METHODS: In two randomised, double-blinded, cross-over or placebo-controlled (caffeine) studies, we measured sixty subjects in eight sessions (n = 30, Male: Female = 1:1 in each study).
RESULTS: We found caffeine increased motor cortex excitability in caffeine naïve subjects. The aftereffects in caffeine naïve subjects were enhanced and prolonged when combined with PAS 25. Caffeine also increased alertness and the motor evoked potentials (MEPs) were reduced under light deprivation in caffeine consumers both with and without caffeine. In caffeine consumers, the time of day had no effect on tACS-induced plasticity.
CONCLUSIONS: We conclude that caffeine should be avoided or controlled as confounding factor for brain stimulation protocols. It is also important to keep the brightness constant in all sessions and study groups should not be mixed with caffeine-naïve and caffeine consuming participants.
SIGNIFICANCE: Caffeine is one of the confounding factors in the plasticity induction studies and it induces different excitability effects in caffeine-naïve and caffeine-adapted subjects. This study was registered in the ClinicalTrials.gov with these registration IDs: 1) NCT03720665 https://clinicaltrials.gov/ct2/results?cond=NCT03720665&term=&cntry=&state=&city=&dist= 2) NCT04011670 https://clinicaltrials.gov/ct2/results?cond=&term=NCT04011670&cntry=&state=&city=&dist=.
DESIGN: In this repeated-measures study, 20 normally hearing adults aged between 18 and 30 years were recruited. Tone bursts (500, 1000, 2000, and 4000 Hz) were used to record PAMR thresholds at 3 different stimulus repetition rates (6.1/s, 11.1/s, and 17.1/s).
RESULTS: Statistically higher PAMR thresholds were found for the faster stimulus rate (17.1/s) compared with the slower stimulus rate (6.1/s) (p < 0.05). For all stimulus rates and frequencies, significant correlations were found between PAMR and pure-tone audiometry thresholds (r = 0.62 to 0.82).
CONCLUSIONS: Even though the stimulus rate effect was significant at most of the tested frequencies, the differences in PAMR thresholds between the rates were small (<5 dB). Nevertheless, based on the correlation results, we suggest the use of 11.1/s stimulus rate when recording PAMR thresholds.
METHODS: Serial nerve conduction studies (NCS) were retrospectively analyzed in 82 GBS patients from 3 centers. The criteria for the presence of ERCF in a nerve were: (i) a 50% increase in amplitude of distal compound muscle action potentials or sensory nerve action potentials; or (ii) resolution of proximal motor conduction block with an accompanying decrease in distal latencies or compound muscle action potential duration or increase in conduction velocities.
RESULTS: Of 82 patients from 3 centers, 37 (45%) had ERCF, 21 (26%) had a contrasting evolution pattern, and 8 (10%) had both. Sixteen patients did not show an amplitude increase of at least 50%.
CONCLUSION: Our proposed criteria identified a group of patients with a characteristic evolution of NCS abnormality that is consistent with ERCF. Muscle Nerve 56: 919-924, 2017.