Lip-reading ability and patterns of cortical activation studied using fMRI

Lip-reading is a complex cognitive skill with large individual differences in performance. The basis of these individual differences remains poorly understood. Functional magnetic resonance imaging (fMRI) techniques allows brain activation accompanying complex cognitive activities to be studied noninvasively. In the present paper, fMRI was used to study the patterns of cortical activation that occur during the silent lip-reading of connected speech and to investigate whether there are detectable differences in activation between subjects with widely differing lip-reading abilities. From a cohort of 26 volunteers, nine subjects who fell into three distinct lip-reading ability groups were selected. Brain activation was measured in two conditions: an experimental condition where subjects attempted to lip-read sentences; and a baseline condition where subjects passively viewed a static image of a talker's face. Relative to the baseline condition, lip-reading induced activation in several cortical areas, including the auditory cortices, despite the lack of an auditory component to the task. In comparison to the better two groups of lip-readers, subjects in the poorest group displayed significantly less activation in superior and middle temporal gyrus, but not inferior temporal gyrus. These preliminary results justify more extensive investigations of the cortical basis of individual differences in lip-reading.