Intra-subject reliability of non-invasive brain stimulation on lower limb motor control

Transcranial direct current stimulation (tDCS) is a method that is used in
recent studies to increase the excitability of the cortex. This increase in
excitability can have a positive effect on the motor control and learning in
healthy subjects as well as on the recovery of stroke patients. Although
studies have shown large effects of >30% increase in excitability, there is
also a large variability between subjects. Moreover, it is not known what the
reproducibility of these effects in individual subjects is.

The objective is to assess the intra-subject reliability of tDCS induced
effects on the reaction time in the lower extremities of healthy subjects.

This is a double blind and randomised cross-over study. All subjects
participate in 5 experimental sessions separated by at least two days. In all
sessions both subjects and raters will be blinded to the applied intervention.
The order of interventions will be randomized across subjects.

In each of the five experimental sessions, one of three types of anodal
stimulation will be applied. The forms involve one time sham (placebo)
stimulation, twice conventional anodal continuous tDCS (ac-TDCS) and twice
anodal pulsed stimulation (ap-TDCS). The stimulation will be applied for 10
minutes. We will determine the effect of this intervention on the reaction
time. The reaction time of ankle movement in response to a visual signal will
be assessed before (baseline) and three times after the stimulation (post);
after 5 min, 30 min, and 60 min.

Participants will have to visit the laboratory five times with a minimum of two
days between the different visits. Each of the sessions will take about 1 hour
and 45 minutes. The applied technique to modulate motor cortex excitability is
generally well tolerated and has only been associated with relatively minor
adverse effects in healthy humans and neurological patients, such as mild
headache, moderate fatigue, nausea and an itching sensation as well as skin
irritation under the electrodes.
The healthy subjects will likely not have any direct benefit from
participation. We do not expect that the stimulation results in any long
lasting effects. It is of importance to conduct this study to know what the
intra-subject reliability of tDCS is and to be able to interpret differences in
effects caused by different forms of tDCS. Furthermore, if there is
considerable intra-subject variability, the next step will be to try to
identify the factors that contribute to this variability.