Modulations of Use-Dependent Excitability Changes of Human Motor Cortex (M1) by Practice Condition

Effects of repetitive index finger abductions on excitability changes in the human primary motor cortex (M1) are assumed to be dependent on practice conditions of the task. To address how different effects occur dependent on various practice conditions, motor evoked potentials (MEPs) elicited from the first dorsal interosseous (FDI) muscle were investigated. Practice effects on the index finger abduction were examined for changes in excitability of first dorsal interosseous muscle under three forearm position changes (neutral vs prone) and two muscle contraction modes (isometric vs isotonic). Analysis showed that after practice MEP amplitude increased in the prone position but not in the neutral position and MEP increases in the isotonic contraction were larger than those in the isometric mode. These results suggest that use-dependent excitability changes are largely dependent on practice conditions because the amount of afferent input depends on the practice conditions.