Distributed Time-Domain Representations in the Birdsong System

The Birdsong System The forebrain pathways for song comprise three or more separate streams of information flow (reviewed by Mar-The ascending auditory system (green, Chicago, Illinois 60637 Figure 1) sends auditory input to HVc and NIf, and perhaps other song system nuclei, via a complex web of interconnections that starts with field L, the primary thal-amorecipient structure. The nuclei Uva, NIf, HVc, and Vocal communication systems are common throughout RA are connected sequentially and unidirectionally, the animal kingdom, and learned vocalizations such as forming a descending pathway for song production ulti-human speech or bird song are of particular interest. mately projecting to the brainstem hypoglossal nucleus, How are vocalizations represented in the brain? Neural which in turn projects to the avian vocal organ, the syrinx codes represent solutions to information-processing (red, Figure 1). Large bilateral lesions of Uva affect timing problems posed by an animal's behavioral require-of elements within song, and animals with large bilateral ments. In vocal communication, sounds are used as lesions of HVc and RA attempt to sing but fail to produce symbols, embodying certain parameters or features that songs. (The status of NIf in song production is uncertain.) have special significance for a given species. For exam-The anterior forebrain pathway (AFP) starts at the level ple, the song of male crickets will attract females, but of HVc and ultimately projects to RA (blue, Figure 1). only if it embodies certain species-specific characteris-Lesions of AFP nuclei have little effect on adult song tics. Physical attributes that affect sound transmission but severely disrupt the development of song (Bottjer through the acoustic habitat may affect the design of et al., 1984). (Logically, mMAN and DMP should be in-vocalizations, as in the case of long-distance communi-cluded in these pathways [see Figure 1], although the cation, but the use of symbols suggests a certain arbi-role of these nuclei in song development or song pro-trariness as to the parameters of the symbols. Addition-duction is unclear.) ally, where vocal communication is invoked as part of The two forebrain nuclei necessary for singing, HVc reproductive behavior, it evolves under sexual selection, and RA, have contrasting and complementary patterns which can favor solutions that are not optimal in the of connections: HVc receives multiple inputs and has engineering sense. The idiosyncratic, species-specific two outputs, whereas RA sends multiple outputs and features of bird songs—essential diagnostic tools for has two inputs (Figure 1). Another organizational feature …