title: Increased variability of motor cortical excitability to transcranial magnetic stimulation in migraine: a new clue to an old enigma.
abstract: Increased, decreased or normal excitability to transcranial magnetic stimulation (TMS) has been reported in the motor (M1) and visual cortices of patients with migraine. Light deprivation (LD) has been reported to modulate M1 excitability in control subjects (CS). Still, effects of LD on M1 excitability compared to exposure to environmental light exposure (EL) had not been previously described in patients with migraine (MP). To further our knowledge about differences between CS and MP, regarding M1 excitability and effects of LD on M1 excitability, we opted for a novel approach by extending measurement conditions. We measured motor thresholds (MTs) to TMS, short-interval intracortical inhibition, and ratios between motor-evoked potential amplitudes and supramaximal M responses in MP and CS on two different days, before and after LD or EL. Motor thresholds significantly increased in MP in LD and EL sessions, and remained stable in CS. There were no significant between-group differences in other measures of TMS. Short-term variation of MTs was greater in MP compared to CS. Fluctuation in excitability over hours or days in MP is an issue that, until now, has been relatively neglected. The results presented here will help to reconcile conflicting observations.
authors: Instituto Israelita de Ensino e Pesquisa, Hospital Israelita Albert Einstein, Av. Albert Einstein, 627/2SS, Morumbi, São Paulo, SP, 05652-900, Brazil. adriana.conforto@gmail.com
authors: Adriana B
authors: AB
authors: Conforto
authors: Mariana S
authors: MS
authors: Moraes
authors: Edson
authors: E
authors: Amaro
authors: William B
authors: WB
authors: Young
authors: Lais A
authors: LA
authors: Lois
authors: André L
authors: AL
authors: Gonçalves
authors: Mario F P
authors: MF
authors: Peres
mesh_terms: D000328:Adult; D018592:Cross-Over Studies; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008881:Migraine Disorders / Q000503:physiopathology*; D009044:Motor Cortex / Q000503:physiopathology*; D010775:Photic Stimulation; D050781:Transcranial Magnetic Stimulation