Various studies have aimed to explore the potential of non-invasive brain stimulation
techniques such as transcranial direct current stimulation (tDCS) to promote motor
recovery after stroke. After promising results from early proof-of-concept studies,
particularly for the stimulation of the primary motor cortex (M1), it has become evident
that the translation from scientific to clinical application is challenging. Aiming to
uncover alternative stimulation targets, the cortico-cerebellar network and cerebellar
brain stimulation have gained an increasing interest in the field of neurorehabilitation.
However, large inter-study and inter-subject variability in behavioural responses to tDCS
indicated that a one-size-fits-all approach might not lead to sufficient effect sizes in
clinical populations. As structural and functional brain imaging has significantly
evolved to powerful tools to assess distinct neuronal networks, such as the
cortico-cerebellar network, in individual stroke patients and to infer
structure-function-behaviour-relationships, the question arises whether such information
might serve as imaging biomarkers to inform about the treatment responsiveness to
non-invasive brain stimulation.
The present study will evaluate the potential of cortico-cerebellar network properties in
a group of chronic stroke patients and healthy participants to explain inter-subject
variability in responsiveness to two brain stimulation approaches targeting the
cortico-spinal and cortico-cerebellar network: 1) cortical M1 tDCS, 2) combined M1 and
cerebellar tDCS. Participants will be examined clinically and by structural and
functional MRI. Structural MRI will be used to primarily reconstruct cortico-spinal and
cortico-cerebellar motor tracts. Tract-related diffusion-based parameters will be used to
infer microstructural network integrity. Resting-state MRI will be acquired to assess
functional network connectivity. The behavioural impact of the tDCS will be evaluated
during a multi-session structured motor training paradigm over seven days.
Recruitment:
Early- or late chronic stroke patients who have a persistent upper extremity deficit.
Treatment/Intervention:
Three tDCS montages combined with 7 days of physiotherapy (45min per session) will be
applied to chronic stroke patients in a double-blinded, parallel group design. The
following montages will be tested: anodal ipsilesional M1-stimulation with 2mA, anodal
ipsilesion M1-stimulation combined with anodal contralesional cerebellar stimulation with
2mA per anode and a sham stimulation. The stimulation will be applied for the first 20min
of physiotherapy.
Evaluation/Measurement:
Prior to the intervention, patients will receive functional testing and a MRI scan. 7
days after physiotherapy, functional testing will be performed again. Functional tests
include: NIH Stroke Scale (NIHSS), Fugl Meyer Assessment of the upper limb (FMA), Wolf
Motor Function Test (WMFT), Jebsen Taylor Hand Function Test (JTT), Nine-Hole-Peg-Test
(NHP), Mini-Mental-State Examination.
Analyses:
Statistics will be conducted to relate neuroimaging-based network properties of the
cortico-spinal and cortico-cerebellar network to the treatment gains under tDCS combined
with motor training (primary outcome). Importantly, group differences regarding the
behavioural effects of the verum and sham condition will serve as secondary outcomes.