Activation Patterns of Human Auditory Cortex by Various Sounds: A fMRI Study

Abstract

BACKGROUND: Auditory processing by the temporal lobes may involve a functional segregation. However, debate continues concerning the functional asymmetry of auditory processing in humans under different stimulation conditions. The purpose of this study was to elucidate activation patterns of the human brain auditory associated cortices elicited by a serial of sounds. METHODS: Five healthy subjects with normal hearing participated. Five pre-recorded sound tracks were used: a pure tone, a wide-band white noise, sounds of ocean waves, part of Antonio Vivaldi's ”The Four Seasons” concerto No. 1 and a spoken, continuous discourse. Functional magnetic resonance imaging was performed while different sounds were presented binaurally. RESULTS: Characteristic activation patterns were elicited although variability was presented between subjects. Pure tone led to the weakest activation of Heschl's gyrus (HG), bilaterally, mainly on the right. Compared to pure tone, HG activation by white noise and ocean wave sounds was more intense. Ocean wave sounds activated the right superior temporal gyrus (STG) surrounding HG, and the left STG posterior to HG. Classical music activated the entire right superior temporal lobe and the pars opercularis of the inferior frontal gyrus (POIFG). The left HG, anterior and posterior parts of the STG, and the POIFG were weakly activated. Speech activated the entire STG, superior temporal sulcus, and middle temporal gyrus bilaterally, but slightly on the left, with extension toward the left inferior frontal gyrus and planum temporale. CONCLUSIONS: A lateralization for activation of the right by non-speech sounds and the left by speech was detected. Our results support the hypothesis that the anterior and posterior parts of the STG are responsible for complex sound analysis.