Temperature gradient between the rectum and the anal canal: Evidence against the role of temperature sensation as a sensory modality in the anal canal of normal subjects

Temperature difference between the rectum and anal canal is a fundamental requirement for the hypothesis that temperature sensation is of physiological importance in discrimination of anorectal contents occurring during the 'sampling reflex'. The temperature gradient between the rectum and the anal canal was measured in 47 normal subjects (mean age 51.6 years +/- 16.8 s.d., 24 men). The maximum mean difference in temperature between the rectum and the anal canal was 0.13 degrees C (0.06-0.19, 95 per cent confidence intervals) and occurred 4 cm from the anal verge. This difference is too small to be detected by the anal canal mucosa. Under normal physiological circumstances the conscious appreciation of temperature of faeces passing from the rectum to the anal canal is impossible during the anorectal sampling reflex.