Modulating the motor system by action observation after stroke

Abstract

Background and purpose: Much recent interest surrounds the use of action observation, which is observing another individual performing a motor task, in stroke rehabilitation, to promote motor recovery by engaging similar brain regions to action execution. This may be especially useful in individuals with limited mobility. Here, we assess how cortical motor activity during action observation is affected by stroke and by stroke-related motor deficits.

Methods: We used functional MRI to compare brain activity during right and left hand action observation in right-handed nondisabled participants and participants who were right-handed before left hemisphere stroke. All participants performed the same actions after their functional MRI.

Results: Nondisabled participants show greater bilateral cortical motor activity when observing actions made using the left hand, whereas participants with stroke show greater ipsilesional cortical motor activity when observing actions made using the right (paretic) hand (P<0.05; corrected). For both groups, action processing is modulated by motor capability: cortical motor activity is greater when observing the hand with lower motor scores (P<0.05; corrected). Furthermore, for stroke, the extent of ipsilesional activity correlates with lesion volume (P=0.049), in a pattern that suggests adaptive plasticity.

Conclusions: We found that action observation activates specific motor plans in damaged motor circuits after stroke, and this activity is related to motor capability to perform the same actions. Cortical motor activity during action observation may be relevant to motor learning, and to motor relearning in stroke rehabilitation.

Keywords: action observation; mirror neuron system; plasticity; rehabilitation; stroke.

Figures

Figure 1

Main effect of action observation. Brain regions activated during right hand (top) and left hand (bottom) action observation in participants with stroke (red), non-disabled participants (blue), and overlap between groups (violet). Shown at p<.01 uncorrected.

Figure 2

Laterality index of brain activity during action observation. For participants with stroke (top), and non-disabled participants (bottom); during left hand (gray bars) and right hand (black bars) action observation, in regions of interest. Positive values indicate left hemisphere dominance, negative values indicate right hemisphere dominance.

Figure 3

Right versus left hand action observation. Brain regions in participants with stroke and non-disabled participants showing greater activity during right than left hand action observation (top), or left than right hand action observation (bottom). Shown at p<.01 uncorrected.

Figure 4

Brain activity during action observation correlated to motor scores. Positive correlation between mean paretic right hand movement time and activity during right hand action observation in the left inferior frontal gyrus pars opercularis (r(10)=.58, p=.05). Negative correlations between mean paretic right hand FAS score and activity during right hand action observation in the left inferior frontal gyrus pars triangularis (rho(10)=−.79, p=.002) and right precentral gyrus (rho(10)=−.6, p=.04). Point label: Fugl-Meyer Motor Assessment of the Upper Extremity score.

Figure 5

Brain activity during action observation correlated to lesion volume. (a) Positive whole brain correlation (hot) between lesion volume and activity during action observation in the left inferior frontal gyrus pars triangularis (−48, 32, 6); and negative correlations (cool) in the left inferior frontal gyrus pars opercularis (−54, 10, 10) and left dorsal precentral gyrus (−16, −20, 60). Shown at p<.05-.001 uncorrected. Lesion overlap map for participants with stroke involving (b) the internal capsule, and (c) the cortex and internal capsule. Color bar indicates N of 6 in each subgroup.