Effects of heating on the psychophysical variables.

<p>The whole dorsal surface of the hand was warmed to 38°C by means of an infrared lamp. <b>- A</b> Individual example. Relationship ΔAT² = (AT−T₀)² = f(α) which allowed one to determine the psychophysical thresholds T_ψ. A dotted purple line marks the limit slopes α_AC that delineate the Aδ- from the C-response domains. The shift of the straight lines ΔAT² = f(α) during heating is misleading because the base temperatures were very different. The heat indeed elicited an increase of Tψ_C and Tψ_A thresholds by about 3°C. <b>- B</b> Corresponding relationship t_R = f(1/α) which allowed one to determine the psychophysical latencies Lψ. Note the variations of the slopes of the straight lines t_R = f(1/α) following heating without any modification of the intercept with the ordinate, which means that the psychophysical latencies were not modified by heating. <b>- C</b> Curves in the plane [T₀, α] which delimit the domains for obtaining responses triggered by Aδ- and C-fibers, respectively (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010269#pone-0010269-g004" target="_blank">Fig. 4</a>); the purple full circles correspond to the values determined experimentally. Curves are calculated from the Tψ_C Tψ_A, Lψ_C and Lψ_A values, all determined experimentally as the point of coordinates [T₀, α_AC]. One can see a shift of the respective domains of the responses elicited by Aδ- and C-fibers to the advantage of the latter. <b>- D</b> Identical results shown in the plane [T₀, α_AC^0.5]. E. Overall mean results regarding physical (T₀) and psychophysical (Tψ_A, Tψ_C, Lψ_A, Lψ_C and α_AC) variables (* = p<0.05; Wilcoxon-Mann-Whitney test).