Activation in primary auditory cortex during silent lipreading is determined by sex

Recent studies investigating whether the primary auditory cortex (PAC) is involved in silent lipreading gave inconsistent results. We used positron emission tomography to identify which areas in the temporal lobe process visible speech, with a focus on the PAC. Subjects were tested on lipreading numbers and only the best lipreaders were included in the study (n = 18; 9 female, 9 male). Each subject was scanned while either watching a movie with a speaker silently articulating numbers (lipreading condition) or watching a static image of the same speaker (baseline condition). Subjects were instructed to repeat internally the number seen or the number '1'. Compared to the baseline condition, silent lipreading activated temporal areas in both hemispheres with the largest activation clusters in the left hemisphere. When the whole group was examined, no activation in the PAC was found. But when investigating the two sexes separately, the female group demonstrated activation of the left PAC. There was no significant activation in the right female PAC or in the left and right male PAC. Since both groups had similar performances in lipreading, differential activity in the PAC has no effect on lipreading scores. These results may explain previous inconsistent results where no differentiation for sex was made.