Spatial organization of frequency preference and selectivity in the human inferior colliculus

To date, the functional organization of human auditory sub-cortical structures can only be inferred from animal models. Here we use high-resolution functional MRI at ultra-high magnetic fields (7 Tesla) to map the organization of spectral responses in the human inferior colliculus (hIC), a sub-cortical structure fundamental for sound processing. We reveal a tonotopic map with a spatial gradient of preferred frequencies approximately oriented from dorso-lateral (low frequencies) to ventro-medial (high frequencies) locations. Furthermore, we observe a spatial organization of spectral selectivity (tuning) of fMRI responses in the hIC. Along isofrequency contours, fMRI-tuning is narrowest in central locations and broadest in the surrounding regions. Finally, by comparing sub-cortical and cortical auditory areas we show that fMRI-tuning is narrower in hIC than on the cortical surface. Our findings pave the way to non-invasive investigations of sound processing in human sub-cortical nuclei and to studying the interplay between sub-cortical and cortical neuronal populations.