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

TLDR

The identification of sounds in primates is thought to rely on anterior projections from primary auditory cortex, analogous to the ventral visual pathway. We sought to identify a comparable route in humans for intelligible speech comprehension. We employed PET imaging to delineate distinct neural subsystems in the human auditory cortex, testing speech and speech‑like stimuli of equal acoustic complexity but differing intelligibility. We found that the left superior temporal sulcus responds to phonetic content, but its anterior portion activates only with intelligible stimuli, revealing a left anterior temporal pathway for speech comprehension.

Abstract

It has been proposed that the identification of sounds, including species-specific vocalizations, by primates depends on anterior projections from the primary auditory cortex, an auditory pathway analogous to the ventral route proposed for the visual identification of objects. We have identified a similar route in the human for understanding intelligible speech. Using PET imaging to identify separable neural subsystems within the human auditory cortex, 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 information, but its anterior part only responds if the stimulus is also intelligible. This novel observation demonstrates a left anterior temporal pathway for speech comprehension.