Abstract
Songbirds are an excellent model for investigating the perception of learned complex acoustic communication signals. Male European starlings (Sturnus vulgaris) sing throughout the year distinct types of song that bear either social or individual information. Although the relative importance of social and individual information changes seasonally, evidence of functional seasonal changes in neural response to these songs remains elusive. We thus decided to use in vivo functional magnetic resonance imaging (fMRI) to examine auditory responses of male starlings that were exposed to songs that convey different levels of information (species-specific and group identity or individual identity), both during (when mate recognition is particularly important) and outside the breeding season (when group recognition is particularly important). We report three main findings: (1) the auditory area caudomedial nidopallium (NCM), an auditory region that is analogous to the mammalian auditory cortex, is clearly involved in the processing/categorization of conspecific songs; (2) season-related change in differential song processing is limited to a caudal part of NCM; in the more rostral parts, songs bearing individual information induce higher BOLD responses than songs bearing species and group information, regardless of the season; (3) the differentiation between songs bearing species and group information and songs bearing individual information seems to be biased toward the right hemisphere. This study provides evidence that auditory processing of behaviorally-relevant (conspecific) communication signals changes seasonally, even when the spectro-temporal properties of these signals do not change.
Highlights
Birdsong, like human speech, is a learned vocal behavior whose function is to communicate with others
Starlings that could hear but not interact with adults during early life are unable to differentiate individual whistles and warbling motifs in their vocalizations and in their neural (NCM) responses to these songs, independently of the structural differences between these two types of songs. They do produce individual whistles and warbling motifs whose acoustic morphology is species-typical, these songs are not produced in species-typical sequences and caudomedial nidopallium (NCM) responses to these songs do not differ like they normally differ in wild-caught starlings (George et al, 2008)
Each functional magnetic resonance imaging (fMRI) experiment consisted of two sessions in which auditory responses in the brain were measured to the presentation of either songs conveying species-specific and group information (SPEC session) or individual information (INDIV session), and synthetic pure tones (PT, both sessions)
Summary
Like human speech, is a learned vocal behavior whose function is to communicate with others. It is a signal that has a sender and a receiver and whose meaning and function is asserted by the effect on the receiver and by the signal’s structure (see review by Scott-Phillips, 2008). In cowbirds (Molothrus ater ater) for example, the same song types may elicit either aggression in males or attraction in females (West et al, 1997). In the European starling (Sturnus vulgaris), the high-pitched trills that characterize male song sequences during the breeding season have been observed to be involved in female attraction during the breeding season. The neural response to these trills in female starlings’ primary auditory area is higher during the breeding season than during the non-breeding season (Cousillas et al, 2013)
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