title: Effects of visual cortex activation on the nociceptive blink reflex in healthy subjects.
abstract: Bright light can cause excessive visual discomfort, referred to as photophobia. The precise mechanisms linking luminance to the trigeminal nociceptive system supposed to mediate this discomfort are not known. To address this issue in healthy human subjects we modulated differentially visual cortex activity by repetitive transcranial magnetic stimulation (rTMS) or flash light stimulation, and studied the effect on supraorbital pain thresholds and the nociceptive-specific blink reflex (nBR). Low frequency rTMS that inhibits the underlying cortex, significantly decreased pain thresholds, increased the 1st nBR block ipsi- and contralaterally and potentiated habituation contralaterally. After high frequency or sham rTMS over the visual cortex, and rMS over the right greater occipital nerve we found no significant change. By contrast, excitatory flash light stimulation increased pain thresholds, decreased the 1st nBR block of ipsi- and contralaterally and increased habituation contralaterally. Our data demonstrate in healthy subjects a functional relation between the visual cortex and the trigeminal nociceptive system, as assessed by the nociceptive blink reflex. The results argue in favour of a top-down inhibitory pathway from the visual areas to trigemino-cervical nociceptors. We postulate that in normal conditions this visuo-trigeminal inhibitory pathway may avoid disturbance of vision by too frequent blinking and that hypoactivity of the visual cortex for pathological reasons may promote headache and photophobia.
authors.affiliation: Headache Research Unit, University Department of Neurology, Liège University, Liège, Belgium.
authors.forename: Simona L
authors.initials: SL
authors.lastname: Sava
authors.affiliation: Headache Research Unit, University Department of Neurology, Liège University, Liège, Belgium.
authors.forename: Victor
authors.initials: V
authors.lastname: de Pasqua
authors.forename: Delphine
authors.initials: D
authors.lastname: Magis
authors.affiliation: Headache Research Unit, University Department of Neurology, Liège University, Liège, Belgium.
authors.forename: Delphine
authors.initials: D
authors.lastname: Magis
authors.forename: Jean
authors.initials: J
authors.lastname: Schoenen
authors.affiliation: Headache Research Unit, University Department of Neurology, Liège University, Liège, Belgium.
authors.forename: Jean
authors.initials: J
authors.lastname: Schoenen
mesh_terms: D000328:Adult; D001767:Blinking / Q000502:physiology*; D016022:Case-Control Studies; D005260:Female; D005500:Follow-Up Studies; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D009619:Nociceptors / Q000502:physiology*; D011379:Prognosis; D012018:Reflex / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D014793:Visual Cortex / Q000502:physiology*