Patterns of subthalamic synchronized oscillatory neurons are characteristics of motor subtypes of Parkinson's disease

The pathological mechanisms underlying the subtypes of Parkinson's disease (PD) remain unclear. The aim of the study was to explore whether synchronized subthalamic oscillatory neurons are associated with the motor symptoms of PD.

Thirty patients undergoing subthalamic nucleus (STN) deep brain stimulation were included. They were classified tremor dominant (TD, n = 8), indeterminate type (IT, n = 9), and postural instability and gait disorder (PIGD, n = 13) groups. Microelectrode recordings in the STN and the electromyogram (EMG) were recorded. Neuronal background activity was extracted. Spectral and coherence analysis and correlation analysis was used. The locations of the oscillatory neurons were noted.

Of total oscillatory neurons, 95.0% β frequency and 83.3% tremor frequency oscillatory neurons were coherent with their background. Of 76 synchronized β frequency oscillatory neurons, 13.2% were coherent with limb rigidity in PIGD group whereas of 30 synchronized tremor frequency oscillatory neurons, 20% were coherent with tremor in TD group. Tremor frequency and β frequency oscillatory neurons correlated with tremor (r = 0.80 [95% CI 0.23,0.98], P < 0.02) and rigidity/bradykinesia (r = 0.81[95% CI 0.47,0.94], P < 0.0008) sub-scores, respectively. All three subbands of β frequency oscillatory neurons correlated with rigidity/bradykinesia subscores; however, the subband of 13-20 Hz had the strongest correlation (r = 0.64 [95% CI 0.38,0.81], P < 0.0002). The majority of synchronized oscillatory neurons were located in the dorsal STN.

Synchronized tremor frequency and β frequency oscillatory neurons seem to associate with the TD and PIGD subtypes of PD respectively. The low β frequency of 13-20 Hz oscillatory neurons is more implicated for rigidity/bradykinesia. Synchronized oscillatory neurons in the dorsal STN support the idea that the neurons can be used to guide optimal electrode placement.