Abstract
IntroductionConnectivity within the primary motor cortex can be measured using the paired-pulse transcranial magnetic stimulation (TMS) paradigm. This evaluates the effect of a first conditioning stimulus on the motor evoked potential (MEP) elicited by a second test stimulus when different interstimulus intervals are used. Aim of the present study was to provide, in patients suffering from migraine without aura (MwoA), additional information on intracortical facilitation (ICF), short intracortical inhibition (SICI), and long intracortical inhibition (LICI), using different intensities of the test stimulus (TS).MethodsWe enrolled 24 patients with episodic MwoA and 24 age- and sex-matched healthy volunteers. Both patients and controls were randomly assigned to two different experimental groups: the first group underwent evaluation of ICF, while in the second group we assessed SICI and LICI. All these measures were assessed by using three different suprathreshold intensities of the TS (110%, 130% and 150% of the resting motor threshold, RMT). Interstimulus intervals (ISIs) of 10 ms were used for testing ICF, while SICI and LICI were carried out by using 2 ms and 100 ms ISIs respectively. All migraine patients underwent the experimental protocol while in the interictal pain-free state.ResultsA main finding of the study was that an increased ICF could be seen in migraineurs as compared to the healthy subjects only by using a 110% intensity of the TS. Instead, no significant differences were observed between patients and controls as regards both measures of intracortical inhibition.ConclusionWe show that hyperresponsivity of the glutamatergic intracortical circuits can be detected in the migraine motor cortex only by applying a low suprathreshold intensity of stimulation. Our results strengthen the notion that, to be reliable, the assessment of cortical excitability in migraine should always include evaluation of the cortical response to different stimulation intensities.
Highlights
Connectivity within the primary motor cortex can be measured using the paired-pulse transcranial magnetic stimulation (TMS) paradigm
The main aim of the present study was to provide additional information on intracortical inhibition (SICI and long intracortical inhibition (LICI)) and facilitation (ICF) using different intensities of the test stimulus in patients suffering from migraine without aura (MwoA)
Post-hoc analysis showed that intracortical facilitation (ICF) assessed at stimulus intensity of 110% of the Resting motor threshold (RMT) was more pronounced in the patients group with respect to the healthy volunteers (p = .014), whilst no significant differences were observed for the other test stimulation intensities
Summary
Connectivity within the primary motor cortex can be measured using the paired-pulse transcranial magnetic stimulation (TMS) paradigm. Aim of the present study was to provide, in patients suffering from migraine without aura (MwoA), additional information on intracortical facilitation (ICF), short intracortical inhibition (SICI), and long intracortical inhibition (LICI), using different intensities of the test stimulus (TS). As regards the paired-pulse TMS paradigm, it has been shown that changes in the intensity of the test stimulus have a considerable effect on measures of cortical inhibition and facilitation in the healthy subjects [14, 15] On these bases, the main aim of the present study was to provide additional information on intracortical inhibition (SICI and LICI) and facilitation (ICF) using different intensities of the test stimulus in patients suffering from migraine without aura (MwoA)
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