Objective: To explore the role of abnormal neuronal activity in the basal ganglia and thalamus in the generation of dystonia. Methods: Microelectrode recording was performed in the globus pallidus internus (GPi), ventral thalamic nuclear group ventral oral posterior/ventral intermediate, Vop/Vim) and subthalamic nucleus (STN) in patients with primary dystonia (n = 11) or secondary dystonia (n,= 9) during surgery. Electromyogram (EMG) was simultaneously recorded in selected muscle groups. Single unit analysis and cross-correlations were carried out. Results: Three hundred and sixty-seven neurons were obtained from 29 trajectories (GPi: 13; Vop/Vim: 12; STN: 4), 87% exhibited altered neuronal activity including grouped discharges in GPi (n = 79) and STN (n = 37), long-lasting neuronal activity (n = 70) and rapid neuronal discharge (n = 86) in Vop/Vim. There were neurons in Vop, GPi and STN firing at the same frequency as EMG during dystonia (mean: 0.39 Hz, range 0.12-0.84 Hz). Significant correlations between neuronal activity and EMG at the frequency of dystonia were obtained (GPi: r(2) = 0.7 (n = 31), Vop/Vim: r(2) = 0.64 (n = 18) and STN: r(2) = 0.86 (n = 17)). Conclusions: Consistent with previous findings of abnormalities observed in Vop/VIM and GPi in relation to dystonia, the present data further show that the altered activity in GPi, specifically in dorsal subregions of GPi, Vop/Vim and STN is likely to be directly involved in the production of dystonic movement. Dystonia-related neuronal activity observed in motor thalamus and basal ganglia nuclei of GPi and STN indicates a critical role of their interactions affecting both indirect and direct pathways in the development of either generalized or focal dystonia. Significance: These data support a central role of the basal ganglia in producing dystonic movements. (C) 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.