The ARC-IM (Adaptive Rehabilitation and Control - Implanted) is ONWARD Medical's implantable epidural spinal cord stimulation platform. Originally developed for restoring movement in people with spinal cord injury through targeted spinal stimulation, ARC-IM gained global attention when it was used as the spinal stimulation component of the brain-spine digital bridge demonstrated by Lorach et al. in 2023 — enabling a man with complete paralysis to walk by thought alone.

Technology

ARC-IM consists of:

  • Implantable pulse generator (IPG): A battery-powered neurostimulator implanted in the abdomen
  • Epidural electrode array: A multi-contact electrode paddle placed on the dorsal surface of the spinal cord in the epidural space, targeting the lumbosacral spinal segments that control leg movement
  • Stimulation programs: Configured to activate specific spinal motor pools corresponding to hip flexion, knee extension, ankle dorsiflexion, and other movements required for walking

Brain-Spine Digital Bridge

In the landmark Lorach et al. (2023) study published in Nature, ARC-IM was paired with a cortical BCI (Utah Array recording from motor cortex) to create a "digital bridge" across the spinal cord injury:

  1. The participant thinks about walking
  2. Motor cortex signals are recorded by the Utah Array and decoded in real time
  3. Decoded movement intentions are translated into stimulation commands
  4. ARC-IM delivers targeted epidural stimulation to the appropriate spinal segments
  5. The spinal circuits activate leg muscles, producing coordinated stepping

This brain-spine interface enabled the participant to walk over ground, climb stairs, and navigate complex terrain — all driven by thought-controlled spinal stimulation.

Clinical Development

ONWARD Medical is pursuing regulatory approval for ARC-IM for spinal cord injury rehabilitation. The system has also shown benefit for blood pressure regulation (autonomic function) in SCI patients. The combination of cortical BCI with spinal stimulation represents a new paradigm — using BCI not to control an external device but to reanimate the body's own motor systems.

Significance for BCI

ARC-IM demonstrates that BCI output does not have to be a computer cursor or robotic arm. By routing decoded brain signals to the spinal cord below the injury, the digital bridge approach restores natural movement through the body's own muscles — potentially a more intuitive and functional outcome than controlling external devices.