Mini-review: The neural circuits of the non-lemniscal inferior colliculus.

The inferior colliculus (IC) is a critical hub of the central auditory system (CAS), and a majority of the ascending and descending auditory synapses converge in the IC. With considerable methodological advances in neural tract tracing techniques, one can clearly visualize various sub-compartments of the IC. Herein, we compared the inputs and outputs between the two sub-regions of the non-lemniscal IC, namely, the dorsal and external cortex of the IC. The non-lemniscal IC plays a crucial role in multisensory integration and animal behavior, and the dorsal and external regions are distinct in many aspects, including molecular expression and neural circuits. They may serve integration and regulation functions via parallel pathways. As previous studies have mostly treated these two parts as a whole, we suggest that the two sub-regions of the non-lemniscal IC should be studied separately in future IC functional investigations.