title: Induction of Long-term Depression-like Plasticity by Pairings of Motor Imagination and Peripheral Electrical Stimulation.
abstract: Long-term depression (LTD) and long-term potentiation (LTP)-like plasticity are models of synaptic plasticity which have been associated with memory and learning. The induction of LTD and LTP-like plasticity, using different stimulation protocols, has been proposed as a means of addressing abnormalities in cortical excitability associated with conditions such as focal hand dystonia and stroke. The aim of this study was to investigate whether the excitability of the cortical projections to the tibialis anterior (TA) muscle could be decreased when dorsiflexion of the ankle joint was imagined and paired with peripheral electrical stimulation (ES) of the nerve supplying the antagonist soleus muscle. The effect of stimulus timing was evaluated by comparing paired stimulation timed to reach the cortex before, at and after the onset of imagined movement. Fourteen healthy subjects participated in six experimental sessions held on non-consecutive days. The timing of stimulation delivery was determined oﬄine based on the contingent negative variation (CNV) of electroencephalography brain data obtained during imagined dorsiflexion. Afferent stimulation was provided via a single pulse ES to the peripheral nerve paired, based on the CNV, with motor imagination of ankle dorsiflexion. A significant decrease (P = 0.001) in the excitability of the cortical projection of TA was observed when the afferent volley from the ES of the tibial nerve (TN) reached the cortex at the onset of motor imagination based on the CNV. When TN stimulation was delivered before (P = 0.62), or after (P = 0.23) imagined movement onset there was no significant effect. Nor was a significant effect found when ES of the TN was applied independent of imagined movement (P = 0.45). Therefore, the excitability of the cortical projection to a muscle can be inhibited when ES of the nerve supplying the antagonist muscle is precisely paired with the onset of imagined movement.
authors.affiliation: Center for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University Denmark Aalborg, Denmark.
authors.forename: Mads
authors.initials: M
authors.lastname: Jochumsen
authors.affiliation: Health and Rehabilitation Research Institute, Auckland University of Technology Auckland, New Zealand.
authors.forename: Nada
authors.initials: N
authors.lastname: Signal
authors.affiliation: Center for Chiropractic Research, New Zealand College of Chiropractic Auckland, New Zealand.
authors.forename: Rasmus W
authors.initials: RW
authors.lastname: Nedergaard
authors.affiliation: Health and Rehabilitation Research Institute, Auckland University of Technology Auckland, New Zealand.
authors.forename: Denise
authors.initials: D
authors.lastname: Taylor
authors.affiliation: Center for Chiropractic Research, New Zealand College of Chiropractic Auckland, New Zealand.
authors.forename: Heidi
authors.initials: H
authors.lastname: Haavik
authors.affiliation: Center for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University Denmark Aalborg, Denmark ; Health and Rehabilitation Research Institute, Auckland University of Technology Auckland, New Zealand ; Center for Chiropractic Research, New Zealand College of Chiropractic Auckland, New Zealand.
authors.forename: Imran K
authors.initials: IK
authors.lastname: Niazi
keywords: associative stimulation; brain plasticity; contingent negative variation; cortical excitability; long-term depression; long-term potentiation; motor imagination