Processing of Attended and Unattended Frequencies in the Human Auditory Cortex.

Abstract:
Different scalp distributions for attention-related activity in event-related brain potentials (ERPs) to tones of different frequencies have suggested attentional modulation of auditory processing in tonotopically organized areas of the human auditory cortex (e.g., Woods et al., Psychophysiology, 1993, 30, 287-295; Alho et al., Biol. Psychol., 1994, 38, 73-90). To clarify this issue, functional magnetic resonance imaging (fMRI) with Marconi Eclipse 1.5-Tesla fMRI system was used to record hemodynamic brain responses of young healthy adults to attended and unattended sounds in different frequency ranges. In each experimental condition, the subjects were presented with a monaural sequence of sounds varying in frequency within a small range (8 semitones) centered at 250, 1000, or 4000 Hz. The subjects attended either to the auditory stimulus sequence or to a sequence of visual stimuli with varying shapes in order to detect stimulus repetitions in the attended sequence. Comparisons of auditory cortex activity associated with processing of sounds at different frequency ranges during the auditory and visual attention conditions will be reported. These comparisons will clarify whether fMRI may be used to map the tonotopy of the auditory cortex and to localize attentional modulation of auditory processing in tonotopic or non-tonotopic cortical fields.