Improving transcranial direct current stimulation by targeting the motor network

About 80% of stroke patients suffer motor impairments. The first months of
rehabilitation are critical to regain motor function and avoid limitations in
mobility. Therefore, optimising the effects of early motor therapy in stroke
patients is crucial for their quality of life. Transcranial Direct Current
Stimulation (tDCS) is a form of non-invasive electric stimulation where a weak
current is applied through electrodes on the scalp. The effectiveness and
working mechanism of tDCS is not yet completely known, but numerous studies
demonstrate positive effects on cortical excitability and motor learning.

Recently, a multi-electrode array to stimulate the entire motor network was
proposed and found to introduce higher motor evokted potential amplitudes than
the conventional way of stimulation. In the present study, we would like to
reproduce these results in a larger sample of the healthy population.
Additionally, we would like to investigate the relation between background
cortical activity and the magnitude of the cortical excitability. Furthermore,
we would like to investigate the effect of tDCS on brain activity and motor
learning. The study will give guidelines on the steps to take to improve the
effectiveness of tDCS in motor recovery after stroke.

To investigate if conventional tDCS can be improved by using a new electrode
configuration. To find a relation between ongoing EEG and MEP magnitude. To
investigate the effect of tDCS on cortical excitability (measured with TMS),
brain activity (recorded with EEG) and motor learning.

Single-blinded, randomised repeated-measures design

Participant 21 to 55: Subjects receive conventional, motor network or sham
network tDCS over the motor cortex for 10 minutes at an intensity of no more
than 2 mA per electrode and at most 4 mA in total in the sessions where
cortical excitability is assessed. Subjects receive conventional, motor network
or sham network tDCS over the motor cortex for 10 minutes at an intensity of no
more than 2 mA per electrode and at most 4 mA in total.

Participant 56 to 105:
Subjects receive conventional, motor network or sham network tDCS over the
motor cortex for 10 minutes at an intensity of no more than 2 mA per electrode
and at most 4 mA in total.

Participant 1 to 20:
Participants are asked to visit the Erasmus MC once for 2.5 hours. During the
experimental session, EEG and EMG are applied, after which test subjects
perform the motor task for about 90 minutes. The burden on the participants is
small. During the motor task, participants have the opportunity to pause if
they need it. Participants are compensated for travel expenses and additionally
receive financial compensation for participation.

Participant 21 to 55:
Participants are asked to provide a saliva sample for BDNF analysis,
demonstrated to be a determinant for tDCS effectiveness, and have to visit the
Erasmus Medical Centre up to three times for the different stimulation
configurations. Each session takes up to 150 minutes. During each session,
subjects will receive conventional, motor network or sham network stimulation
over the motor cortex. TDCS is reported to be safe; side effects are mild.
Transcranial magnetic sitmulation (TMS) has been proven to be a safe method.
There is little to no risk involved in the application of single pulse TMS.
Discomfort can be experienced by the participants due to the muscle twitches
and sounds generated by TMS. There will be financial compensation for travel
expenses and participation.

Participant 56 to 105:
Participants are asked to visit the Erasmus MC three times. Each session takes
up to 2.5 hours. During the first session, participants are asked to provide a
saliva sample for BDNF analysis, because it is demonstrated that the BDNF
polymorphism can be a determinant for tDCS effectiveness. During the
experimental session, EEG, EMG and EOG are applied and participants are asked
to execute a motor learning task, which takes approximately 45 minutes. The
burden on the participants is small. During the motor learning task,
participants have the opportunity to pause if they need it. During each
session, subjects will receive conventional, motor network or sham network
stimulation over the motor cortex. tDCS is reported to be safe; side effects
are mild. Participants are compensated for travel expenses and additionally
receive financial compensation for participation.