Despite intensive neurophysiological research, evidence is lacking to show whether abnormal cortical excitability in migraine reflects a primary cortical disturbance or reduced control by thalamo-cortical loops. One way to contribute to the scientific discussion on this topic is to deliver transcranial magnetic stimulation (TMS) and test the cortical silent period (SP) recorded in facial muscles. The facial-muscle SP is a purely cortical phenomenon that reflects the excitability of inhibitory interneurons, and can disclose changes in cortical inhibition even in patients without documented primary lesions of the motor cortices. To test the interictal excitability of cortical motor inhibitory interneurons in migraine, we investigated the facial-SP in patients with migraine with and without aura between attacks. In 26 patients and 15 age-matched controls, high-intensity magnetic stimuli were delivered with a round coil centered at the vertex during a maximal muscle contraction. Electromyographic responses were recorded from surface electrodes placed over the subjects’ perioral muscles. Facial SPs were significantly shorter in patients than in controls. The SP shortening provides neurophysiological evidence showing hypoexcitability of cortical inhibitory neurons in patients with migraine between attacks. Despite a possible primary deficit of cortical inhibitory interneurons in migraine, we favor the interpretation of a secondary disfacilitation by hypoactive thalamo-cortical loops. Based on this interpretation, the interictal reduced cortical inhibition documented by the shortened SP could be considered the motor counterpart of the reduced preactivation excitability level in the sensory cortices purported to explain why cortical evoked responses habituate poorly in patients with migraine.
aDepartment of Neurological Sciences, La Sapienza University, Rome, Italy
bOspedale A. Fiorini, Terracina, LT, Italy
cDepartment of Neurology and Otolaryngology, La Sapienza University, Rome, Italy
dICOT – Istituto Chirurgico Ortopedico Traumatologico, Latina, Italy
eIRCCS Neuromed, Pozzilli, IS, Italy
fG.B. Bietti Eye Foundation-IRCCS, Dept of Neurophysiology of Vision and Neurophthalmology, Rome, Italy
gDepartment of Neurological, Motor and Sensorial Sciences, IRCCS San Raffaele, Rome, Italy
hIRCCS Fondazione Santa Lucia, Rome, Italy
iMolecular Genetics Laboratory, IRCCS “C. Mondino” Institute of Neurology Foundation – IRCCS San Raffaele, Rome, Italy
*Corresponding author. Tel.: +39 0773 6556211; fax: +39 0773 6553601.
Submitted February 9, 2007; received in revised form April 22, 2007; accepted May 10, 2007.