Tremor cells in the human thalamus: differences among neurological disorders

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Object. Thalamic neurons firing at frequencies synchronous with tremor are thought to play a critical role in the generation and maintenance of tremor. The authors studied the incidence and locations of neurons with tremor-related activity (TRA) in the thalamus of patients with varied pathological conditions—including Parkinson disease (PD), essential tremor (ET), multiple sclerosis (MS), and cerebellar disorders—to determine whether known differences in the effectiveness of thalamic stereotactic procedures for these tremors could be correlated to differences in the incidence or locations of TRA cells.

Methods. Seventy-five operations were performed in 61 patients during which 686 TRA cells were recorded from 440 microelectrode trajectories in the thalamus. The locations of the TRA cells in relation to electrophysiologically defined thalamic nuclei and the commissural coordinates were compared among patient groups.

The authors found that TRA cells are present in patients with each of these disorders and that these cells populate several nuclei in the ventral lateral tier of the thalamus. There were no large differences in the locations of TRA cells among the different diagnostic classes, although there was a difference in the incidence of TRA cells in patients with PD, who had greater than 3.8 times more cells per thalamic trajectory than patients with ET and approximately five times more cells than patients with MS or cerebellar disorders.

Conclusions. There was an increased incidence of TRA in the thalamus of patients with PD. The location of thalamic TRA cells in patients with basal ganglia and other tremor disorders was similar.

Article Information

Address reprint requests to: Andres M. Lozano, M.D., Ph.D., Division of Neurosurgery, Toronto Western Hospital, 4–447 West Wing, 399 Bathurst Street, Toronto, Ontario, Canada M5T 2S8. email: lozano@uhnres.utoronto.ca.

© AANS, except where prohibited by US copyright law.

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Figures

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    Correlation between thalamic neuronal activity and tremor. Upper: Trace obtained from a single thalamic unit in a patient with ET, correlating to a trace of arm tremor recorded using an accelerometer (Acc). Lower: Traces showing the correlation between thalamic tremor cell activity in a patient with PD and contralateral arm on EMG recordings.

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    Position of tremor cells relative to the PC and the intercommissural line. Note that TRA cells are located in most of the ventrolateral thalamus, but are primarily centered in the Vim region. A: Patients with PD (431 cells). B: Patients with ET (114 cells). C: Patients with MS (97 cells). D: Patients with cerebellar or posttraumatic tremor (44 cells). Scale: ticks are 2 mm apart.

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    Average location of TRA cells by diagnostic group relative to the PC and the intercommissural line. Parkinson disease is represented by the open circle, ET by the closed square, MS by the closed triangle, and cerebellar and posttraumatic tremor by the open triangle. Scale: ticks are 2 mm apart.

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    Average location of TRA cells by diagnostic group relative to the physiologically defined thalamic borders. Parkinson disease is represented by the open circle, ET by the closed square, MS by the closed triangle, and cerebellar and posttraumatic tremor by the open triangle. Scale: ticks are 2 mm apart.

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