Differential fMRI responses in the left posterior superior temporal gyrus and left supramarginal gyrus to habituation and change detection in syllables and tones

Using a habituation-recovery paradigm adapted to functional magnetic resonance imaging, we investigated the brain responses to syllables and tones in six right-handed male subjects. We opposed a standard condition (STD) in which the subjects were listening to homogeneous sequences of four identical stimuli, to a deviant condition (DEV) in which the fourth stimulus of the sequence differed in pitch or spectral content for tones and in the initial stop consonant for syllables. The corresponding runs alternated four rest periods with two STD and two DEV conditions. In addition to a marked rightward asymmetry in the primary and secondary auditory cortex for tones and a right inferior frontal activation for the tone condition where the deviant had increased spectral content, the experiment revealed differential activations in the left posterior superior temporal gyrus and in the left supramarginal gyrus. Activations within the left posterior superior temporal gyrus were observed for the DEV condition with tones and for the STD and DEV conditions with syllables. Activation within the inferior part of the left supramarginal gyrus was only observed for the DEV condition with syllables. The analysis of the decreases and increases in the BOLD signal across the STD, DEV, and rest conditions suggests that the left posterior superior temporal gyrus is implicated in the preattentive change detection of acoustic changes in speech as well as nonspeech stimuli, whereas the left supramarginal gyrus is more specifically engaged in the detection of changes in phonological units.