Enhancing transcranial direct current stimulation via motor imagery and kinesthetic illusion: crossing internal and external tools
Bodranghien et al. Journal of NeuroEngineering and Rehabilitation
Enhancing transcranial direct current stimulation via motor imagery and kinesthetic illusion: crossing internal and external tools
Florian Bodranghien 2
Mario Manto 1 2 3
Florent Lebon 0 4
0 Laboratoire INSERM U1093 Cognition, Action et Plasticité Sensorimotrice, Université de Bourgogne Franche-Comté , Dijon , France
1 Service des Neurosciences, Université de Mons , Mons , Belgium
2 Unité d'Etude du Mouvement, Laboratoire de Neurologie Expérimentale, ULB , Brussels , Belgium
3 UEM, FNRS-ULB , 808 Route de Lennik, 1070 Bruxelles , Belgium
4 UFR STAPS, Université de Bourgogne Franche-Comté , Dijon , France
Background: Transcranial direct current stimulation is a safe technique which is now part of the therapeutic armamentarium for the neuromodulation of motor functions and cognitive operations. It is currently considered that tDCS is an intervention that might promote functional recovery after a lesion in the central nervous system, thus reducing long-term disability and associated socio-economic burden. Discussion: A recent study shows that kinesthetic illusion and motor imagery prolong the effects of tDCS on corticospinal excitability, overcoming one of the limitations of this intervention. Conclusion: Because changes in excitability anticipate changes in structural plasticity in the CNS, this interesting multi-modal approach might very soon find applications in neurorehabilitation.
Direct current stimulation; Motor imagery; Kinesthetic illusion; Excitability; Rehabilitation
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Transcranial direct current stimulation (tDCS) is a
noninvasive brain stimulation technique, which consists of
delivering a low (usually between 1 and 2.5 mA)
constant current between two electrodes positioned on the
skull. Depending on the polarity chosen, tDCS is either
cathodal or anodal. In the first set up, the cathodal
electrode is positioned over the target brain area and
lowers the underlying neurons’ action potential firing
rate, therefore decreasing neural excitability. In the
second set up, the anodal electrode is positioned over
the target area and increases the action potential firing
rate, therefore inducing a hyperexcitability [
3
]. The
socalled after-effects depend on the set up, the duration and
the intensity of the stimulation [
11
]. For anodal DCS, the
intra-DCS effects are much less prominent when
compared to the after-effects. However, for cathodal DCS,
the intra-DCS effects and the after-effects are nearly
similar [
16
]. One of the limitations of DCS is related to
the fact that the after-effects will disappear after a few
hours, hence the importance of repeating the application
in the following days or weeks. Despite this limitation, due
to its ease of use, its safety and its low cost, tDCS is
growingly applied to modulate central nervous system
(CNS) excitability in fundamental research [
19
] as well as
in trials involving human healthy volunteers or patients
[
2
]. In particular, there is a great hope that tDCS will be
helpful not only for the acute management or
rehabilitation of motor neurological disorders, but even beyond, for
instance in cognitive or psychiatric disorders, although
optimizations of the stimulation parameters are still
clearly required [
7, 13
].
While tDCS artificially modulates neural excitability,
other methods use afferent inputs or even internal
representations of movement to induce cortical
plasticity. Kinesthetic illusion (KI) is based on various sources
of sensory stimuli to activate cerebral networks. For
example, a hand motion video, if positioned
appropriately, induces the subjective feeling of movement in
one’s hand [
9
]. It is usually assumed that the right
cerebral hemisphere plays a critical role in the conscious
experience of the body. This is confirmed by recent fMRI
studies demonstrating that kinesthetic illusory
movement activates the right frontoparietal regions [
1
].
Considered globally, investigations of proprioceptive bodily
illusions show a hierarchy of three brain systems: the
motor network processing afferent inputs from skeletal
muscles in order to build kinematic/dynamic postural
models of limbs, parietal regions integrating the
information across different coordinate systems in order to
maintain the adaptability of the body representation, and
the right inferior fronto-parietal network recruited when
bodily illusions are concerned [
14
]. One of the potential
clinical applications of KIs in the coming years is the
management of painful states [
4
].
Interestingly, motor imagery (MI), the internal
representation of movement without concomitant
contraction, induces similar brain activation as the actual
motor performance [
17
]. These neuroanatomical
correlates legitimate the benefits of MI-based mental
practice on motor learning [
8
]. MI-based motor
learning impacts on brain networks, especially the
functional connectivity of the default mode network [ (...truncated)