Individual variability in functional organization of the human and monkey auditory cortex

Accumulating evidence shows that auditory cortex (AC) of humans, and other primates, is involved in more complex cognitive processes than feature segregation only, which are shaped by experience-dependent plasticity and thus likely show substantial individual variability. However, thus far, individual variability of ACs has been considered a methodological impediment rather than a phenomenon of theoretical importance. Here, we examined the variability of ACs using intrinsic functional connectivity patterns in humans and macaques. Our results demonstrate that in humans, functional variability is 1) greater near the non-primary than primary ACs, 2) greater in ACs than comparable visual areas, and 3) greater in the left than right ACs. Remarkably similar modality differences and lateralization of variability were observed in macaques. These connectivity-based findings are consistent with a confirmatory task-based fMRI analysis. The quantitative proof of the exceptional variability of ACs has implications for understanding the evolution of advanced auditory functions in humans.