Uncertainty about the intensity of impending pain increases ensuing pain responses in congenital blindness

We have shown that congenitally blind individuals are more sensitive to painful heat compared to their sighted counterparts. This hypersensitivity might be at least partly mediated by psychological and cognitive factors, such as pain expectation and anxiety. Here we investigate whether uncertainty about the intensity of a pending painful stimulus affects pain differently in congenitally blind and sighted control subjects. We measured pain and anxiety in a group of 11 congenitally blind and 11 age- and sex-matched normal sighted control participants. Painful stimuli were delivered under two psychological conditions, whereby participants were either certain or uncertain about the intensity of a pending noxious stimuli. Although both blind and sighted participants had increased anxiety ratings in the uncertain condition, pain ratings increased only in the congenitally blind participants. Our data therefore indicate that increased anxiety levels have a stronger influence on the perceived pain intensity in blind individuals, possibly because they allocate greater attention to signals of external threat.