Exploring the influence of vigilance state on MEP amplitude induced by TMS

Stroke is a frequent cause of upper limb motor impairment. Currently,
Transcranial Magnetic stimulation (TMS) is used to determine the presence or
absence of motor evoked potentials (MEPs) and its relation to outcome in
stroke. So far, few studies have employed the amplitude of MEPs for prognosis
due to inherent intraindividual variability in MEP amplitude. Earlier research
suggested that vigilance variations may be a source of MEP amplitude
variability. We therefore hypothesize that by stabilizing vigilance,
intraindividual MEP amplitude variability may be reduced and therefore
reproducibility will be increased.
Furthermore, in patients with myelopathy, decisions to perform an operative
intervention are not easily made solely based on MRI data. Often, multiple
lesions are visible on MRI, but the specific lesion causing clinical symptoms
cannot be identified. On the other hand, abnormalities that seem harmless may
be causing the patient discomfort, as well. MEP measurements are then used in
addition to radiological evidence (or non-evidence) to find the source of the
patient*s functional problems. In this application, only MEP presence/absence
is assessed and MEP amplitude is so far not taken into account, either. This
group of patients therefore forms another elected group of subjects to
incorporate in this study.

The primary objective is to investigate the influence of vigilance state on MEP
amplitude in healthy adults.
Secondary objectives are to develop a paradigm to stabilize vigilance state
resulting in lower MEP amplitude variability in healthy adults and to test the
feasibility and results of this paradigm in stroke patients in the first week
after stroke and in myelopathy patients.

Healthy participants will be subjected to MEP and EEG measurements. Stroke
patients and myelopathy patients will only be subjected to MEP measurements.

Healthy participants will undergo six MEP measurements performed in a single
session. In each measurement, 20 measurable MEPs will be evoked. At the start
of this session EMG surface electrodes will be attached to the first dorsal
interosseous muscle (FDI), both left and right, for the measurement of
electrical muscle activity and an EEG cap will be placed on the head of the
participant for measuring electrical brain activity as a measure of vigilance.
The first three measurement will be conducted according to the regular MEP
paradigm. The first of these three measurements will be done using the circular
coil placed on the vertex, during the other two (one for each hemisphere)
measurements the figure-8 coil will be used. The second three measurements will
be done according to the newly designed vigilance stabilizing paradigm. The
first of these three measurements will be performed using the circular coil. In
the remaining two measurements (one for each hemisphere) the figure-8 coil will
be used. This new paradigm will be developed in a pilot group of healthy
participants. Only when the new paradigm will result in lower MEP variability
in healthy participants, the measurements in stroke patients and myelopathy
patients will be pursued.

Stroke patients and myelopathy patients will undergo two MEP measurements (one
for each hemisphere) using the new paradigm for minimizing influence of
vigilance state. Each measurement will consist of 20 consecutive MEP
measurements. At the start of the measurement session, EMG surface electrodes
will be placed on the FDI muscle, both left and right.

TMS stimulation does not involve risks when common exclusion criteria are
applied. Healthy participants will undergo a measurement session of
approximately two hours (MEP with EEG). Patients will undergo a measurement
session of approximately one hour (MEP only). No personal benefit to the
participants is derived from this study, however participation in this study
may improve diagnostic and prognostic methods for various neurological
disorders in the future.