It is by no means clear however that this contralesional activity is the same phenomenon as that which generates pathological inhibition of the recovering hemisphere, or that it is necessarily maladaptive. There is evidence that at least some regions on the non-stroke side may support movement of the paretic side, such as the contralesional dorsal premotor cortex which displays increased functional connectivity to the primary motor cortex of the stroke in more affected patients and appears to support hand movement.11,12Furthermore a recent study suggested that reducing intact hemisphere excitability may in fact be detrimental to upper limb function in more impaired patients.3
As the role of contralesional brain regions in movement appears to differ depending upon factors such as clinical severity, extent of corticospinal tract disruption and possibly stroke location it would seem that reducing excitability on that side equally in all stroke patients may represent rather a blunt therapeutic approach. This is especially true of tDCS, whose effects incorporate most of the stimulated hemisphere. However, positive studies may be found in the literature for both repetitive TMS and tDCS when applied to either side of the brain (sometimes both), and although a comprehensive review of the outcomes is beyond the scope of this article the most promising approach appears to be inhibition of the non-stroke hemisphere by tDCS.13 Non-invasive brain stimulation has not as yet entered routine clinical practice however, and there are a number of reasons why this may be, such as the large number of stimulation protocols available and uncertainty regarding the optimal time to apply stimulation. However, for the reasons discussed above it is important to consider the heterogeneity of the clinical syndrome when designing further trials. Opinions differ as to whether progress will be made using a ‘one size fits all’ design, the hope being that larger sample sizes will take care of heterogeneity, or alternatively whether targeting stimulation according to clinical and physiological factors would have a greater chance of success. This is likely to be worth getting right, as a large negative study would present an obstacle to further investigation in this field. It is likely to be the case that applying brain stimulation to the right patients could significantly enhance the outcome of post-stroke rehabilitation, with a clinically meaningful reduction in resulting impairment and disability.
- Reis J, Swayne OB, Vandermeeren Y, Camus M, Dimyan MA, Harris-Love M, Perez MA, Ragert P, Rothwell JC, Cohen LG. Contribution of transcranial magnetic stimulation to the understanding of cortical mechanisms involved in motor control. J Physiol 2008; 586(2):325-51.
- Stinear CM, Barber PA, Smale PR, Coxon JP, Fleming MK, Byblow WD. Functional Potential in chronic stroke patients depends on corticospinal tract integrity. Brain 2007;130:170-180.
- Bradnam LV, Stinear CM, Barber PA, Byblow WD. Contralesional hemisphere control of the proximal paretic upper limb following stroke. Cereb Cortex. 2012 Nov;22(11):2662-71.
- Traversa R, Cicinelli P, Pasqualetti P, Filippi M, Rossini PM. Follow-up of interhemispheric differences of motor evoked potentials from the ‘affected’ and ‘unaffected’ hemispheres in human stroke. Brain Research 1998; 803:1-8.
- Manganotti P, Patuzzo S, Cortese F, Palermo A, Smania N, Fiaschi A. Motor disinhibition in affected and unaffected hemisphere in the early period of recovery after stroke. Clin Neurophysiol 2002; 113:936-943.
- Swayne OB, Rothwell JC, Ward NS, Greenwood RJ. Stages of Motor Output Reorganization after Hemispheric Stroke Suggested by Longitudinal Studies of Cortical Physiology. Cereb Cortex 2008; 18:1909- 1922.
- McDonnell MN, Stinear CM. TMS measures of motor cortex function after stroke: A meta-analysis. Brain Stimul. 2017 Jul – Aug;10(4):721-734.
- Murase N, Duque J, Mazzocchio R, Cohen LG. Influence of interhemispheric interactions on motor function in chronic stroke. Ann Neurol 2004; 55:400-409.
- Blicher JU, Near J, Næss-Schmidt E, Stagg CJ, Johansen-Berg H, Nielsen JF, Østergaard L, Ho YC. GABA levels are decreased after stroke and GABA changes during rehabilitation correlate with motor improvement. Neurorehabil Neural Repair 2015 Mar-Apr;29(3):278-86.
- Delvaux V, Alagona G, Gerard P, De Pasqua V, Pennisi G, de Noordhout AM. Post-stroke reorganization of hand motor area: a 1-year prospective follow-up with focal transcranial magnetic stimulation. Clin Neurophysiol 2003; 114:1217-1225
- Bestmann S, Swayne O, Blankenburg F, Ruff CC, Teo J, Weiskopf N, Driver J, Rothwell JC, Ward NS. The role of contralesional dorsal premotor cortex after stroke as studied with concurrent TMS-fMRI. J Neurosci 2010; 30(36):11926-37.
- Johansen-Berg H, Rushworth MF, Bogdanovic MD, Kischka U, Wimalaratna S, Matthews PM. The role of ipsilateral premotor cortex in hand movement after stroke. Proc Natl Acad Sci U S A 2002; 99:14518- 14523.
- Kang N, Summers JJ, Cauraugh JH. Transcranial direct current stimulation facilitates motor learning post- stroke: a systematic review and meta-analysis. J Neurol Neurosurg Psychiatry. 2016 Apr;87(4):345-55.