THE chronometry of imagined and actual movements was investigated in a
patient with a unilateral lesion of the motor cortex. Motor imagery g
enerated highly accurate estimates of motor performance in a variety o
f situations, reflecting the hypokinesia of the contralesional hand. T
here were parallel increases in mental and actual movement times from
proximal to distal limb segments. Bimanual movements adopted the slowe
r speed of the impaired hand in both conditions. Imagined motor sequen
ces to the beat of a metronome predicted the maximum speed reached in
actual performance. Finally, visually guided pointing showed the same
target-size effects in the imagery and movement conditions. The result
s are in agreement with the hypothesis that common cerebral motor repr
esentations are activated when imaging and planning voluntary movement
s.