Neural responses to silent lipreading in normal hearing male and female subjects

In the past, researchers investigated silent lipreading in normal hearing subjects with functional neuroimaging tools and showed how the brain processes visual stimuli that are normally accompanied by an auditory counterpart. Previously, we showed activation differences between males and females in primary auditory cortex during silent lipreading, i.e. only the female group significantly activated the primary auditory region during lipreading. Here we report and discuss the overall activation pattern in males and females. We used positron emission tomography to study silent lipreading in 19 normal hearing subjects (nine females). Prior to scanning, subjects were tested on their lipreading ability and only good lipreaders were included in the study. Silent lipreading was compared with a static image. In the whole group, activations were found mainly in the left hemisphere with major clusters in superior temporal, inferior parietal, inferior frontal and precentral regions. The female group showed more clusters and these clusters were larger than in the male group. Sex differences were found mainly in right inferior frontal and left inferior parietal regions and to a lesser extent in bilateral angular and precentral gyri. The sex differences in the parietal multimodal region support our previous hypothesis that the male and female brain process visual speech stimuli differently without differences in overt lipreading ability. Specifically, females associate the visual speech image with the corresponding auditory speech sound whereas males focus more on the visual image itself.