Brain Trauma Stroke Figure 3: Simplified Model of the Imbalance in Interhemispheric Interactions after Stroke and Therapeutic Options

Anodal TDCS

Cathodal TDCS

The inhibitory influence of ipsilesional onto contralesional motor cortex is decreased, which in turn leads to a disinhibition of contralesional motor cortex (left). Non-invasive transcranial direct current stimulation (TDCS) provides two therapeutic options aiming at ‘re-balancing’ this imbalance. Upregulation of excitability of the ipsilesional motor cortex spared by the stroke (middle) and downregulation of excitability of the contralesional motor cortex (right). Source: Schlaug et al., 2008.41

Figure 4: Abnormal Activation Pattern Related to Passive Elbow Movements in Chronic Stroke Patients with Severe Spastic Hemiparesis (A)

A B 1.0 0.0

14 Session

2 C 1.0 3

connections provide a framework for hypotheses based on two facets: upregulating excitability of intact portions of the ipsilesional motor cortex, and downregulating excitability of the contralesional motor cortex. The contralesional cortex is presumed to be disinhibited due to the lack of an inhibitory influence from the lesional motor cortex while at the same time it exerts an unbalanced inhibitory influence on the lesioned motor region. The downregulation of the contralesional, disinhibited motor regions is presumed to counter an abnormal inhibitory influence on ipsilesional regions (see Figure 3).41,53,80

Pilot

studies, using either rapid transcranial magnetic stimulation (rTMS)81–84 or transcranial direct cortical stimulation (tDCS),85–88

have shown that 0.0

14 Session

2 3

Passive elbow movements induced a bilateral activation in sensorimotor cortex. However, movements of the affected arm showed a smaller activation in the ipsilesional hemisphere than movements of the non-affected arm in the contralesional hemisphere. Also, movements of the affected arm showed greater ipsilateral activation than movements of the non-affected arm. Patients with residual movement activity showed an increase of the fMRI-signal in the dorsal portion of the ipsilesional motor cortex following combined botulinum toxin (BTX) and cycling arm training both in relation to passive movements of the affected and non-affected arm (B). In contrast, patients with complete hemiplegia showed a similar training effect only for the affected arm but not for the non-affected arm, which was possibly due to an interhemispheric disconnection resulting from the infarct lesion (c). Source: Diserens et al., 2010.98

premotor and parietal cortices in both cerebral hemispheres. Similarly, a daily treatment with observing actions combined with physical training for four weeks resulted in a significant increase in motor functions that lasted for at least eight weeks after training.78

This was associated with

a significant overactivation compared with the control group in ventral premotor cortices, superior temporal gyri, the supplementary motor area and supramarginal gyrus related to an object manipulation task. However, it must be mentioned that the capacity to perform motor imagery can be weakened by limb loss or disuse, although the temporal characteristics of motor imagery may be not affected.79

Brain Stimulation as an Add-on to Peripheral Sensorimotor Activities In the context of experimental rehabilitative therapies, the model of interhemispheric imbalance and the important role of transcallosal

70

these approaches can improve motor impairment, at least transiently, and that the combination of central stimulation and peripheral sensorimotor activities and training seems to enhance these effects. The efficacy of upregulating ipsilesional motor cortex can be related to its plastic effects on tissue spared by the stroke. As mentioned above, the potential of perilesional tissue for post-stroke recovery has been demonstrated using functional imaging and electrophysiological methods. Accordingly, rTMS yielded therapeutic responses only when at least parts of the motor cortex were spared by the stroke.81 Furthermore, the therapeutic response to anodal tDCS and simultaneous robotic arm therapy was relatively small in patients with extensive hemispheric lesions including the motor cortex.87

It has been

argued that, when using large electrodes to target functionally intact perilesional tissue, tDCS can exert its effects not only on the primary motor cortex, but also on adjacent premotor and sensory regions.41 Modulating excitability of such regions, which have previously been shown to play an important role for motor recovery,89,90 to the efficacy of tDCS.91

may contribute Furthermore, it was shown that the

enhancing effects of anodal stimulation on the intact portions of the ipsilesional motor cortex85,88

modulation of inter-hemispheric interactions92 of cathodal stimulation on the contralesional motor cortex.86

may be potentiated through additional via a suppressive effect A study in

healthy subjects suggested that bihemispheric tDCS (upregulation of affected motor cortex and downregulation of contralateral motor cortex at the same time) produces greater behavioural effects than uni-hemispheric stimulation.93

Accordingly, this novel bihemispheric

tDCS therapy with simultaneous physical/occupational therapy for five consecutive days yielded substantial functional improvements that were significantly greater than in a placebo group receiving only physical or occupational therapy.91

EUROPEAN NEUROLOGICAL REVIEW

Mean BOLD activity

Mean BOLD activity