Objective: To characterize tremor frequency oscillatory neurons in the basal ganglia and thalamus in patients with Parkinson’s tremor.

Background: Evidence that the basal ganglia and cerebello-thalamo-cortical circuits are involved in Parkinson’s tremor include: 1) tremor frequency neurons exist in the STN, the GPi and the thalamus (the Vop/Vim); 2) the neurons are coherent with tremor; 3) stimulation of these nuclei suppresses tremor.

Method: Twenty-nine patients with tremor undergoing DBS for the treatment were studied. Microelectrode recordings in the STN, GPi and Vop/Vim with limb EMG were recorded. Single unit analysis was used. Spectral and coherence analyses were applied. Burst analysis was performed. ANOVA and X² test carried out.

Results: Of 99 STN neurons, 48.5% were tremor frequency oscillatory (TFO) neurons and 33% were coherent with tremor. Burst analysis (n=5833) showed Bursting rate (BR): 5.2±3.0Hz; Intraburst rate(IR):119.3±16.3Hz;Burst length(spikes)(BL):7.2±1.5; Burst duration(BD): 69.6±17.2ms; Intraburst Interval(IBI):147.0±26.5ms; Mean cycle period(MCP): 216.7±22.1ms.Of 79 GPi neurons, 50.6% were TFO neurons and 40% were coherent with tremor. Burst analysis (n=3266) showed BR:5.7±1.8Hz; IR:125.2±12.7Hz; BL:15.4±3.0; BD:148.08±40.18ms; IBI: 68.57±12.66ms; MCP:216.8±39.9ms. Of 76 Vop neurons, 59.2% were TFO neurons and 33% coherent with tremor. Burst analysis (n=2829) showed BR:3.6±1.2Hz; IR:124.5±27.9Hz; BL:17.13±4.80; BD:53.8±10.6ms; IBI: 233.0±51.6ms; MCP:287.0±50.3ms.Of 36 Vim neurons, 61.1% were TFO neurons and 63.2% were coherent with tremor. Burst analysis (n=1837) showed BR: 3.8±0.6Hz; IR:126.6±16.3Hz; BL: 6.02±1.67; BD: 55.61±14.52ms; IBI: 211.8±37.4ms; MCP: 267.3±36.0ms. ANOVA showed that there was significant differences of proportion of TFO neurons found in the four nuclei (P<0.05), the highest proportion of TFO neurons was in Vim. Comparisons of burst parameters of four nuclei showed significant differences of BL; BD; IBI and MCP(P<0.05), Bonferroni test indicated that the longest BL and the BD, the shortest IBI and MCP was obtained from GPi as compared to other nuclei (all P<0.05).

Conclusion: The STN, GPi, Vop and Vim play different roles in tremor genesis. The data support the hypothesis that tremor results from the interaction of two circuits: the GPi likely trigger tremor episodes and the cerebello-thalamo-cortical circuit that produces the tremor.

References: 1. Helmich RC, Halett M, Deuschl G, Toni I, Bloem BR. Cerebral cause and consequences of parkinsonian resting tremor: a tale of two circuits? Brain. 2012;135:3206–26.
2. Hallett M. Tremor: pathophysiology Parkinsonism Relat Disord. 2014; 20S1:s118-S122

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MDS Abstracts - https://www.mdsabstracts.org/abstract/characteristics-of-tremor-frequency-oscillatory-neurons-in-the-basal-ganglia-and-thalamus-in-parkinsons-tremor/