Academic News Report

Background

The motor cortex has long been the focus of research on motor control, mainly studying its role in active motor execution. However, even in the absence of actual motor output, the motor cortex also activates during motor imagery. Previous behavioral and imaging studies have confirmed this phenomenon, but how the specific activity patterns and temporal dynamics in the motor cortex during implicit motor imagery relate to those during actual motor execution remains a mystery. In this paper, the authors explore this issue by recording the intracortical electrical activity of two patients with spinal cord injuries during the execution and imagination of isometric wrist extension movements.

Source of the Paper

This article was published in the April 2024 issue of Nature Human Behaviour with the title “Motor cortex retains and reorients neural dynamics during motor imagery.” The authors include Brian M. Dekleva, Raeed H. Chowdhury, Aaron P. Batista, Steven M. Chase, Byron M. Yu, Michael L. Boninger, and Jennifer L. Collinger, from institutions such as the University of Pittsburgh and Carnegie Mellon University.

Research Details

Research Process

To explore the differences in motor cortex activity between actual and imagined movements, the research team designed an isometric wrist extension task. Participants needed to perform actual and imagined wrist extensions within a fixed framework during the experiment. The research process included the following steps:

1. Experimental Setup: Participants placed their hands in a fixed device with a force sensor and observed a bar showing target force. They needed to generate the corresponding force as instructed during the trials.
2. Data Collection: Trials involving actual movement and motor imagery were conducted separately, each including 36 movements and 36 imaginations, collecting electrical activity from certain areas of the motor cortex.
3. Neural Activity Processing: The recorded neural activity data were dimensionally reduced through preliminary Principal Component Analysis (PCA) to extract significant neural activity subspaces.

Main Results

The results showed that the population activity in the motor cortex could be decomposed into three orthogonal subspaces:

1. Shared Subspace: Active during both actual movement and motor imagery.
2. Action-Unique Subspace: Active only during actual movement.
3. Imagery-Unique Subspace: Active only during motor imagery.

There were significant similarities in the neural dynamics characteristics within these subspaces, especially between the action-unique and imagery-unique subspaces, despite being in orthogonal neural dimensions. During motor imagery, the motor cortex maintained overall population dynamics similar to those of actual execution but redirected the output-related components into a special output-null subspace. This indicates that during motor imagery, the dynamics for motor control and feedback in the motor cortex were reoriented to a unique space that does not produce actual output.

Main Conclusions

The findings suggest that the motor cortex can retain the same neural dynamic structure during motor imagery as during actual execution, providing a beneficial tool for simulated practice within the motor system. This retention of the overall neural dynamic structure may be because the motor cortex’s activity during motor imagery is redirected into orthogonal dimensions that do not produce actual output.

Research Highlights

1. Innovative Methodology: This study successfully separated distinctive neural components in motor imagery and actual movement by dimensionally reducing and decomposing population neural activities into three orthogonal subspaces.
2. Data Support: Experimental evidence showed that the motor cortex maintains overall neural dynamics during motor imagery similar to those during motor execution, providing a new perspective on the role of the motor cortex in motor control.
3. Application Prospects: These findings are of significant importance for motor rehabilitation and brain-computer interface technology, indicating that motor imagery can achieve effects similar to actual motor training, thus providing a potential to improve motor functions.

Additional Information

For readers needing further details and data on the study, the online version of the article and supplementary information can be consulted. Also, related materials can be accessed from the authors’ public repository (such as GitHub).

Conclusion and Value

This article not only reveals how the motor cortex maintains the same neural dynamic structure during motor imagery as during actual motor execution but also shows that activity during motor imagery is redirected into a space that does not produce actual output. This discovery enriches our understanding of the function of the motor cortex and provides new possibilities for the advancement of rehabilitation and brain-computer interface technologies. The results indicate that motor imagery and actual movements share some neural mechanisms, suggesting that motor imagery can serve as an alternative or complement to real motor training, holding significant application value for groups with difficulties in actual movement.