Noxious cold evokes multiple sensations with distinct time courses

A noxious cold stimulus can evoke multiple sensations each occurring with a different time course. We have performed psychophysical studies to identify the time course of five sensations evoked by a noxious cold stimulus applied to the hand. Subjects continuously rated either pain, ache, cold, heat or prickle sensations throughout repeated presentations of a noxious cold stimulus (3 degrees C) from a neutral (32 degrees C) baseline. Separate runs were used to assess each of the five types of sensation. Cold was reported throughout the period of cooling. The time course of pain and ache sensations were similar. However, prickle and heat sensations had time courses that could be distinguished from each other, and from ache and pain. Identification of these temporal profiles could provide clues to their underlying mechanisms. The temporal dissociation of these sensations will also enable neuroimaging studies of the cortical mechanisms associated with these sensations. Thus our results constitute a first step toward identifying the distinct modes of neural activity associated with different types of pain sensation.