Chronic but not acute dopaminergic transmission interruption promotes a progressive increase in cortical beta frequency synchronization: relationships to vigilance state and akinesia.

Dopaminergic (DA) denervation results in the appearance of an excessive cortical beta frequency synchronization in parkinsonian patients and animal models of the disease. The present study analyzed electrocorticogram signals in awake rats to further characterize this excessive synchronization in terms of time course, relation to motor activity and state of vigilance. Using substantia nigra pars compacta lesions and both acute and chronic pharmacological interruptions of DA transmission, the present data demonstrated that the appearance of excessive beta synchronization requires a prolonged interruption in DA transmission and builds up progressively. This synchronization was vigilance-state dependent and observed solely during awake-like activity. Furthermore, these data demonstrated for the first time that the appearance of akinesia preceded the excessive cortical beta synchronization. In addition, this synchronization was stronger in the motor than in the somato-sensory cortex and in unilaterally compared with bilaterally lesioned animals. Finally, excessive beta synchronization was accompanied by an increased coherence between motor and somato-sensory cortical activities. These data suggest that excessive beta synchronization is associated with plastic processes whose time course is delayed with respect to the akinesia. Moreover, the expression of this phenomenon, which likely reflects functional changes in the cortico-basal ganglia circuits, requires a specific brain state.