Objective: To explore whether subthalamic tremor-related oscillatory neurons is involved in the generation of Parkinson’s tremor.

Background: Both the basal ganglia and cerebello-thalamo-cortical circuits appear to be involved in Parkinson’s tremor. However, exactly how tremor is generated remains a critical question. The basal ganglia certainly seem important because (1) tremor frequency oscillatory neurons exist in the subthalamic nucleus (the STN), (2) these neurons are significantly coherent with limb tremor, and (3) stimulation of the STN (DBS) suppresses tremor suggesting that the STN has an important pathophysiological role in producing tremor. Furthermore, recent findings suggest that the STN receives direct anatomic projections from cortex and sends disynaptic anatomic projections to the cerebellar. Whether the STN is a part of a basal ganglia trigger or whether the STN is involved in tremor genesis itself remains unclear.

Method: Ten PD patients with bradykinesia, rigidity, and tremor undergoing surgery for DBS were studied. Microelectrode recordings in the STN and electromyographic (EMG) activity in the limbs were recorded and the mean spontaneous firing rates (MSFRs) were calculated. Spectral analysis was used to evaluate neuronal oscillatory patterns. Coherence analysis was applied to explore the relationship between oscillatory neuronal activity and limb EMG.

Results: Of 93 STN neurons, 48.38% oscillated at the tremor frequency (4.48 ± 0.49 Hz); 22.58% oscillated at β frequency (16.05±7.52 Hz), and the rest (29.03%) did not oscillate. The MSFR of all neurons was 40.64 ± 5.86 spikes/s. Among 45 neurons oscillating at tremor frequency, 40% were coherent with the tremor. In 9 neurons, during the recording the pattern changed from tremor frequency to β frequency associated with limb tremor or vice versa. In particular, it appeared that the change in those STN tremor related oscillatory neurons preceded changes in limb tremor.

Conclusion: Subthalamic tremor frequency oscillatory neurons coherent with tremor further confirm that the STN is involved in pathophysiology of tremor. That some subthalamic tremor- related oscillatory neurons change activity prior to changes in limb tremor, the STN seems to play an important role in tremor initiation.

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/subthalamic-tremor-related-oscillatory-neurons-play-a-role-in-the-generation-of-parkinsons-tremor/