title: Associative plasticity in surround inhibition circuits in human motor cortex.
abstract: Surround inhibition is a physiological mechanism that is hypothesised to improve contrast between signals in the central nervous system. In the human motor system, motor surround inhibition (mSI) can be assessed using transcranial magnetic stimulation (TMS). We evaluated whether it is possible to modulate mSI, using a paradigm able to induce plastic effects in primary motor cortex (M1). Fifteen healthy volunteers participated in the experiments. To assess mSI, we delivered single pulses at rest and at the onset of a right thumb abduction. TMS pulses over abductor digiti minimi (ADM; surround muscle) hotspot were delivered when EMG activity in right abductor pollicis brevis (APB; active muscle) > 100 μV was detected. Paired associative stimulation (PAS) was delivered using peripheral median nerve electric stimulation and TMS over APB M1 area at an interstimulus interval of 21.5 ms for the real PAS (PAS21.5) and 100 ms for the sham PAS (PAS100). To verify the effect of PAS21.5 on mSI we collected 20 MEPs from ADM at rest and during APB movements before (T0) and 5 (T1), 15 (T2) and 30 (T3) minutes after PAS21.5. mSI from APB to ADM was present at baseline. PAS21.5 increased the amount of mSI compared with baseline whereas there was no effect after PAS100. Our results suggest that mSI is an adaptable phenomenon depending on prior experience.
authors.affiliation: Neuromed Institute IRCCS, Via Atinense 18, 86077, Pozzilli, IS, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Belvisi
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Kassavetis
authors.forename: Matteo
authors.initials: M
authors.lastname: Bologna
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Edwards
authors.forename: Alfredo
authors.initials: A
authors.lastname: Berardelli
authors.forename: John C
authors.initials: JC
authors.lastname: Rothwell
mesh_terms: D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D012146:Rest; D013933:Thumb / Q000502:physiology; D050781:Transcranial Magnetic Stimulation
keywords: cortical plasticity; motor control; movement; neurophysiology; transcranial magnetic stimulation