Table 1.
Forty-four healthy participants of European descent were included in the study.
Figure 1.
The thermal grill consisted of 8 individual silver plates housed in a PVC unit. The subjects placed their ventral forearm against the grill's surface, orthogonally to the long axis of the silver plates. Temperatures of odd and even numbered plates were set to 41.0°C–42.0°C and/or 15.0°C–16.0°C.
Figure 2.
A) Heat-pain thresholds. The difference between average heat-pain threshold for the high- versus the low 5-HTT-expressing groups was significant [U = 155.0, z = −2.03, p = 0.02, one-tailed test]. B) Cold-pain thresholds. The difference between average cold-pain threshold for the high versus the low 5-HTT-expressing groups was significant [U = 162.0, z = −1.91, p = 0.03, one-tailed test].
Table 2.
Contingency table for heat-pain thresholds.
Table 3.
Contingency table for cold-pain thresholds.
Figure 3.
Validation of the thermal grill illusion for affective and sensory dimensions, all subjects.
The thermal grill illusion was tested along with its constituent temperatures, in a randomized and counterbalanced order. Subjects provided VAS-ratings of both the affective-motivational (i.e. unpleasantness, see panel A) and sensory-discriminatory (i.e. pain, see panel B) dimensions for each condition. Validation of the thermal grill illusion, for all subjects: *** = significant at p<0.001, ** = significant at p<0.01, ns = not significant.
Figure 4.
Thermal grill illusion on the basis of tri-allelic 5-HTTLPR genotype and gender.
Based on our expectations of gender differences, the genotype groups were further divided into females (panel A) and males (panel B). Females differed significantly in ratings of unpleasantness for the thermal grill, * = significant at p<0.05.
Table 4.
Contingency table for perception of the thermal grill illusion (TGI).