The cortical silent period is shortened in migraine with aura

Central neuronal hyperexcitability may be the physiological disturbance that predisposes subjects to migraine attacks. To test this hypothesis, we studied the cortical stimulation silent period (CSSP) elicited by transcranial magnetic stimulation (TMS), which is in part a measure of central inhibition of motor pathways in migraine with aura (MwA) patients and normal controls.

In nine MwA patients (mean age 35.9 +/- 7) and 9 controls (mean age 37.6 +/- 7), we carried out transcranial stimulation using a 95 mm circular coil and Caldwell MES 10 stimulator to determine resting motor threshold (MT) for bilateral FDI muscles. All subjects performed isometric voluntary contraction of bilateral FDI maintained at 20% of maximal effort, during which we measured bilateral CSSP at (i) the stimulus intensity (SI) determined for the MT and (ii) an SI of 1.5 x MT.

Although the mean MT was higher in MwA compared with controls (63.1 +/- 14.4 vs 58.1 +/- 8.9), the difference was not significant. At an SI of 1.5 x MT the mean CSSP did not differ between the groups (MwA 141.7 +/- 31.9 vs controls 162.4 +/- 36.6). At the SI of the MT, however, the CSSP was shorter in MwA patients than in controls (62.9 +/- 27.3 vs 106.3 +/- 19.6, p = 0.001). There was an inverse correlation between the duration of CSSP and an increased frequency of headache (p = 0.02).

The shortened CSSP that we measured in MWA patients compared to normal with low intensity magnetic stimulation suggests reduced central inhibition resulting in increased excitability of cortical neurons in migraine subjects. The association of CSSP reduction with increased frequency of migraine is further suggestive that brain excitability is the basis of susceptibility to migraine attacks.