Detection of early-onset nocifensive behaviors prior to withdrawal of stimulated limb. A 100 msec thermal pulse at high power (6.08 W/mm2) was used to stimulate the right index toe. Withdrawal responses were recorded at a rate of 500 frames per second. The position of the rat's head before and after stimulation are highlighted in A and B, respectively. The upper and lower arrowheads in each frame bring attention to the eyes and nose, respectively. Abrupt head displacement in (A) versus (B) occurs by 110 msec (140-30 msec, see Methods). Also note in B the orbital "tightening", which was observed only with some rats following laser stimulation. (C) By 210 msec, the head was oriented towards the stimulated foot and toes on the stimulated foot have moved. (D) Withdrawal of the stimulated paw was underway by 310 msec. (E) and (F) are magnifications of (A) and (B), respectively, showing that by 110 msec, toe movement on the non-stimulated hind paw has preceded any movement detected in the stimulated limb. Full videos can be viewed in the Additional file 1 Movie S1 data and show that latency to the first detectable movement was approximately 74 msec.
Mitchell et al. Molecular Pain 2010 6:94 doi:10.1186/1744-8069-6-94