Itching-related somatosensory evoked potentials.

Electrically evoked itching has the strong potential to be used to investigate the central processing associated with itching at high temporal resolution by employing magnetoencephalography, electroencephalography (EEG), and event-related functional magnetic resonance imaging. However, it has not been investigated whether time-locked brain activity can be measured using this stimulus, and whether the itching sensation induced by electrical stimulation of the skin is associated with C-fibers. Thus, we investigated these problems in this study. Itching sensations were elicited when electrical stimuli were applied to the skin of the right wrist and right forearm. EEG activity was recorded from 5 electrodes (Fz, FCz, Cz, CPz and Pz). When the right wrist was stimulated, the reaction time (RT) and latency of the positive component of somatosensory evoked potentials (P1) were 1215 ms and 963 ms, respectively. When the right forearm was stimulated, the RT and peak latency of the P1 were 1013 ms and 772 ms, respectively. The conduction velocity estimated from the RT and latency of the P1 was 1.04 m/s and 0.92 m/s, respectively. In addition, the itching sensation and P1 were inhibited when the current intensity was increased into the range eliciting pain and touch sensations, implying interaction between C- and A-fibers. These findings demonstrate that time-locked brain activity can be measured using electrically evoked itching and that the itching sensation induced by the electrically evoked itching is associated with C-fibers. Thus, this method is useful for research into the central processing of itching.