BOLD responses to itch in the human spinal cord.

Itch is an independent sensory modality and a very common symptom with manifold causes. However, the neuronal representation of itch perception in the central nervous system is not entirely understood and there is hardly any knowledge about neuronal correlates of itch in the human spinal cord. In the present study we aimed to identify itch-related neural activity in the cervical spinal cord in healthy volunteers employing high-resolution functional magnetic resonance imaging (fMRI). We studied histamine-induced itch on the radial forearm and modulated itch intensity by non-noxious cooling. To control for effects of thermal stimulation (i.e., cooling), volunteers also underwent an identical session without histamine. We studied histamine-induced itch on the radial forearm, by using a block design with alternating blocks of non-noxious cooling separated by blocks of skin temperature. Non-noxious cooling of histamine-treated skin compared to cooling of non-treated skin led to a significant increase in itch perception. On the neural level, itch was paralleled by activation in the dorsal horn of the spinal cord at the transition between spinal segment C5 and C6, ipsilateral to the side of stimulation. These results suggest that itch-related neural activity can be assessed noninvasively in humans at the spinal cord.