Facilitation of corticospinal excitability according to motor imagery and mirror therapy in healthy subjects and stroke patients

Abstract

Objective: To delineate the changes in corticospinal excitability when individuals are asked to exercise their hand using observation, motor imagery, voluntary exercise, and exercise with a mirror.

Method: The participants consisted of 30 healthy subjects and 30 stroke patients. In healthy subjects, the amplitudes and latencies of motor evoked potential (MEP) were obtained using seven conditions: (A) rest; (B) imagery; (C) observation and imagery of the hand activity of other individuals; (D) observation and imagery of own ipsilateral hand activity; (E) observation and imagery of the hand activity of another individual with a mirror; (F) observation and imagery of own symmetric ipsilateral hand activity (thumb abduction) with a mirror; and (G) observation and imagery of own asymmetric ipsilateral hand activity (little finger abduction) with a mirror. In stroke patients, MEPs were obtained in the A, C, D, E, F conditions.

Results: In both groups, increment of the percentage MEP amplitude (at rest) and latency decrement of MEPs were significantly higher during the observation of the activity of the hand of another individual with a mirror and during symmetric ipsilateral hand activity on their own hand with a mirror than they were without a mirror. In healthy subjects, the increment of percentage MEP amplitude and latency decrement were significantly higher during the observation of the symmetric ipsilateral hand activity with a mirror compared to the observation of the activity of the asymmetric ipsilateral hand with a mirror of their own hand.

Conclusion: In both groups, corticospinal excitability was facilitated by viewing the mirror image of the activity of the ipsilateral hand. These findings provide neurophysiological evidence supporting the application of various mirror imagery programs during stroke rehabilitation.

Keywords: Corticospinal excitability; Mirror therapy; Motor imagery; Stroke; Transcranial magnetic stimulation.

Fig. 1

(A, B) Relaxation and kinesthetic motor imagery state. (C) Observation and imagery of the activity of the hand of another individual without a mirror. (D) Observation and imagery of own hand activity without a mirror. (E) Observation and imagery of the activity of the hand of another individual with a mirror. (F) Observation and imagery of own symmetric hand activity with a mirror. (G) Observation and imagery of own asymmetric hand activity with a mirror.

Fig. 2

Increment of percentage MEP values in healthy subjects. Mean (±SEM) values of the MEP amplitude measured during the experiment, expressed as percentage of the MEP at rest in 30 healthy subjects. Based on repeated measures ANOVA, the percentage MEP amplitude of observation and imagery of the activity of the hand of another individual with a mirror (E) was significantly increased compared with observation and imagery of the activity of the hand of another individual without a mirror (C) (^†p<0.01). In addition, the percentage MEP amplitude of observation and imagery of self hand activity with a mirror (F) was significantly increased compared with observation and imagery of own hand activity without a mirror (D) (^*p<0.05). (A) rest; (B) imagery; (C) observation and imagery of the activity of the hand of another individual without a mirror; (D) observation and imagery of self hand activity without a mirror; (E) observation and imagery of the activity of the hand of another individual with a mirror; (F) observation and imagery of own symmetric hand activity with a mirror; and (G) observation and imagery of own asymmetric hand activity with a mirror.

Fig. 3

Decrement of MEP latency values in healthy subjects. Mean (±SEM) values of the MEP latency during the experiment in 30 healthy subjects. Based on repeated measures ANOVA, the MEP latency of observation and imagery of the activity of the hand of another individual with a mirror (E) was significantly decreased compared with observation and imagery of the activity of the hand of another individual without a mirror (C) (^‡p<0.001). In addition, the MEP latency of observation and imagery of own hand activity with a mirror (F) was significantly decreased compared with observation and imagery of own hand activity without a mirror (D) (^†p<0.01). (A) rest; (B) imagery; (C) observation and imagery of the activity of the hand of another individual without a mirror; (D) observation and imagery of own hand activity without a mirror; (E) observation and imagery of the activity of the hand of another individual with a mirror; (F) observation and imagery of own symmetric hand activity with a mirror; and (G) observation and imagery of own asymmetric hand activity with a mirror.

Fig. 4

Observation-execution matching. The percentage MEP amplitude increment and latency decrement of observation and imagery of own symmetric hand activity with a mirror (F) was significantly increased compared with observation and imagery of own asymmetric hand activity with a mirror (G) (^‡p<0.001) in 30 healthy subjects (observation-execution matching).

Fig. 5

Increment of percentage MEP amplitude and decrement of MEP latency in stroke patients. The percentage MEP amplitude increment and latency decrement of MEPs were significantly greater in the activity of the hand of another individual with a mirror (E) than in observation and imagery of the activity of the hand of another individual without a mirror (C) (^‡p<0.001). In addition, the percentage MEP amplitude increment and latency decrement of MEPs were significantly greater in own hand activity with a mirror (F) than in observation and imagery of own hand activity without a mirror (D) (^†p<0.01, ^‡p<0.001). (A) rest; (C) observation and imagery of the activity of the hand of another individual without a mirror; (D) observation and imagery of self hand activity without a mirror; (E) observation and imagery of the activity of the hand of another individual with a mirror; (F) observation and imagery of the own hand activity with a mirror.