A temporally asymmetric Hebbian rule governing plasticity in the XXXX motor cortex.

@entity1 @entity308 @entity1024 @entity9808 @entity14031 @entity3931 @entity460
Synaptic plasticity is conspicuously dependent on the temporal order of the pre- and postsynaptic activity. @entity1 motor cortical excitability can be increased by a paired associative stimulation (PAS) protocol. Here we show that it can also be decreased by minimally changing the interval between the two associative stimuli. Corticomotor excitability of the abductor pollicis brevis (APB) representation was tested before and after repetitively pairing of single right median nerve simulation with single pulse @entity9808 ( @entity9808 ) delivered over the optimal site for activation of the contralateral APB. Following PAS, @entity308 of @entity9808 -evoked motor-evoked potentials (MEPs) was induced only when the median nerve stimulation preceded the @entity9808 pulse by 10 ms, while enhancement of cortical excitability was induced using an interstimulus interval of 25 ms, suggesting an important role of the sequence of cortical events triggered by the two stimulation modalities. Experiments using F-wave studies and electrical brain stem stimulation indicated that the site of the plastic changes underlying the decrease of MEP amplitudes following PAS (10 ms) was within the motor cortex. MEP amplitudes remained @entity308 for approximately 90 min. The decrease of MEP amplitudes was blocked when PAS(10 ms) was performed under the influence of @entity14031 , an @entity1024 -receptor antagonist, or @entity3931 , an L-type voltage-gated @entity460 -channel antagonist. The physiological profile of the @entity308 of @entity1 motor cortical excitability following PAS(10 ms) suggests long-term @entity308 of synaptic efficacy to be involved. Together with earlier findings, this study suggests that strict temporal Hebbian rules govern the induction of long-term potentiation/long-term @entity308 -like phenomena in vivo in the @entity1 primary motor cortex.
