Reanimating the arm and hand with intraspinal microstimulation.

Area of Science:

• Neuroscience
• Spinal Cord Injury Research
• Brain-Machine Interfaces

Background:

• Spinal cord injury (SCI) currently lacks effective therapies, leaving many patients with impaired arm and hand function.
• Previous research on intraspinal microstimulation (ISMS) has primarily focused on non-primate models, with limited understanding of its effects on primate upper limbs.
• Restoring upper-limb function is crucial for improving the quality of life for individuals with SCI.

Purpose of the Study:

• To investigate the effects of intraspinal microstimulation (ISMS) on upper-limb motor responses in non-human primates.
• To determine if ISMS can elicit functional arm and hand movements in the macaque spinal cord.
• To develop a model for predicting and controlling ISMS-evoked movements for potential therapeutic applications.

Main Methods:

• Delivered long trains of intraspinal microstimulation (ISMS) to the cervical spinal cord of macaques.
• Analyzed the evoked motor responses, including complex and coordinated arm and hand movements.
• Developed and validated a dual exponential model to describe ISMS motor responses based on stimulation history.

Main Results:

• Demonstrated for the first time that ISMS can evoke functional arm and hand movements in the primate spinal cord.
• Showed that complex, multi-muscle movements could be elicited from a single electrode.
• Achieved independent control of reaching and grasping movements using only two electrodes.
• Characterized ISMS motor responses using a dual exponential model dependent on stimulation history.
• Successfully inverted the model to generate stimulus trains for arbitrary, graded motor responses.

Conclusions:

• Intraspinal microstimulation (ISMS) is a viable method for evoking functional upper-limb movements in primates.
• A predictive model based on stimulation history allows for precise control over ISMS-evoked movements.
• This approach holds significant promise for developing closed-loop brain-machine interfaces to restore volitional movement after spinal cord injury.