Early Neurophysiological Interventions in Acute Cerebral Lesions

Transcranial direct current stimulation (tDCS) is a form of noninvasive brain stimulation used to induce excitability changes in central nervous system circuits. The basis of tDCS application in stroke patients follows the model of interhemispheric imbalance between the damaged and intact hemispheres: anodal tDCS over affected hemisphere to induce long-lasting increase in cortical excitability, cathodal tDCS over unaffected hemisphere to induce long-lasting decrease in cortical excitability. Simultaneous effects on both hemispheres can be obtained with bi-hemispheric tDCS. Minimum intensity and duration of tDCS is necessary to induce long-lasting effects, which are referred as long-term potentiation and long-term depression.

Most interventional tDCS studies have focused on chronic stroke patients, at a time in which patients are supposed to have reached a plateau in their spontaneous recovery after the lesion. Less research has evaluated the effects of an early tDCS intervention. tDCS protocols differ in location of electrodes, session frequency and duration, dosage of electrical charge, temporal window of tDCS delivery and other variables. The functional benefit of tDCS may increase with the concomitant application of adjuvant therapeutic strategies such as constraint-induced therapy, electrical stimulation or robot-mediated therapy. Sattler et al. used radial nerve stimulation, together with tDCS, to facilitate motor output. It is possible that repetitive peripheral nerve stimulation (rPNS) modulates corticospinal output at somatotopically specific supraspinal sites through GABAergic interneurons. The patients that improved in Sattler et al.'s study, as in other tDCS studies, had an initial mild to moderate impairment of motor function. Improvement is more dubious in patients presenting with severe motor deficit.

Our aim in this study was to examine the effectiveness of bihemispheric tDCS combined with rPNS in acute stroke patients with pronounced motor impairment, the group of patients with fewer options in therapeutic programs.

The benefit of applying tDCS early after stroke is still unclear. However, based on animal models, the first month after stroke seems to be the optimal period to induce morphological changes associated with increased plasticity, hence the therapeutic window was chosen between 5 and 20 days after the stroke event. The investigators reasoned that, if plastic changes have been induced by tDCS, the clinical and neurophysiological benefit may manifest not just immediately after treatment, but further ahead in the patient's natural evolution after the stroke. For this reason, the investigators considered relevant to determine if the results of tDCS treatment persisted in time and had a long-term effect, therefore extended our clinical and neurophysiological follow-up to 12 months after treatment.

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