Motor imagery of phasic thumb abduction temporally and spatially modulates corticospinal excitability

Objective: To explore the spatial and temporal characteristics of the modulation of corticospinal and segmental excitability during actual and imagined movement of a single digit. Methods: Using transcranial magnetic stimulation (TMS), motor evoked potentials (MEPs) were evoked in abductor pollicis brevis (APB) and abductor digiti minimi (ADM) of the dominant hand in 8 subjects, while they either rested, isometrically contracted their thenar muscles in time with a 1 Hz metronome, or imagined doing so. Magnetic stimuli were delivered during the ‘on’ and ‘off’ phases of the real and imagined movements. F waves were also recorded from APB and ADM under rest and motor imagery conditions. Results: It was found that both motor imagery and actual movement produced a muscle-specific, temporally modulated increase in corticospinal excitability during the task. The evidence of F-wave modulation was inconclusive. Conclusions: These results lend further support to the notion that actual movement and motor imagery modulate corticospinal excitability in a similar manner, primarily at the supraspinal level. Significance: Motor imagery and actual movement appear to modulate motor cortex excitability with a similar degree of spatial and temporal resolution, which supports the use of motor imagery in the rehabilitation of motor function.