Objective: To explore the role of neuronal activity in the globus pallidus internus (GPi) in the generation of tic movements.
Methods: We studied eight Tourette syndrome patients with medically intractable tics who underwent a unilateral pallidotomy for severe tics. They ranged in age from 17-24 years; disease duration was 7-19 years. Microelectrode recording was performed in the GPi. The electromyogram (EMG) was simultaneously recorded in muscle groups appropriate for the patient's tics. The relationship between neuronal firing pattern and the EMG was studied.
Results: Two hundred and thirty-two neurons were recorded during tics from 8 trajectories. Of these neurons, in addition to decreased neuronal firing rate and irregular firing pattern, 105 (45%) were tic-related showing either a burst of activity or a pause in ongoing tonic activity. They could be synchronous (n=75), earlier than EMG onset (n=27), or following EMG onset (n=3). The GPi neuronal bursts preceded EMG onset with decreased (n=6) or increased activity (n=21). The initial change in neural activity occurred about 50 ms to 2s before the EMG onset.
Conclusions: Although the data are descriptive and preliminary, the tic-related neuronal activity observed in GPi appears to indicate that the basal ganglia motor circuit is involved in tic movements. The early neuronal activity seen in GPi may reflect premonitory sensations that precede a tic.
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