The effects of repetitive proprioceptive stimulation on corticomotor representation in intact and hemiplegic individuals Gwyn N. Lewis * , Winston D. Byblow Department of Sport and Exercise Science, Human Motor Control Laboratory, University of Auckland, Auckland, New Zealand Accepted 10 November 2003 Abstract Objective: To determine the effects of a passive wrist movement intervention on cortical representation of forearm musculature. Methods: Transcranial magnetic stimulation was used to map cortical representation of a forearm flexor muscle in healthy individuals and in individuals following stroke before and immediately after a 30 min session of passive wrist movement. Results: In the healthy individuals, no changes in map area or map centre of gravity were noted after the intervention; however, map volume increased significantly across all subjects. In the stroke patient group there were no significant changes in any parameters following the intervention. Conclusions: It is speculated that the enlargement in map volume following the passive movement intervention arose through a heightened synaptic efficacy of the corticospinal pathway in response to the increase in afferent information. Short-term proprioceptive stimulation can induce alterations in corticomotor excitability in the target musculature. Significance: These findings provide a potential neural substrate to account for alterations in motor and sensory function in stroke patients in response to long-term passive movement interventions. q 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: Motor cortex; Passive movement; Plasticity; Transcranial magnetic stimulation; Stroke; Afference 1. Introduction The application of passive movement is a common intervention in the recovery phases after stroke, parti- cularly in early stages after insult and in more severely affected individuals. The neural substrate underlying improvements in motor and sensory function in stroke patients in response to induced repetitive proprioceptive stimulation is currently uncertain. Results of recent neural imaging and cortical function studies that have been carried out in neurologically intact individuals may provide some insight into potential mechanisms. A number of studies that have utilized transcranial magnetic stimulation (TMS) have been able to demonstrate the plasticity of cortical motor regions in response to alterations in normal muscle use and activation. Reorganization of cortical motor representation reflecting enhanced neuronal excitability has been noted during and after new skill learning of tasks involving the target muscle (Pascual- Leone et al., 1995; Classen et al., 1998), immediately following a session of repeated activation of target musculature (Cohen et al., 1995, 1996; Liepert et al., 1995), and is also suggested after repeated long-term use of the target muscle, such as in the reading finger of blind subjects who use Braille (Pascual-Leone et al., 1993). These studies suggest that frequent active training can provide a stimulus for cortical reorganization which may serve to assist or facilitate alterations in behavioural requirements. A recent study utilizing positron emission tomography (PET) investigated changes in cerebral blood flow during passive wrist movement in a group of normal subjects before and after 4 weeks of daily passive movement training (Carel et al., 2000). The authors found an increase in primary sensorimotor activity after the 4 week intervention period, suggesting that repeated proprioceptive stimulation can also induce plasticity in sensorimotor representation in healthy individuals. Evidence of direct alterations in the excitability 1388-2457/$30.00 q 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2003.11.014 Clinical Neurophysiology 115 (2004) 765–773 www.elsevier.com/locate/clinph * Corresponding author. Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, IL 60611, USA. Tel.: þ1-312-238-1235; fax: þ 1-312-238-2208. E-mail address: g-lewis3@northwestern.edu (G.N. Lewis).