References for this review were identified by searches of MEDLINE between 1969 and April 2006 and references from relevant articles. The search terms used were “brain stimulation”, “stroke”, “recovery”, “TMS”, “tDCS”, “plasticity”, “imaging”, “interhemispheric inhibition”, “intracortical inhibition”, “interhemispheric competition”. Abstracts and reports from meetings were also included. The final reference list was generated based on originality and relevance to the topics covered in the
Rapid ReviewNon-invasive brain stimulation: a new strategy to improve neurorehabilitation after stroke?
Introduction
Recovery of motor function after stroke is typically incomplete.1 6 months after the episode, two-thirds of stroke survivors are unable to take part in activities of daily living with their paretic hand to the extent they were before2 and only a few are able to carry out professional work.3 It remains a desirable goal to develop strategies to improve the beneficial effects of neurorehabilitative treatments.
Neuroimaging studies showed increased activity of M1intact hemisphere with movements of the paretic hand in patients with motor impairment.4, 5 The role of activity in the intact hemisphere on motor control, presently under investigation, varies depending on lesion site, time from stroke, and magnitude of impairment.6, 7 Patients with stroke experience changes in motor cortical excitability8, 9, 10, 11 and an abnormally high interhemispheric inhibition from M1intact hemisphere to M1lesioned hemisphere with movements of the paretic hand that is more prominent in cases with more substantial motor impairment.1 These findings, consistent with interhemispheric competition models of sensory and motor processing,12, 13, 14, 15 raised the hypothesis that purposeful modulation of excitability in motor regions of the intact and affected hemisphere may contribute to improvements in motor function.16
Recent studies in animals showed that motor recovery after focal lesions in the hand motor representation can improve with direct epidural cortical stimulation.17, 18, 19 The feasibility and safety of this invasive approach in patients is under investigation;20 an alternative approach is the use of non-invasive cortical stimulation.
Non-invasive brain stimulation is a powerful method to modulate human brain function.21, 22, 23 Transcranial magnetic stimulation is a painless procedure that modulates cortical excitability and has contributed to the understanding of mechanisms underlying cognitive processes.21, 24 The procedure involves a short strong electrical current that is delivered through an insulated coil of wire placed over the scalp (magnetic coil). The induced electrical currents modulate neuronal excitability at the stimulated sites. Depending on stimulation parameters, transcranial magnetic stimulation can upregulate or downregulate excitability to different extents25 in the neural structures under the stimulating coil.26 Transcranial direct-current stimulation is a procedure used to polarise brain regions through the non-invasive application of weak direct currents.23, 27, 28 The procedure elicits focal reversible shifts in cortical excitability depending on the polarity, strength, and duration of stimulation.28 Both techniques can purposefully modulate brain function, are painless and non-invasive, and can be used in double-blind, experimental designs27, 29, 30, 31, 32, 33, 34—although the mechanisms underlying these features may differ (panel22, 23, 27, 35, 36, 37, 38).
Interhemispheric competition models16 suggest possible strategies to influence function in the paretic hand (figure): upregulation of excitability in M1lesioned hemisphere and downregulation of excitability in M1intact hemisphere. In this paper we describe recent studies that report the effects of both transcranial magnetic stimulation and transcranial direct current stimulation on cortical excitability and motor function in the paretic hand after chronic stroke. Additional options under investigation include modulation of excitability in non-primary motor regions like the dorsal39, 40 and ventral41 premotor cortices or the supplementary motor area.
Section snippets
Upregulation of excitability in the affected hemisphere
Two non-invasive strategies have been used to increase excitability in the affected hemisphere: anodal transcranial direct current stimulation and rapid-rate transcranial magnetic stimulation (panel24, 26, 28, 35). Anodal transcranial direct current stimulation delivered to M1lesioned hemisphere was studied in patients with chronic stroke in sham-controlled double-blind crossover experimental designs.29, 30, 31 These studies showed improvements in performance of motor tasks that mimic
Where next?
