Animal Models of Speech and Language Disorders

Book excerpt: Basic research over the last decade or two has uncovered similarities between speech, especially its sensori-motor aspects, and vocal communication in several non-human species. The most comprehensive studies so far have been conducted in songbirds. Songbirds offer us a model system to study the interactions between developmental or genetic predispositions and tutor-dependent influences, on the learning of vocal communication. Songbird research has elucidated cellular and molecular mechanisms underlying learning and production of vocal patterns, perception of vocal sounds, vocal motor control and vocal neuromotor plasticity. More recently, the entire genome of the songbird zebra finch has been sequenced. These discoveries, along with the identification of several genes implicated in familial human speech and language disorders, have made it possible to look for analogues of speech and language dysfunction in zebra finches, at least at the perceptual and sensori-motor levels. Two approaches in particular have led us closer to the development of animal models of human speech conditions, namely developmental stuttering and a familial verbal dyspraxia associated with a mutation in the gene for the transcription factor FoxP2. Work on other animals that show developmental sensori-motor learning of vocal sounds used for communication have also shown significant progress, leading to the possibility of development of models of speech and language dysfunction in them. Among mammals, the principal ones include dolphins and whales. In non-human primates, while vocal learning per se is not very prominent, investigations on their communicative abilities have thrown some light on the rudiments of language. These considerations make the publication of a book focused on animal models of speech and language disorders, detailing the overall investigative approach of neurobehavioral studies in animals capable of vocal communication and learned vocalizations, a much-needed and worthwhile project. It would serve as a unifying review of research in this new multidisciplinary frontier, spanning the molecular to the behavioral, for clinicians and researchers, as well as a teaching resource for advanced speech pathology and neuroscience students. This book will also be the first of its kind.