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Resting Motor Threshold, MEP and TEP Variability During Daytime

Resting Motor Threshold, MEP and TEP Variability During Daytime

Esther M. ter Braack, Annika A. de Goede, Michel J. A. M. van Putten
Brain Topography

Humans show a variation in physiological processes during the day. To
reliably assess (changes in) cortical excitability with transcranial
magnetic stimulation (TMS), it is relevant to know the natural variation
in TMS readouts during the day. In case of significant daytime
variations, this should be taken into account when scheduling
(follow-up) measurements. This study aims to evaluate the influence of
the time of day on the resting motor threshold (RMT), motor evoked
potential (MEP) and TMS evoked potential (TEP) in healthy controls.
TMS–EMG–EEG was recorded in 16 healthy subjects. At both motor cortices,
we administered 75 pulses at an intensity of 110% RMT. Subjects were
stimulated during five sessions in one day (8:00 AM, 10:30 AM, 1:00 PM,
3:30 PM and 6:00 PM) while keeping the stimulation intensity constant.
We compared the TEP waveforms between the five sessions with a
cluster-based permutation analysis, and the RMT and MEP amplitude with
rmANOVA. In general there were no significant differences between the
five sessions in the RMT, MEP amplitude or TEP. Only for the left side,
N100 amplitude was larger at 3:30 PM than 10:30 AM. The standard
deviation of the P30 and N100 amplitude was significantly higher between
subjects within one session than within single subjects during the day.
The TEP is highly reproducible during the day, with a low
intra-individual variation compared to the inter-individual variation.
In addition, we found no significant variation of the RMT and MEP
amplitude between multiple sessions on one day.

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