Performance improvements reported so far with transcranial magnetic stimulation and transcranial direct current stimulation have been moderate in magnitude (10–30%) and, depending on the study, relatively transient. Implementation of repetitive stimulation and synchronous application with established rehabilitative treatments may lead to more prominent or longer lasting performance improvements. Areas for future investigation are the optimisation of parameters and sham controls, the role of
Search strategy and selection criteria
References (54)
- et al.
Post-stroke plastic reorganisation in the adult brain
Lancet Neurol
(2003) - et al.
Motor disinhibition in affected and unaffected hemisphere in the early period of recovery after stroke
Clin Neurophysiol
(2002) - et al.
Transcranial magnetic stimulation in cognitive neuroscience—virtual lesion, chronometry, and functional connectivity
Curr Opin Neurobiol
(2000) Transcranial direct current stimulation (tDCS)
Suppl Clin Neurophysiol
(2003)- et al.
Recharging cognition with DC brain polarization
Trends Cogn Sci
(2005) - et al.
Transcranial DC stimulation (tDCS): a tool for double-blind sham-controlled clinical studies in brain stimulation
Clin Neurophysiol
(2006) - et al.
Modulation of cortical excitability by weak direct current stimulation—technical, safety and functional aspects
Suppl Clin Neurophysiol
(2003) Risk and safety of repetitive transcranial magnetic stimulation: report and suggested guidelines from the International Workshop on the Safety of Repetitive Transcranial Magnetic Stimulation, June 5–7, 1996
Electroencephalogr Clin Neurophysiol
(1998)- et al.
Transcranial magnetic stimulation and stroke: a computer-based human model study
Neuroimage
(2006) - et al.
Modulation of excitability of human motor cortex (M1) by 1 Hz transcranial magnetic stimulation of the contralateral M1
Clin Neurophysiol
(2003)
Ipsilateral motor cortex activation on functional magnetic resonance imaging during unilateral hand movements is related to interhemispheric interactions
Neuroimage
Improved picture naming in chronic aphasia after TMS to part of right Broca's area: an open-protocol study
Brain Lang
Influence of interhemispheric interactions on motor function in chronic stroke
Ann Neurol
Epidemiology of ischemic stroke subtypes according to TOAST criteria: incidence, recurrence, and long-term survival in ischemic stroke subtypes: a population-based study
Stroke
Persisting consequences of stroke measured by the Stroke Impact Scale
Stroke
Neural correlates of motor recovery after stroke: a longitudinal fMRI study
Brain
Functional neuroimaging studies of motor recovery after stroke in adults: a review
Stroke
Mechanisms underlying recovery of motor function after stroke
Arch Neurol
Motor cortex disinhibition of the unaffected hemisphere after acute stroke
Muscle Nerve
Interhemispheric asymmetries of motor cortex excitability in the postacute stroke stage: a paired-pulse transcranial magnetic stimulation study
Stroke
Motor cortical disinhibition in the unaffected hemisphere after unilateral cortical stroke
Brain
Mechanisms of hemispheric interaction in man
Interhemispheric transfer of plasticity in the cerebral cortex
Science
Interhemispheric inhibition of the human motor cortex
J Physiol
Interaction of cortex and superior colliculus in mediation of visually guided behavior in the cat
Science
Paradoxical functional facilitation in brain-behaviour research. A critical review
Brain
Cortical electrical stimulation combined with rehabilitative training: enhanced functional recovery and dendritic plasticity following focal cortical ischemia in rats
Neurol Res
Cited by (685)
Non-invasive brain stimulation for functional recovery in animal models of stroke: A systematic review
2024, Neuroscience and Biobehavioral ReviewsSomatosensory evoked potentials amplitude is enhanced after non-invasive brain stimulation in chronic ischemic stroke: Preliminary results from a randomised control trial
2024, Journal of Stroke and Cerebrovascular DiseasesState-dependent interhemispheric inhibition reveals individual differences in motor behavior in chronic stroke
2023, Clinical Neurophysiology