Does caffeine modify corticomotor excitability?
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.
Cerqueira
V
V
Dementia Group, Institute of Molecular Medicine, Faculty of Medicine of Lisbon and Hospital de Santa Maria, Portugal.
de Mendonça
A
A
Minez
A
A
Dias
A R
AR
de Carvalho
M
M
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
D000697:Central Nervous System Stimulants; D002110:Caffeine