Identification of a pathway for intelligible speech in the left temporal lobe

It has been proposed that the identification of sounds, including species-s pecific vocalizations, by primates depends on anterior projections from the primary auditory cortex, an auditory pathway analogous to the ventral rout e proposed for the visual identification of objects. We have identified a s imilar route in the human for understanding intelligible speech. Using PET imaging to identify separable neural subsystems within the human auditory c ortex, we used a variety of speech and speech-like stimuli with equivalent acoustic complexity but varying intelligibility. We have demonstrated that the left superior temporal sulcus responds to the presence of phonetic info rmation, but its anterior part only responds if the stimulus is also Intell igible. This novel observation demonstrates a left anterior temporal pathwa y for speech comprehension.