Human Temporal Lobe Activation by Speech and Nonspeech Sounds
J.R. Binder, J.A. Frost, T.A. Hammeke, P.S.F. Bellgowan,
J.A. Springer, J.N. Kaufman and E.T. Possing
Department of Neurology and Department of Cellular Biology,
Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee,
WI, USA
Functional organization of the lateral temporal cortex in humans is
not well understood. We recorded blood oxygenation signals from the
temporal lobes of normal volunteers using functional magnetic
resonance imaging during stimulation with unstructured noise,
frequency-modulated (FM) tones, reversed speech, pseudowords and
words. For all conditions, subjects performed a material- nonspecific
detection response when a train of stimuli began or ceased. Dorsal
areas surrounding Heschl's gyrus bilaterally, particularly the planum
temporale and dorsolateral superior temporal gyrus, were more strongly
activated by FM tones than by noise, suggesting a role in processing
simple temporally encoded auditory information. Distinct from these
dorsolateral areas, regions centered in the superior temporal sulcus
bilaterally were more activated by speech stimuli than by FM
tones. Identical results were obtained in this region using words,
pseudowords and reversed speech, suggesting 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 more
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.
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