The aim of this study was to quantify the characteristics of oscillatory neurons in the globus pallidus internus (GPi) in patients with Parkinson’s disease (PD).

The pathophysiology underlying parkinsonian motor deficits remain unclear.  Tremor frequency neurons in the basal ganglia have been predicted to be involved in tremor genesis.

Six patients with PD (4 males, 2 females; age: 58.67±6.15 years) who underwent electrode implantation for GPi deep brain stimulation or pallidotomy were studied. Microelectrode recordings of the GPi neuronal activity were obtained during surgery for PD. EMG on the contralateral limbs was performed. The interspike intervals were assessed. Spectral analysis was used to evaluate neuronal oscillatory activity. Coherence was calculated. Mean firing rates and proportions of patterns of GPi oscillatory neurons were identified. Coherence analysis was used to study relationship between oscillatory activity and limb symptoms.  

Of 55 GPi oscillatory neurons identified, 58.2% (n=32) were tremor frequency (at mean frequency of 4.67±0.71Hz) oscillatory neurons, 16.4% (n=9) were ß frequency oscillatory neurons (at mean frequency of 15.84 ±8.33 Hz) and 25.4% (n=14) were non-oscillatory neurons. Of these tremor frequency oscillatory neurons, 50% neurons were significantly coherent with limb tremor (coherence magnitude range of 0.52–0.85, mean: 0.72± 0.14). The mean firing rate of all neurons was 81.46±7.44 Hz. 

Consistent with previous the findings, there were three types of oscillatory neurons: tremor frequency, β frequency and non-oscillatory neurons in the GPi. The presence of high proportion of tremor related oscillatory neurons in the GPi and their strong coherence, supports a role of the globus pallidus in the production of rest tremor in PD patients.