The European journal of neuroscience
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Although synaptic plasticity in the human cerebral cortex is governed by metaplasticity, whether a similar mechanism operates at brainstem level is unknown. In this study in healthy humans we examined the effects and interactions induced by pairing supraorbital nerve high-frequency electrical stimulation (HFS) protocols on the R2 component of the trigeminal blink reflex [Mao, J. B. & Evinger, C (2001) J Neurosci., 21:RC151(1-4)]. ⋯ When two CONTROL-HFS sessions were paired, the test CONTROL-HFS increased the latency and markedly reduced the duration and area of the R2 component. The analysis of the normalized data across the first three experimental sessions, corrected for the inhibitory effects found in the fourth experiment, showed that the test LTP-HFS potentiated the R2 component area of the trigeminal blink reflex only when preceded by a priming LTD-HFS. We propose that homosynaptic metaplasticity might operate in the brainstem circuitry of the blink reflex.
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We investigated whether conventional and diffusion tensor (DT) magnetic resonance imaging (MRI) features of the corticospinal tract (CST) contribute to the prediction of the long-term clinical evolution in patients with amyotrophic lateral sclerosis (ALS). Brain conventional and DT MRI were obtained from 18 healthy subjects and 24 patients with sporadic ALS. Mean diffusivity (MD) and fractional anisotropy (FA) of the CST were obtained. ⋯ Survival at year 3 was 42% in patients with CST FA ≤ 0.56 compared with 90% in patients with CST FA > 0.56. This study shows that more severe CST DT MRI abnormalities predict a poorer long-term clinical outcome in ALS patients. DT MRI of the brain has the potential to offer in vivo markers of disease severity.