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

Abstract

To explore the spatial and temporal characteristics of the modulation of corticospinal and segmental excitability during actual and imagined movement of a single digit. 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. 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. 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. 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.