Effects of action observation on physical training after stroke

Abstract

Background and purpose: In healthy humans, observation of another individual performing a motor training task (action observation [AO]) facilitates, in the observer, the effects of physical training (PT) on motor memory formation. It is not known whether this facilitatory process, of potential value for neurorehabilitation, occurs after stroke.

Methods: Eight chronic stroke patients completed this crossover-randomized investigation. A transcranial magnetic stimulation protocol that tests formation of motor memories was used to determine the effects of PT alone and in combination with AO in 2 different forms: congruent (PT+AO(congruent)) and incongruent (PT+AO(incongruent)) to the practiced task.

Results: The magnitude of motor memory formation was larger with PT+AO(congruent) than with PT alone or PT+AO(incongruent). This effect was associated with a differential corticomotor excitability change in the muscles acting as agonist and antagonist of the trained/observed movements.

Conclusions: These results indicate that congruent AO in association with physical training can enhance the effects of motor training after stroke.

Fig. 1

Graphic representation of the experimental set up. a) Baseline. Black lines depict the direction of individual TMS-evoked thumb movements, in this example a combination of flexion and abduction. b) Interventions. Patients perform: (1) physical training (PT) alone (represented by a drawing of a thumb and black lines showing the direction of the practice movements), (2) PT+AO_INCONGRUENT (same drawing as in PT plus a still picture obtained from the video presented during the experiments showing the thumb in flexion position and black lines depicting the observed movements direction, opposite to the physically trained motions), and (3) PT+AO_CONGRUENT (shown by the same drawing as in PT plus a still picture with the thumb in extension position and black lines depicting the direction of the observed movements). In the 3 experimental sessions, the physical training component consisted of thumb movements practiced in a direction opposite to the baseline TMS-evoked movement direction (in the sketch this is represented by the TTZ, a training target zone defined as a window of ± 20° centered on the mean training direction. c) Post-intervention. The percent of TMS-evoked thumb movements falling within the TTZ, the primary outcome measure, was calculated.

Fig 2

Percent of intervention-dependent TMS-evoked thumb movements falling in the TTZ (bar graph, n=8; mean ± SEM). Note the increase in the percentage of TMS-evoked thumb movements falling in the TTZ when MT+AO_CONGRUENT is performed. *, p< 0.02. In light gray, the percent of movements in TTZ for each subject is shown. Seven of eight subjects experience an increased in TMS-evoked motions following the trained and observed directions in the PT+AO_CONGRUENT condition.

Fig. 3

Corticomotor excitability changes as measured by motor evoked potential amplitudes (MEP). In 3a, absolute MEP amplitudes for the agonist and antagonist muscles to the physically practice direction is shown at baseline (pre) and after (post) each intervention in the 3 sessions. After PT alone MEP amplitude decreased similarly for both muscles and have minimal changes after PT+AO_INCONGRUENT. In the PT+AO_CONGRUENT condition, MEP amplitude for the agonist muscle had a slight increased whereas the antagonist muscle decreased. This differential modulation of excitability is evidenced in the MEP_{POST-/PRE- INTERVENTION} ratio (3b). Here, only PT+AO_CONGRUENT elicited a significant different ratio. *, p< 0.03.