Facilitatory effects of 1 Hz rTMS in motor cortex of patients affected by migraine with aura

We previously showed paradoxical facilitatory effects of low-frequency repetitive transcranial magnetic stimulation (rTMS) on striate and extrastriate cortex of patients suffering migraine with aura. In this study we evaluated the effects of 1 Hz rTMS on the excitability of inhibitory and facilitatory circuits of motor cortex to explore whether the abnormal pattern of excitability extends beyond the sensory cortex also involving motor areas in migraine with aura. Nine patients affected by migraine with aura and eight healthy controls entered into the study. The hot spot for activation of the right abductor pollicis brevis (APB) was checked by means of a figure-of-eight coil and motor threshold (MT) recorded on this point. Nine hundred magnetic stimuli at 1 Hz frequency and 90% MT intensity were delivered at the hot spot. Before and after rTMS, intracortical inhibitory and facilitatory circuit excitability was assessed by means of a paired pulse paradigm (conditioning stimulus 80% MT and test stimulus 120% MT) with two different interstimulus intervals: 2 ms (inhibitory) and 10 ms (facilitatory). Amplitude of the responses was expressed as the percentage of motor evoked potential (MEP) to test stimulus alone. Results showed that in basal condition migraineurs present significantly reduced levels of intracortical inhibition (ICI) compared to controls. More importantly, opposite results were obtained in migraineurs with respect to controls when 1 Hz rTMS was applied. Specifically, whereas intracortical facilitation (ICF) significantly decreased in controls, it significantly increased in migraineurs. ICI levels were not significantly affected by low-frequency stimulation. Our results showed that motor as well as sensory cortex of migraine patients present an abnormal modulation of cortical excitability, where a relevant role is likely played by the inefficiency of inhibitory circuits.