parkinsonian patients. A major confound is that pathological dynamics in sensorimotor networks may elicit unspecific motor responses that may alter sensory representations through sensory feedback, making it difficult to disentangle motor and sensory components. To address this issue, we studied sensory processing using an anesthetized model with robust sensory representations throughout cortical and basal ganglia sensory regions and limited motor confounds in control and hemiparkinsonian rats. A general screening of sensory-evoked activity in large populations of neurons recorded in the primary sensory cortex (S1), dorsolateral striatum (DLS) and substantia nigra pars reticulata (SNr) revealed increased excitability and altered sensory representations in the three regions. Further analysis revealed uncoordinated population dynamics between DLS and S1/SNr. Finally, DLS lesions in hemiparkinsonian animals partially recovered population dynamics and execution in the rotarod.