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A cerebellar substrate for cognition evolved multiple times independently in mammals
Abstract and Figures
ELife digest The brains of mammals consist of the same basic structures, but each of these structures varies from one species to the next. A given structure may be larger in one species than another, for example. It may contain different numbers or sizes of cells. It may even have different connections to other brain regions. By comparing individual brain structures between species, we can map how the mammalian brain has evolved. Smaers et al. have now done this for the cerebellum, a structure at the back of the brain. The mammalian cerebellum consists of three main areas: the vermis, paravermis, and the lateral hemispheres. Smaers et al. show that in apes, dolphins and seals, the lateral hemispheres are unusually large relative to the cerebellum as a whole. This could indicate that these three groups of animals share a common ancestor with enlarged lateral hemispheres. Yet, genetic studies suggest that this is not the case. Another possibility is that apes, dolphins and seals independently evolved enlarged lateral hemispheres. This may have given rise to a trait that proved beneficial for each of them. But what might this be? Studies in people suggest that the lateral hemispheres help to support some forms of learning. Apes, dolphins and seals are among only a few species of mammal with the ability to learn new calls and vocalizations. The expansion of the lateral cerebellum may therefore have contributed to the evolution of vocal learning, and this may have occurred independently on at least three separate occasions. Future work should extend this analysis to other cognitive skills, as well as to other species. Bats, for example, would be of particular interest because of their ability to echolocate. Finally, the lateral hemispheres consist of several subregions that play different roles in learning and information processing. Further experiments should explore whether different subregions have increased in size in different species.
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