title: Microelectrode recording findings within the tractography-defined ventral intermediate nucleus.
abstract: OBJECTIVE The ventral intermediate nucleus (VIM) of the thalamus is not visible on structural MRI. Therefore, direct VIM targeting methods for stereotactic tremor surgery are desirable. The authors previously described a direct targeting method for visualizing the VIM and its structural connectivity using deterministic tractography. In this combined electrophysiology and imaging study, the authors investigated the electrophysiology within this tractography-defined VIM (T-VIM). METHODS Thalamic neurons were classified based on their relative location to the T-VIM: dorsal, within, and ventral to the T-VIM. The authors identified the movement-responsive cells (kinesthetic and tremor cells), performed spike analysis (firing rate and burst index), and local field potential analysis (area under the curve for 13-30 Hz). Tremor efficacy in response to microstimulation along the electrode trajectory was also assessed in relation to the T-VIM. RESULTS Seventy-three cells from a total of 9 microelectrode tracks were included for this analysis. Movement-responsive cells (20 kinesthetic cells and 26 tremor cells) were identified throughout the electrode trajectories. The mean firing rate and burst index of cells (n = 27) within the T-VIM are 18.8 ± 9.8 Hz and 4.5 ± 5.4, respectively. Significant local field potential beta power was identified within the T-VIM (area under the curve for 13-30 Hz = 6.6 ± 7.7) with a trend toward higher beta power in the dorsal T-VIM. The most significant reduction in tremor was also observed in the dorsal T-VIM. CONCLUSIONS The electrophysiological findings within the VIM thalamus defined by tractography, or T-VIM, correspond with the known microelectrode recording characteristics of the VIM in patients with tremor.
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto.|Department of Neurosurgery, National Neuroscience Institute, Singapore; and.
authors.forename: Nicolas Kon Kam
authors.initials: NKK
authors.lastname: King
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto.|Center for Neuromodulation, Department of Neurosurgery, The Ohio State University, Columbus, Ohio.
authors.forename: Vibhor
authors.initials: V
authors.lastname: Krishna
authors.affiliation: Department of Physiology, Toronto Western Hospital, University of Toronto, Ontario, Canada.
authors.forename: Diellor
authors.initials: D
authors.lastname: Basha
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto.
authors.forename: Gavin
authors.initials: G
authors.lastname: Elias
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto.
authors.forename: Francesco
authors.initials: F
authors.lastname: Sammartino
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto.|Division of Brain Imaging, Behaviour Systems Neuroscience, Toronto Western Research Institute.
authors.forename: Mojgan
authors.initials: M
authors.lastname: Hodaie
authors.affiliation: Division of Neurosurgery, Department of Surgery, University of Toronto.
authors.forename: Andres M
authors.initials: AM
authors.lastname: Lozano
authors.affiliation: Department of Physiology, Toronto Western Hospital, University of Toronto, Ontario, Canada.
authors.forename: William D
authors.initials: WD
authors.lastname: Hutchison
mesh_terms: D000368:Aged; D015331:Cohort Studies; D056324:Diffusion Tensor Imaging; D004569:Electroencephalography; D020329:Essential Tremor / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D008839:Microelectrodes; D008875:Middle Aged; D010300:Parkinson Disease / Q000000981:diagnostic imaging* / Q000503:physiopathology; D020651:Ventral Thalamic Nuclei / Q000000981:diagnostic imaging* / Q000503:physiopathology*
keywords: CRST = Clinical Rating Scale for Tremor; DBS = deep brain stimulation; DRT = dentatorubrothalamic tract; DTI = diffusion tensor imaging; ISI = interspike interval; LFP = local field potential; MER = microelectrode recording; ML = medial lemniscus; PT = pyramidal tract; ROI = region of interest; T-VIM = tractography-based VIM; VIM = ventral intermediate nucleus; deterministic tractography; functional neurosurgery; microelectrode recording; tractography-based targeting; ventralis intermedius nucleus tractography