title: Cerebellar modulation of human associative plasticity.
abstract: Paired associative stimulation (PAS) is a method commonly used in human studies of motor cortex synaptic plasticity. It involves repeated pairs of electrical stimuli to the median nerve and transcranial magnetic stimulation (TMS) of the motor cortex. If the interval between peripheral and TMS stimulation is around 21–25 ms, corticospinal excitability is increased for the following 30–60 min via a long term potentiation (LTP)-like effect within the primary motor cortex. Previous work has shown that PAS depends on the present and previous levels of activity in cortex, and that it can be modified by motor learning or attention. Here we show that simultaneous transcranial direct current stimulation (TDCS; 2 mA) over the cerebellum can abolish the PAS effect entirely. Surprisingly, the effect is seen when the PAS interval is 25 ms but not when it is 21.5 ms. There are two implications from this work. First, the cerebellum influences PAS effects in motor cortex; second, LTP-like effects of PAS have at least two different mechanisms. The results are relevant for interpretation of pathological changes that have been reported in response to PAS in people with movement disorders and to changes in healthy individuals following exercise or other interventions.
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, Queen Square, London WC1N 3BG, UK. mhamada-tky@umin.net
authors.forename: Masashi
authors.initials: M
authors.lastname: Hamada
authors.forename: Gionata
authors.initials: G
authors.lastname: Strigaro
authors.forename: Nagako
authors.initials: N
authors.lastname: Murase
authors.forename: Anna
authors.initials: A
authors.lastname: Sadnicka
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Galea
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Edwards
authors.forename: John C
authors.initials: JC
authors.lastname: Rothwell
mesh_terms: D000328:Adult; D002531:Cerebellum / Q000502:physiology*; D018592:Cross-Over Studies; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D017774:Long-Term Potentiation; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult