Does caffeine modify corticomotor excitability?

To test the influence of caffeine on the lower and upper motor neuron excitability. In Experiment A, 18 healthy subjects received 200 mg of caffeine or placebo, in a randomized, double-blind, placebo-controlled design protocol. Mean F-waves amplitude, amplitude of the motor response evoked by magnetic stimulation (MEP), MEP duration, cortical silent period (CSP), central conduction time, and cortical threshold were evaluated. In Experiment B, 6 healthy controls received 400 mg of caffeine, the peripheral silent period (PSP) and CSP were evaluated. CSP was recorded bilaterally in biceps brachii (intensity 10% above threshold) and abductor digiti minimi (ADM) (intensity at 10% and 50% above threshold). Muscle contraction was above 50% of the maximum force in both experiments. Latencies were defined by a technician who was not aware of this investigation. Serum caffeine level was evaluated. In Experiment A, only the CSP, recorded in both ADM with intensity at 10% above threshold showed a significant change after caffeine (decrease of 17.1 ± 34.0 ms, about 12% reduction). In Experiment B, PSP did not change, but CSP tested with intensities 10% above threshold was significantly decreased by 20.8 ± 34.4 ms in ADM and 13.5 ± 13.8 ms in biceps (about 13 and 16%, respectively). Serum caffeine level clearly increased after consumption but no correlation could be found between these levels and CSP reduction. In our investigation, caffeine elicited a consistent decrease of the CSP, suggesting that caffeine increases cortical neuronal excitability. Évaluer l'influence de la caféine sur l'excitabilité des motoneurones inférieurs et supérieurs. Dans l'expérience A, 18 sujets en bonne santé ont reçu 200 mg de caféine ou un placebo, selon un protocole aléatoire et en double insu. Ont été mesurés : l'amplitude moyenne des ondes F, l'amplitude du potentiel évoqué moteur (PEM) obtenu par stimulation magnétique corticale, la durée du PEM, la période de silence cortical (PSC), le temps de conduction centrale et le seuil moteur cortical. Dans l'expérience B, six sujets témoins en bonne santé on reçu 400 mg de caféine et nous avons évalué la période de silence périphérique (PSP) et la PSC. La PSC a été enregistrée bilatéralement dans les biceps (intensité 10 % supérieure au seuil moteur) et les abducteurs du cinquième doigt (ADM) (intensités à 10 % et 50 % au-dessus du seuil). Les contractions musculaires étaient supérieures à 50 % de la force maximale dans les deux expériences.