  Current treatments for paraplegia induced by spinal cord injury (SCI) are
often limited by the severity of the injury. The accompanying loss of sensory
and motor functions often results in reliance on wheelchairs, which in turn
causes reduced quality of life and increased risk of co-morbidities. While
brain-computer interfaces (BCIs) for ambulation have shown promise in restoring
or replacing lower extremity motor functions, none so far have simultaneously
implemented sensory feedback functions. Additionally, many existing BCIs for
ambulation rely on bulky external hardware that make them ill-suited for
non-research settings. Here, we present an embedded bi-directional BCI (BDBCI),
that restores motor function by enabling neural control over a robotic gait
exoskeleton (RGE) and delivers sensory feedback via direct cortical electrical
stimulation (DCES) in response to RGE leg swing. A first demonstration with
this system was performed with a single subject implanted with
electrocorticography electrodes, achieving an average lag-optimized
cross-correlation of 0.80$\pm$0.08 between cues and decoded states over 5 runs.
