To date, the functional organization of human auditory subcortical structures can only be inferred from animal models. Here we use high-resolution functional magnetic resonance imaging at ultra-high magnetic fields (7T) to map the organization of spectral responses in the human inferior colliculus, a subcortical structure fundamental for sound processing. We reveal a tonotopic map with a spatial gradient of preferred frequencies approximately oriented from dorsolateral (low frequencies) to ventromedial (high frequencies) locations. Furthermore, we observe a spatial organization of spectral selectivity (tuning) of functional magnetic resonance imaging responses in the human inferior colliculus. Along isofrequency contours, functional magnetic resonance imaging tuning is narrowest in central locations and broadest in the surrounding regions. Finally, by comparing subcortical and cortical auditory areas we show that functional magnetic resonance imaging tuning is narrower in human inferior colliculus than on the cortical surface. Our findings pave the way to noninvasive investigations of sound processing in human subcortical nuclei and for studying the interplay between subcortical and cortical neuronal populations.
Bibliographical noteFunding Information:
This work was supported in part by the National Institutes of Health (grants, P30 NS057091, NINDS institutional Center Core Grant P30 NS076408, Biotechnology Research Center (BTRC) (NCRR) P41 RR08079 and (NIBIB) P41 EB015894), the W.M. Keck Foundation, and MIND institute. The 7T magnet purchase was funded in part by NSF DBI-9907842 and NIH S10 RR1395.