Mechanisms of rhythm generation of the human lumbar spinal cord in response to tonic stimulation without and with step-related sensory feedback
Minassian K, Hofstoetter US, Danner SM, Mayr W, McKay WB, Tansey K, Dimitrijevic MR
Independent studies have shown that the human lumbar spinal networks below a complete spinal cord injury can produce rhythmic motor outputs in response to step-related sensory feedback or sustained electrical spinal cord stimulation (SCS). Here we present our current studies applying lumbar SCS in motor-complete spinal cord injured (SCI) individuals in the supine and supported standing position, and during assisted treadmill stepping, to explore the mechanisms of spinal rhythm generation. SCS could produce rhythmic EMG activities without step-related sensory feedback; in each case, all muscles were active with a common rhythm frequency. During SCS and passive treadmill stepping, muscle activities were normally synchronized to the imposed step frequency, but activities with an independent rhythm frequency were generated as well. The results suggest rhythmic reflex actions and central spinal generation as two different causes of rhythm generation.