Abstract
Excitability of the corticospinal pathway increases during observation of an action. However, how corticospinal excitability changes during observation of sequential actions in the course of acquiring novel skills (observational learning) remains unexplored. To investigate this, we used a previously unpracticed sequence of ten hand postures. Participants were asked to repeat observation and replication of the sequence. This block of observation and replication was repeated 5 times. During observation of a given hand posture (OK sign), motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation were recorded from hand muscles. In experiment 1, the OK sign appeared in the 9th position of the sequence. Almost all participants could replicate the OK sign only at the 5th block of the experiment. MEP amplitude was greater than that in the control, and decreased with the stages. This suggested that during observational learning of sequential hand postures MEP changed with the progress of the learning. To evaluate this idea, we performed two additional experiments. In experiment 2, the OK sign appeared in the 2nd position. Almost all participants replicated the OK sign even in the 1st block. The MEP amplitude did not change across stages. In experiment 3, the OK sign appeared in the 9th position, but the order of other signs was randomized in every stage. Many participants were not able to replicate the OK sign even during the 5th block of the experiment. The MEP amplitude did not change across stages. These results suggest that: (1) During observational learning modulation of corticospinal excitability is associated with the learning process. (2) Corticospinal excitability decreases as learning progresses.
Highlights
Most motor skills are acquired through physical practice, it is generally believed that observing an action performed by others is important in the improvement of the observer’s motor skills [1]
In the experiment 1, we investigated the modulation of motor-evoked potentials (MEPs) amplitude during observation of the OK sign
Recordings The electromyographic responses (EMG) were recorded from the left first dorsal interosseous (FDI), opponens pollicis (OP) and the abductor digiti minimi (ADM) muscles with disposable AgAgCl electrodes placed over the belly of muscles
Summary
Most motor skills are acquired through physical practice, it is generally believed that observing an action performed by others is important in the improvement of the observer’s motor skills [1]. There is behavioral evidence that observation of movements alone improves specific motor performance indices, such as reaction time, movement direction and movement trajectory [3,4,5,6]. The behavioral improvements follow excitability changes in the motor systems of the brain. Observation of an action modulates excitability of the corticospinal pathway, as was investigated by measuring the motor-evoked potential (MEP) to stimulation of the primary motor cortex using transcranial magnetic stimulation (TMS). Fadiga et al [7] showed that when humans observed a grasping action performed by others, the MEP of the hand muscles increased. The increases in MEP were largely specific to the muscles involved in the observed action [7,8,9,10]. Visual information is processed and forwarded in such a way that it can alter signals in the motor pathways that control movement
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