Is it necessary to show virtual limbs in action observation neurorehabilitation systems?

Abstract

Introduction: Action observation neurorehabilitation systems are usually based on the observation of a virtual limb performing different kinds of actions. In this way, the activity in the frontoparietal Mirror Neuron System is enhanced, which can be helpful to rehabilitate stroke patients. However, the presence of limbs in such systems might not be necessary to produce mirror activity, for example, frontoparietal mirror activity can be produced just by the observation of virtual tool movements. The objective of this work was to explore to what point the presence of a virtual limb impacts the Mirror Neuron System activity in neurorehabilitation systems.

Methods: The study was conducted by using an action observation neurorehabilitation task during a functional magnetic resonance imaging (fMRI) experiment with healthy volunteers and comparing two action observation conditions that: 1 - included or 2 - did not include a virtual limb.

Results: It was found that activity in the Mirror Neuron System was similar during both conditions (i.e. virtual limb present or absent).

Conclusions: These results open up the possibility of using new tasks that do not include virtual limbs in action observation neurorehabilitation environments, which can give more freedom to develop such systems.

Keywords: action observation; fMRI; mirror neurons; neurorehabilitation; virtual limbs; virtual reality.

Figure 1.

The action observation task. Participants observed movements of a virtual limb with a red dot under the tip of the middle finger (hand condition, shown here), or equivalent movements of the red dot alone (dot condition). In both cases, the red dot moves to reach the figure indicated in the left top corner of the screen.

Figure 2.

The action observation neurorehabilitation task was associated with an increase of activity in the Mirror Neuron System when the virtual hand was moving but also when the virtual hand was absent and just the dot was moving. Blue voxels were activated only in hand condition (hand > fix contrast); red voxels were activated only in dot condition (dot > fix contrast); violet voxels depict regions activated in both conditions (both contrasts). The contrasts hand > dot and dot > hand did not show significant results. Group analysis, N = 14, threshold: p < 0.05 at the voxel level, false discovery rate corrected for multiple comparisons; minimum cluster size = 25 voxels.