To date it remains largely unknown how fundamental aspects of natural sounds, such as their spectral content and location in space, are processed in human subcortical structures. Here we exploited the high sensitivity and specificity of high field fMRI (7 Tesla) to examine the human inferior colliculus (IC) and medial geniculate body (MGB). Subcortical responses to natural sounds were well explained by an encoding model of sound processing that represented frequency and location jointly. Frequency tuning was organized in one tonotopic gradient in the IC, whereas two tonotopic maps characterized the MGB reflecting two MGB subdivisions. In contrast, no topographic pattern of preferred location was detected, beyond an overall preference for peripheral (as opposed to central) and contralateral locations. Our findings suggest the functional organization of frequency and location processing in human subcortical auditory structures, and pave the way for studying the subcortical to cortical interaction required to create coherent auditory percepts.
Bibliographical noteFunding Information:
We thank K. Derey for characterization of the virtual reality lab and the recorded sounds. This work was supported by the Netherlands Organization for Scientific Research (NWO; Rubicon grant 446-12-010 to M.M., VIDI grant 864-13-012 to F.D.M. and VICI grant 453-12-002 to E.F.), the National Institutes of Health (NIH grants P41 EB015894, P30 NS076408, and S10 RR026783), and the WM KECK Foundation.