This interaction connects FOXP2 with language disorders with which it was not otherwise implicated. The Amylin (rat) FoxP2-CNTNAP2 molecular story illustrates how genes linked to language impairments, or to other disorders in which language deficits are prominent, can be fruitfully investigated in songbirds to determine their impact on the vocal learning subsystem and its underlying neural circuitry. CASPR2, songbird model, Fragile X == Introduction == In 1988, Noam Chomsky pondered, Perhaps at some time hundreds of thousands of years ago, some small change took place, some mutation took place in the cells of prehuman organisms. And for reasons of physics which are not yet understood, that led to the representation in the mind/brain of the mechanisms of discrete infinity, the basic concept of language and also of the number system. (Chomsky 1988). Today, the idea that such a change was restricted to a single molecule and occurred solely in the hominid lineage, referred to as the Grammar Gene’ theory, is deemed an extreme position (Bishop 2009). Rather, the brain system underlying language is likely made up of subsystems, forms of which exist in other taxonomic groups. Language could have arisen in humans as a consequence of the unique intersection of these subsystems. A subsystem identified in non-humans could represent the homologous component in language. Alternatively, if the subsystem emerged at a point that does not feed into the hominid lineage, it could represent convergent or parallel (homoplasous) evolution whereby similar selection pressures drive parallel instances of similar biological solutions Amylin (rat) (as we, and others (e.gJarvis 2004), have argued for birdsong and speech). Whether homologous or homoplasous, the good news is that this viewpoint opens the door for studying subsystems of language at the biological level using a comparative approach. This chapter examines one language subsystem, namely the capacity for vocal learning, and the genes expressed in the central nervous system that are hypothesized to contribute to this ability. I focus on human speech and birdsong and define the vocal learning subsystem of language as the experience-dependent modification of one’s vocal motor output with the goal of mimicking other members of one’s species (conspecifics) or of creating new sounds. Deafness in humans and experiments in animals teach us that vocal learners must hear and attend to the vocalizations of conspecifics (with some exceptions:Kroodsma et al., 1997;Leitner et al., 2002;Feher et al., 2009) and hear their own vocal output in order to produce effective vocal communication signals (for review seeDoupe and Kuhl 1999). Comparison of these sounds to evaluate the match sets the stage for those neural changes that enable adaptive modifications of vocal output. In humans, vocal learning drives the development of speech. Of course not all animals have been rigorously tested for the vocal learning ability. Tests of vocal learning often rely on deprivation of acoustic inputs during development and evaluation of how closely subsequent vocal output approximates normal song. One measure of how well song develops under these circumstances is whether it serves as an effective communication signal in conspecific interactions. Tests include: deafening early in development which prevents both hearing of others and of self; rearing in the absence of conspecific vocalizations which only prevents the former; and transient distortion of auditory feedback of the animal’s own Amylin (rat) vocal output, affecting only the latter. COL3A1 Non-invasive methods include determining whether changes in vocal output during normal development are more substantial than those expected due to physical maturation of the vocal apparatus (such as the larnyx;Fitch, 1997) or are uncharacteristic of the species-specific behavior. By a majority of these tests, passerine birds of the oscine suborder, known as songbirds, are vocal learners. In addition to humans and songbirds, the short list of animals demonstrated to possess this ability is confined to: parrots and hummingbirds which are in separate avian orders (raising the hypothesis that the trait emerged independently three times in the avian lineage); certain marine mammals including harbor seals, dolphins and cetaceous whales; elephants; and certain bat species. As outlined in the introduction to this volume (see contribution by Brenowitz, Perkel & Osterhout) songbird species such as canaries (Serinus canaria), white crowned sparrows (Zonotrichia leucophrys), Bengalese finches (Lonchura domestica, also known as society finches) and zebra finches (Taeniopygia guttata) have relatively short generation times and are amenable to laboratory life, making them extremely practical species in which to conduct controlled studies of the biological basis for vocal learning. In accordance with the general requirements for vocal learning outlined above, songbirds listen to the songs of their own species as well as their own vocal output (song perception), in order to adaptively modify control of the syrinx, or song organ, and the respiratory muscles used in singing. Experimental deprivation of these auditory inputs generally causes abnormal song in adulthood, but if temporarily applied and then removed, can extend the critical periods for song learning. This phenomenon is analogous to the extension of critical periods for neural organization in the visual system after rearing in darkness (for review seeHooks and Chen 2007). For example, young zebra finches deprived of tutoring during normal sensory.
This interaction connects FOXP2 with language disorders with which it was not otherwise implicated