title: Task-dependent changes in late inhibitory and disinhibitory actions within the primary motor cortex in humans.
abstract: The objective of the present study was to investigate the time course of long-interval intracortical inhibition (LICI) and late cortical disinhibition (LCD) as a function of the motor task (index abduction, thumb-index precision grip). Motor-evoked potentials were recorded from the first dorsal interosseus (FDI) muscle of the dominant limb in 13 healthy subjects. We used paired-pulse transcranial magnetic stimulation (TMS) paradigms in which a test pulse was preceded by a suprathreshold priming pulse (130% of the resting motor threshold) with varying interstimulus intervals (ISIs). In each task, double pulses were delivered with ISIs ranging from 30% of the corresponding silent period (SP; ~ 45 ms) to 220% of the SP (~ 330 ms). In both tasks, we found that LICI was followed by LCD (namely a period of increased cortical excitability lasting until ~ 200% of the SP). The time-dependent modulation of LICI and LCD differed in the two tasks; LICI was shorter (i.e. disinhibition occurred earlier) and LCD was more intense during precision grip than during index abduction. Long-interval intracortical inhibition disappeared well before the end of the SP in the precision grip task, suggesting that the mechanisms underlying these two inhibitory phenomena are distinct. Our data suggest that disinhibition might reflect adaptation of neural circuit excitability to the functional requirements of the motor task.
authors: Lille-Nord de France University, Department of Clinical Neurophysiology, EA 4559, Lille University Hospital, Lille Cedex, France.
authors: Alexandre
authors: A
authors: Caux-Dedeystère
authors: Mélanie
authors: M
authors: Rambour
authors: Alain
authors: A
authors: Duhamel
authors: François
authors: F
authors: Cassim
authors: Philippe
authors: P
authors: Derambure
authors: Hervé
authors: H
authors: Devanne
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: disinhibition; index abduction; motor control; precision grip; transcranial magnetic stimulation