Human temporal lobe activation by speech and nonspeech sounds

Functional organization of the lateral temporal cortex in humans is not wel l understood. We recorded blood oxygenation signals from the temporal lobes of normal volunteers using functional magnetic resonance imaging during st imulation with unstructured noise, frequency-modulated (FM) tones, reversed speech, pseudowords and words. For all conditions, subjects performed a ma terial-nonspecific detection response when a train of stimuli began or ceas ed. Dorsal areas surrounding Heschl's gyrus bilaterally, particularly the p lanum temporale and dorsolateral superior temporal gyrus, were more strongl y activated by FM tones than by noise, suggesting a role in processing simp le temporally encoded auditory information. Distinct from these dorsolatera l areas, regions centered in the superior temporal sulcus bilaterally were more activated by speech stimuli than by FM tones. Identical results were o btained in this region using words, pseudowords and reversed speech, sugges ting that the speech-tones activation difference is due to acoustic rather than linguistic factors. In contrast, previous comparisons between word and nonword speech sounds showed left lateralized activation differences in mo re ventral temporal and temporoparietal regions that are likely involved in processing lexical-semantic or syntactic information associated with words . The results indicate functional subdivision of the human lateral temporal cortex and provide a preliminary framework for understanding the cortical processing of speech sounds.