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Corticospinal activation confounds cerebellar effects of posterior fossa stimuli

Lookup NU author(s): Dr Karen Fisher, Dr Mark Baker, Professor Stuart Baker

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Abstract

Objective: To investigate the efficacy of magnetic stimulation over the posterior fossa (PF) as a non-invasive assessment of cerebellar function in man. Methods: We replicated a previously reported conditioning-test paradigm in 11 healthy subjects. Transcranial magnetic stimulation (TMS) at varying intensities was applied to the PF and motor cortex with a 3, 5 or 7 ms interstimulus interval (ISI), chosen randomly for each trial. Surface electromyogram (EMG) activity was recorded from two intrinsic hand muscles and two forearm muscles. Responses were averaged and rectified, and MEP amplitudes were compared to assess whether suppression of the motor output occurred as a result of the PF conditioning pulse. Results: Cortical MEPs were suppressed following conditioning-test ISIs of 5 or 7 ms. No suppression occurred with an ISI of 3 ms. PF stimuli alone also produced EMG responses, suggesting direct activation of the corticospinal tract (CST). Conclusions: CST collaterals are known to contact cortical inhibitory interneurones; antidromic CST activation could therefore contribute to the observed suppression of cortical MEPs. Significance: PF stimulation probably activates multiple pathways; even at low intensities it should not be regarded as a selective assessment of cerebellar function unless stringent controls can confirm the absence of confounding activity in other pathways. (c) 2009 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.


Publication metadata

Author(s): Fisher KM, Lai HM, Baker MR, Baker SN

Publication type: Article

Publication status: Published

Journal: Clinical Neurophysiology

Year: 2009

Volume: 120

Issue: 12

Pages: 2109-2113

Date deposited: 14/06/2010

ISSN (print): 1388-2457

ISSN (electronic): 1872-8952

Publisher: Elsevier Ireland Ltd

URL: http://dx.doi.org/10.1016/j.clinph.2009.08.021

DOI: 10.1016/j.clinph.2009.08.021


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