Combined action observation and imagery facilitates corticospinal excitability

Abstract

Observation and imagery of movement both activate similar brain regions to those involved in movement execution. As such, both are recommended as techniques for aiding the recovery of motor function following stroke. Traditionally, action observation and movement imagery (MI) have been considered as independent intervention techniques. Researchers have however begun to consider the possibility of combining the two techniques into a single intervention strategy. This study investigated the effect of combined action observation and MI on corticospinal excitability, in comparison to either observation or imagery alone. Single-pulse transcranial magnetic stimulation (TMS) was delivered to the hand representation of the left motor cortex during combined action observation and MI, passive observation (PO), or MI of right index finger abduction-adduction movements or control conditions. Motor evoked potentials (MEPs) were recorded from the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles of the right hand. The combined action observation and MI condition produced MEPs of larger amplitude than were obtained during PO and control conditions. This effect was only present in the FDI muscle, indicating the facilitation of corticospinal excitability during the combined condition was specific to the muscles involved in the observed/imagined task. These findings have implications for stroke rehabilitation, where combined action observation and MI interventions may prove to be more effective than observation or imagery alone.

Keywords: action observation; motor evoked potentials; movement imagery; stroke rehabilitation; transcranial magnetic stimulation.

Figure 1

A schematic representation of the six conditions in the experiment. All videos were 9000 ms duration and one stimulation was delivered per trial at either 3500 or 8000 ms. An auditory metronome was present during the Backward Counting (BC) and Movement Imagery (MI) conditions.

Figure 2

Mean MEP amplitudes, displayed as z-scores, recorded from all six conditions for (A) the right FDI muscle and (B) the right ADM muscle. Asterisks indicate significant differences between conditions.