title: Does caffeine modify corticomotor excitability?
abstract: OBJECTIVE
  To test the influence of caffeine on the lower and upper motor neuron excitability.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  In our investigation, caffeine elicited a consistent decrease of the CSP, suggesting that caffeine increases cortical neuronal excitability.
authors.affiliation: Dementia Group, Institute of Molecular Medicine, Faculty of Medicine of Lisbon and Hospital de Santa Maria, Portugal.
authors.forename: V
authors.initials: V
authors.lastname: Cerqueira
authors.forename: A
authors.initials: A
authors.lastname: de Mendonça
authors.forename: A
authors.initials: A
authors.lastname: Minez
authors.forename: A R
authors.initials: AR
authors.lastname: Dias
authors.forename: M
authors.initials: M
authors.lastname: de Carvalho
mesh_terms: D000328:Adult; D002110:Caffeine / Q000097:blood / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000097:blood / Q000494:pharmacology*; D004311:Double-Blind Method; D004569:Electroencephalography / Q000187:drug effects; D004574:Electromagnetic Fields; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000187:drug effects*; D009046:Motor Neurons / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D010525:Peripheral Nerves / Q000187:drug effects / Q000502:physiology; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects; D013268:Stimulation, Chemical; D050781:Transcranial Magnetic Stimulation
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine