Lateralization of motor imagery following stroke Cathy M. Stinear a, * , Melanie K. Fleming a , P. Alan Barber b , Winston D. Byblow a a Department of Sport & Exercise Science, Movement Neuroscience Laboratory, University of Auckland, Private Bag 92019, Auckland, New Zealand b Department of Neurology, Auckland City Hospital, Auckland, New Zealand Accepted 10 May 2007 Abstract Objective: Motor imagery may activate the primary motor cortex (M1) and promote functional recovery following stroke. We investi- gated whether the hemisphere affected by stroke affects performance and M1 activity during motor imagery. Methods: Twelve stroke patients (6 left, 6 right hemisphere) and eight healthy age-matched adults participated. Experiment 1 assessed the speed and ease of actual and imagined motor performance. Experiment 2 measured corticomotor excitability during imagined move- ment of each hand separately, and both hands together, using transcranial magnetic stimulation. Results: For control participants, imagined movements were performed more slowly than actual movements, and right-hand MEPs were facilitated when they imagined moving their right hand or both hands together. Patients reported being able to imagine movements with either hand, despite no measurable facilitation of MEPs in the stroke-affected hand. In left hemisphere patients, MEPs were facilitated in the left hand during imagery of the right hand and both hands together. In right hemisphere patients, motor imagery did not facilitate MEPs in either hand. Conclusions: Motor imagery does not appear to facilitate the ipsilesional M1 following stroke. Significance: Motor imagery may play a role in rehabilitating movement planning, but its role in directly facilitating corticomotor output appears limited. Ó 2007 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: Cortex; Motor activity; Transcranial magnetic stimulation; Rehabilitation 1. Introduction Motor imagery and mental practice may have therapeu- tic application for people recovering from stroke at a time when weakness and fatigability limit physical practice, in the same way that motor imagery is used in sport to improve performance (Sharma et al., 2006). Motor imagery can be defined as ‘‘a dynamic state during which the repre- sentation of a given motor act is internally rehearsed within working memory without any overt motor output’’ (Decety and Grezes, 1999). In healthy adults, motor imagery engages motor cortical areas, including primary motor (M1), premotor, supplementary motor, cingulate and pari- etal cortex (Porro et al., 1996; Deiber et al., 1998; Gerardin et al., 2000; Ehrsson et al., 2003; Hanakawa et al., 2003; Jackson et al., 2003). Transcranial magnetic stimulation (TMS) has been used to show that excitability of M1 is increased during kinesthetic motor imagery, and changes with the same temporal and spatial characteristics as dur- ing actual movement (Rossi et al., 1998; Fadiga et al., 1999; Hashimoto and Rothwell, 1999; Yahagi and Kasai, 1999; Facchini et al., 2002; Stinear and Byblow, 2003). Little is known about how stroke affects cortical func- tion during motor imagery. Two studies have examined the behavioral effects of the side of stroke on imagined hand movements: left hemisphere stroke results in bilateral slowing of imagined hand movements; while the results after right hemisphere stroke are less clear with slowed imagined movement of either both hands (Malouin et al., 2004) or the left hand only (Sabate et al., 2004). More 1388-2457/$32.00 Ó 2007 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2007.05.008 * Corresponding author. Tel.: +64 9 3737 599x83766; fax: +64 9 3737 043. E-mail address: c.stinear@auckland.ac.nz (C.M. Stinear). www.elsevier.com/locate/clinph Clinical Neurophysiology 118 (2007) 1794–1801