Neurobiology: The neural basis of vocal learning
In terms of vocal learning humans and bats have much in common. In a new international project, neurobiologists Uwe Firzlaff from the Technical University of Munich (TUM) and Lutz Wiegrebe from the Ludwig-Maximilians-Universität München (LMU) hope to establish bats as a model for the study of vocal learning in mammals.
Vocal learning is a prerequisite for language acquisition in humans. But how this process actually functions remains quite mysterious, as the neuronal mechanisms that underlie vocal learning in mammals remain poorly understood. To remedy this situation, Dr. Uwe Firzlaff from the Chair of Zoology at TUM and Professor Lutz Wiegrebe from the Department of Neurobiology in the Faculty of Biology at LMU, in collaboration with colleagues in California and the Netherlands, have embarked on an ambitious project. Working independently on four aspects of the problem, the Munich researchers, together with Dr. Sonja Vernes of the Max Planck Institute for Psycholinguistics in Nijmegen and Professor Michael Yartsev of the University of California in Berkeley, hope to establish bats as an experimental model system for the study of vocal learning. The scientists have received a grant worth 1.2 million dollars over the coming 3 years from the Human Frontiers Science Program.
In most cases, the repertoire of sounds that an animal can produce is genetically programmed. But humans not only have the capacity to imitate sounds that they hear, they also learn to assign a semantic meaning to them, and this is a precondition for verbal communication. The ability to learn and reproduce sounds is not unique to our own species. Toothed whales, bats and a few other mammalian species, as well as birds such as parrots and songbirds, can also learn new sound sequences by imitation. Vocal learning in songbirds has been extensively investigated in recent years, primarily in zebra finches. However, birds diverged from mammals very early in vertebrate evolution. Hence the degree to which the findings in zebra finches can be translated to mammals remains unclear.
However, there is as yet no established experimental system in which the neuronal basis for vocal learning in mammals can be studied in detail. “Bats are particularly suitable for this purpose. Like humans, bats produce a broad array of sounds during early post-natal development. As they get older, they begin to imitate the sounds made by their mothers. No other laboratory animal exhibits this behavior,” says Lutz Wiegrebe. “Moreover, while auditory-vocal coupling – the feedback interaction between sounds heard and self-generated sounds – has been relatively well studied in bats, much less is known about the neuronal processes involved in vocal learning,” adds Uwe Firzlaff. In addition, the FoxP2 gene, which has been linked to language learning in humans, has undergone a striking degree of evolutionary divergence in echolocating bats relative to other mammals, and Dr. Sonja Vernes is pursuing this topic further.
The researchers hope that the results obtained during the project will enable them to establish an animal model for vocal learning which is phylogenetically closer to humans than the popular zebra finch model. In addition they hope to determine the neurobiological and genetic bases of vocal learning, and define the differences and commonalities that characterize vocal learning in birds and mammals and how vocalizations are encoded in trains of nerve impulses.