The offline effects of transcranial direct current stimulation (tDCS) on postural balance control after stroke.

In people after stroke, responses to external perturbations are delayed, which
is a main risk factor for falling. In the last decades, transcranial direct
current stimulation (tDCS) has been shown to facilitate executed movements in
stroke survivors. However, this has almost exclusively been studied in upper
extremity movements. In young adults, tDCS has recently been shown to
facilitate balance recovery responses in the lower extremities as well. This
study will investigate to what extent the latter results also apply to people
after stroke. In this population, a wide variability in effects of tDCS is
reported for upper extremity movements, which is expected to be due to the
amount of cortical integrity after the CVA. Therefore, this study will also
investigate the relation between the effects of two types of stimulation
(anodal over the affected hemisphere, and cathodal over the unaffected
hemisphere) and MRI obtained values for cortical integrity of the motor
regions.

The objective of this study is twofold.
One aim of the study is to investigate the effects of tDCS (anodal, cathodal
and sham) on balance correcting responses and simple reaction times in lower
extremity muscles. We will determine whether the effects of tDCS are different
between people after stroke and healthy controls (within similar age range and
in young controls).
Another goal is to investigate whether neuroimaging based measures of integrity
of neural motor pathways can explain the anticipated variability of
tDCS-induced effects in people after stroke.

randomized single-blind sham-controlled cross-over study

Participants will not directly benefit from their participation in the study.
MRI scans are painless and safe. MRI is a technique without radiation (unlike
x-ray and CT scans). In case of unexpected findings, the participant will be
informed by his physician. Transcranial direct current stimulation (tDCS) is a
widely used non-invasive brain stimulation technique, applying weak direct
currents via conductive sponge electrodes to the scalp. These weak currents can
slightly shift the neurons* membrane potential and thereby increase or decrease
spontaneous neuronal activity in the stimulated cortex, but (unlike TMS) they
do not evoke action potentials. During the stimulation, participants may
transiently experience light tingling, itching or burning sensations on the
skin underlying the electrodes, which can be unpleasant. The most common side
effects are a light transient headache and a feeling of fatigue. In the current
study, participants will be stimulated with a protocol that is considered safe
with respect to the latest published safety guidelines. All subjects are
screened for their relevant medical history and other tDCS safety aspects (e.g.
metal parts in the head, skin allergies). Postural responses will be assessed
on the Radboud Falls Simulator. Participants will be exposed to balance
perturbations by sudden translations of the support surface. There are no risks
of participating in the balance assessment, since rails are mounted around the
balance platform and participants wear a safety harness. From previous studies
at our department, we know that people (after a CVA) should be able to overcome
the balance perturbations at the proposed intensity. In summary, because the
risk is negligible and the burden associated with participation can be
considered minimal, we do not expect serious adverse events due to the project.