TMS response in healthy subjects.

Rationale:

The diagnostic process in epilepsy is often time-consuming due to the limited sensitivity and the nature of standard EEG recordings. TMS-EEG is a candidate tool to significantly improve the diagnostic efficiency in epilepsy. In this study, we will perform initial measurements in healthy volunteers to evaluate the normal variation and the presence of a circadian rhythm in TMS-EEG responses.



Objective:

The main objective is to explore and quantify the variability and reproducibility of MEP and EEG responses after single pulse TMS in healthy subjects.



Study design:

Interventional study.



Study population:

20 Healthy, right-handed volunteers, age between 18 and 60 years, who do not take pro-epileptogenic medication or drugs and without a personal history of epilepsy.



Intervention:

Five single pulse TMS sessions during 1 day.



Main study parameters/endpoints:

Variability and reproducibility of MEP (Motor Evoked Potential: amplitude, latency) and EEG response (electroencephalography response: amplitude, latency, frequency content) for 3 different brain areas.

Before we focus our research on TMS-EEG experiments in epilepsy patients, we first aim to learn more about the characteristics and intra-subject variability of the TMS-EEG and MEP response in healthy subjects.



In addition, we will evaluate if TMS-EEG and MEP responses show a circadian rhythm. Although this was explored in a previous study [Koski 2005], no definite conclusions were drawn, possibly due to significant variability in the measurements due to inaccurate (re-)positioning of the magnetic coil. We expect to confirm or reject the presence of a circadian rhythm of the motor threshold. Clearly, the presence or absence of a circadian rhythm is relevant for subsequent measurements in patients, as this may interfere with variations due to epilepsy.

Subjects will receive an MRI of the head prior to the TMS experiment. During the day of the experiment, the subject will undergo 5 TMS sessions during the day (8:00 AM - 10:30AM - 13:00 PM - 15:30PM - 18:00 PM). Five subjects will return 1 week after the day of the experiments for an additional TMS session.

Our Transcranial Magnetic Stimulation equipment has a maximum output of 1,5 Tesla. Pulse duration is 400 microsec. 50 single TMS pulses will be given to 6 different brain areas (3 on each hemisphere) while the EMG and EEG are recorded.



First, the hot spot and motor threshold of the right extensor digiti minimi (EDM) will be determined. Then, we stimulate the 3 brain areas on the left hemisphere with 110% of motor threshold. Measurements are then repeated for the right hemisphere. Pulses will be given with a frequency of ~0.25 Hz (single pulse TMS).