Descending projections to the auditory midbrain: evolutionary considerations

• Published in: Journal of Comparative Physiology Vol. 209; no. 1; pp. 131 - 143
• Main Authors: Macias, Silvio, Llano, Daniel A.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-01-2023; Springer Nature B.V
• Subjects: Acoustic navigation; Amphibians; Amygdala; Animal Physiology; Animals; Auditory Cortex - physiology; Auditory Pathways - physiology; Biomedical and Life Sciences; Cerebral cortex; Cortex (auditory); Hearing; Homology; Inferior Colliculi - physiology; Inferior colliculus; Life Sciences; Mammals; Mechanical properties; Mesencephalon; Modulators; Neurosciences; Pallium; Physiology; Questions; Reptiles & amphibians; Review; Thalamus; Toruses; Zoology; Bat; Inferior colliculus; Frog; Anuran; Thalamus; Corticofugal; Echolocation; Auditory cortex
• ISSN: 0340-7594; 1432-1351
• DOI: 10.1007/s00359-022-01588-5

The mammalian inferior colliculus (IC) is massively innervated by multiple descending projection systems. In addition to a large projection from the auditory cortex (AC) primarily targeting the non-lemniscal portions of the IC, there are less well-characterized projections from non-auditory regions of the cortex, amygdala, posterior thalamus and the brachium of the IC. By comparison, the frog auditory midbrain, known as the torus semicircularis, is a large auditory integration center that also receives descending input, but primarily from the posterior thalamus and without a projection from a putative cortical homolog: the dorsal pallium. Although descending projections have been implicated in many types of behaviors, a unified understanding of their function has not yet emerged. Here, we take a comparative approach to understanding the various top-down modulators of the IC to gain insights into their functions. One key question that we identify is whether thalamotectal projections in mammals and amphibians are homologous and whether they interact with evolutionarily more newly derived projections from the cerebral cortex. We also consider the behavioral significance of these descending pathways, given anurans’ ability to navigate complex acoustic landscapes without the benefit of a corticocollicular projection. Finally, we suggest experimental approaches to answer these questions.