Abstract
Prior knowledge changes how the brain processes sensory input. Whether knowledge influences initial sensory processing upstream of the brain, in the spinal cord, is unknown. Studying electric potentials recorded invasively and noninvasively from the human spinal cord at millisecond resolution, we find that the cord generates electric potentials at 600 hertz that are modulated by prior knowledge about the time of sensory input, as early as 13 to 16 milliseconds after stimulation. Our results reveal that already in the spinal cord, sensory processing is under top-down, cognitive control, and that 600-hertz signals, which have been identified as a macroscopic marker of population spiking in other regions of the nervous system, play a role in early, context-dependent sensory processing. The possibility to examine these signals noninvasively in humans opens up avenues for research into the physiology of the spinal cord and its interaction with the brain.