Abstract
The execution of voluntary muscular activity is controlled by the primary motor cortex, together with the cerebellum and basal ganglia. The synchronization of neural activity in the intracortical network is crucial for the regulation of movements. In certain motor diseases, such as dystonia, this synchrony can be altered in any node of the cerebello-cortical network. Questions remain about how the cerebellum influences the motor cortex and interhemispheric communication. This research aims to study the interhemispheric cortical communication between the motor cortices during dystonia, a neurological movement syndrome consisting of sustained or repetitive involuntary muscle contractions. We pharmacologically induced lateralized dystonia to adult male albino mice by administering low doses of kainic acid on the left cerebellar hemisphere. Using electrocorticography and electromyography, we investigated the power spectral densities, cortico-muscular, and interhemispheric coherence between the right and left motor cortices, before and during dystonia, for five consecutive days. Mice displayed lateralized abnormal motor signs, a reduced general locomotor activity, and a high score of dystonia. The results showed a progressive interhemispheric coherence decrease in low-frequency bands (delta, theta, beta) during the first 3 days. The cortico-muscular coherence of the affected side had a significant increase in gamma bands on days 3 and 4. In conclusion, lateralized cerebellar dysfunction during dystonia was associated with a loss of connectivity in the motor cortices, suggesting a possible cortical compensation to the initial disturbances induced by cerebellar left hemisphere kainate activation by blocking the propagation of abnormal oscillations to the healthy hemisphere. However, the cerebellum is part of several overly complex circuits, therefore other mechanisms can still be involved in this phenomenon.
Highlights
The primary motor cortices play the most critical role in generating movement-related neural impulses and controlling the execution of the voluntary muscular activity, together with the cerebellum and basal ganglia [1]
Since the left part of the body was involved in dystonic postures ipsilateral to the left cerebellar cortex where the injection site of kainate was made and the cerebellum sends projections to the contralateral motor cortex, we investigated the coherence between the right motor cortex ECoG and the left part of the neck muscles EMG (Figures 5IA–F)
This research aims to examine the changes in the interhemispheric cortical communication between the primary motor cortices during normal and dystonic state after left hemispheric cerebellar activation with kainate
Summary
The primary motor cortices play the most critical role in generating movement-related neural impulses and controlling the execution of the voluntary muscular activity, together with the cerebellum and basal ganglia [1]. Brain connectivity can be assessed by estimating the extent to which two or more brain regions oscillations are similar [4]. For this reason, one of the most often used methods to evaluate the brain’s synchronous oscillations is coherence, a mathematical parameter. Transcranial magnetic stimulation (TMS) parameters such as the silent period (a pause in the electromyography during voluntary movement after TMS) can indicate the excitability of the corticospinal system [8]. In patients with mirror dystonia (triggered by movements of the healthy arm), the interhemispheric inhibition was reduced [10]. Reduced interhemispheric inhibition was found in patients with writer’s cramp dystonia [11]
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