High-frequency synchronization of neuronal activity in the subthalamic nucleus of parkinsonian patients with limb tremor

It has been hypothesized that in Parkinson's disease (PD) there is increase d synchronization of neuronal firing in the basal ganglia. This study exami nes the discharge activity of 121 pairs of subthalamic nucleus (STN) neuron s in nine PD patients undergoing functional stereotactic mapping. Four pati ents had a previous pallidotomy. A double microelectrode setup was used to simultaneously record from two neurons separated by distances as small as 2 50 mu m. In the six patients who had limb tremor during the recording sessi on (n = 76 pairs), the discharge pattern of 12 pairs of tremor cells (TCs) was found to be coherent at the frequency of the limb tremor. Both in-phase and out-of-phase relationships were observed between TCs. Interestingly, i n these six patients, 63/129 single neurons displayed 15-30 Hz oscillations , whereas 36/76 pairs were coherent in this frequency range. Although the o scillatory frequencies were variable between patients, they were highly clu stered within a patient. The phase difference between these pairs was found to be close to 0. High-frequency synchronization was observed during perio ds of limb tremor as well as during intermittent periods with no apparent l imb tremor. In contrast, in the three patients without limb tremor during t he recording session, only 1/84 neurons had high-frequency oscillatory acti vity, and no TCs or synchronous high-frequency oscillatory activity was obs erved (n = 45 pairs). These findings demonstrate that in PD patients with l imb tremor, many STN neurons display high-frequency oscillations with a hig h degree of in-phase synchrony. The results suggest that high-frequency syn chronized oscillatory activity may be associated with the pathology that gi ves rise to tremor in PD patients.