Subthalamic nucleus phase-amplitude coupling correlates with motor impairment in Parkinson's disease.
van Wijk BC., Beudel M., Jha A., Oswal A., Foltynie T., Hariz MI., Limousin P., Zrinzo L., Aziz TZ., Green AL., Brown P., Litvak V.
OBJECTIVE: High-amplitude beta band oscillations within the subthalamic nucleus are frequently associated with Parkinson's disease but it is unclear how they might lead to motor impairments. Here we investigate a likely pathological coupling between the phase of beta band oscillations and the amplitude of high-frequency oscillations around 300 Hz. METHODS: We analysed an extensive data set comprising resting-state recordings obtained from deep brain stimulation electrodes in 33 patients before and/or after taking dopaminergic medication. We correlated mean values of spectral power and phase-amplitude coupling with severity of hemibody bradykinesia/rigidity. In addition, we used simultaneously recorded magnetoencephalography to look at functional interactions between the subthalamic nucleus and ipsilateral motor cortex. RESULTS: Beta band power and phase-amplitude coupling within the subthalamic nucleus correlated positively with severity of motor impairment. This effect was more pronounced within the low-beta range, whilst coherence between subthalamic nucleus and motor cortex was dominant in the high-beta range. CONCLUSIONS: We speculate that the beta band might impede pro-kinetic high-frequency activity patterns when phase-amplitude coupling is prominent. Furthermore, results provide evidence for a functional subdivision of the beta band into low and high frequencies. SIGNIFICANCE: Our findings contribute to the interpretation of oscillatory activity within the cortico-basal ganglia circuit.