Induction of plasticity in the human motor cortex by paired associative stimulation.
Stefan K; Kunesch E; Cohen LG; Benecke R; Classen J
Brain 2000 Mar;123 Pt 3:572-84

Current Models Of Motor Cortical Plasticity, Developed In Studies
On Experimental Animals, Emphasize The Importance Of The
Conjoint Activity Of Somatosensory Afferents And Intrinsic Motor
Cortical Circuits. The Hypothesis That An Enduring Change In
Excitability In The Cortical Output Circuitry Can Be Induced In The
Human Motor Cortex By A Paired-stimulation Protocol Was Tested.
Low-frequency Median Nerve Stimulation Was Paired With
Transcranial Magnetic Stimulation (TMS) Over The Optimal
Cranial Site For Stimulating The Abductor Pollicis Brevis Muscle
(APB). This Protocol Induced An Increase In The Amplitudes Of
The Motor Evoked Potentials (MEPs) In The Resting APB As Well
As A Prolongation Of The Silent Period Measured In The
Precontracted APB Following TMS; Amplitudes Of MEPs
Measured In Voluntary Contraction Remained Unchanged.
Experiments Testing The Excitability Of Spinal Motoneurons Using
F-wave Studies And Electrical Stimulation Of The Brainstem
Suggested That The Site Of The Plastic Changes Was Within The
Motor Cortex. The Increases In Resting Amplitudes And Silent
Period Duration Were Conditionally Dependent On The Timing
Between The Afferent And The Magnetic Stimulation In That They
Were Present When Events Elicited By Afferent And Magnetic
Stimulation Were Synchronous At The Level Of The Motor Cortex.
Plasticity Induced By Paired Stimulation Evolved Rapidly (within
30 Min), Was Persistent (minimum Duration 30-60 Min) Yet
Reversible, And Was Topographically Specific. This Combination Of
Features And The Similarity To Properties Of Induced Enduring
Changes In Synaptic Efficacy, As Elucidated In Animal Studies,
Leads Us To Propose That The Induced Plasticity May Represent A
Signature Of Associative Long-term Potentiation Of Cortical
Synapses Or Closely Related Neuronal Mechanisms In The Human
Association Learning/*physiology
Motor Cortex/*physiology
Neuronal Plasticity/*physiology




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