Imaging Cross-Modal Influences in Auditory Cortex

Recent studies have made considerable progress in understanding how our brain combines the information from different sensory modalities and much evidence about the cortical regions involved has been provided by functional magnetic resonance imaging. Imaging studies have, for example, shown that cross-modal influences occur already at early stages of auditory cortex. However, given our still limited understanding of the functional organization of human auditory cortex, these results are often to interpret with respect to the exact localization of cross-modal influences. Here we discuss a localization technique, which provides a functional map of individual fields in the auditory cortex of individual subjects. Using high-resolution imaging techniques in an animal model with known organization of auditory cortex, we proved the feasibility of this functional mapping technique and demonstrated its use in localizing cross-modal influences to individual auditory fields. Our results show that cross-modal influences already occur in secondary auditory cortices and increase along the auditory processing hierarchy. While these results provide good evidence that auditory processing can be affected by non-acoustic stimuli very early on, we also discuss the interpretability of these findings with regard to the underlying neuronal activity, which is considerable hampered by the still unknown neural basis of the fMRI signal