A study in Nature finds that corticospinal neurons originating in the brain's somatosensory cortex influence touch sensitivity, and may be responsible for the intense pain some people with nerve injury feel from the lightest touch. In this schematic, nerve fibers bringing touch information from the brush of a feather (A) send the sensory information to the brain (via a relay in the midbrain) but also activate an interneuron (shown in red) in the spinal cord's dorsal horn. The pathway then ascends upward to the brain (B), activating S1 corticospinal neurons in the somatosensory cortex (C). These S1 neurons, shown in green, descend to the spinal cord (D) and communicate with the same interneuron, which amplifies the touch signal. The graph (E) shows the interneuron's electrophysiologic activity when stimulated by the feather (blue line), and amplification of this signal (green line) in response to additional inputs from S1 corticospinal neurons. In people with neuropathic pain, the amplified touch signal is perceived as pain.