Afferent stimulation facilitates performance on a novel motor task

Training on a motor task results in performance improvements that are accompanied by increases in motor cortex excitability. Moreover, periods of afferent stimulation result in increased motor cortex excitability. There is increasing evidence to suggest that raised motor cortical excitability may facilitate movement and learning. Here we examined whether a period of electrical stimulation of hand afferents ("associative stimulation"), known to increase motor cortex excitability, facilitated the performance of a complex sensorimotor task. Three groups of nine normal subjects participated in these studies. All subjects were trained on the grooved pegboard test (GPT). Training consisted of three blocks, each of five trials, of placing pegs as quickly as possible. The time to complete each block was recorded. One group of subjects had a 1-h period of associative stimulation prior to training on the GPT. A second group received non-associative stimulation (which does not change cortical excitability) of the same hand afferents while a third group received no stimulation prior to training. Motor evoked potentials (MEPs) were recorded from the first dorsal interosseous (FDI) and abductor digiti minimus (ADM) muscles both prior to and following stimulation and performance of the GPT. In contrast to non-associative stimulation, associative stimulation increased motor cortical excitability, as evidenced by an increase in the amplitude of MEPs evoked in the FDI, one of the stimulated muscles, but not the ADM. Training on the GPT resulted in significant improvements in the time taken to complete the task for all three groups. However, in subjects who had preconditioning associative stimulation, performance on the GPT improved more rapidly. Additionally, there was a strong trend for the improvement in the performance of the stimulated group to be greater than that of the control group. The results of the present study suggest that increased motor cortical excitability, induced by associative stimulation, may facilitate the performance of a novel complex sensorimotor task.