Abstract
The caudomedial nidopallium (NCM) is a telencephalic auditory area that is selectively activated by conspecific vocalizations in zebra finches and canaries. We recently demonstrated that temporal and spectral dynamics of auditory tuning in NCM differ between these species [1]. In order to determine whether these differences reflect recent experience, we exposed separate groups of each species and sex to different housing conditions. Adult birds were housed either in an aviary with conspecifics (NORM), with heterospecifics (canary subjects in a zebra finch aviary, and vice versa: (CROSS)), or in isolation (ISO) for 9 days prior to testing. We then recorded extracellular multi-unit electrophysiological responses to simple pure tone stimuli (250–5000 Hz) in awake birds from each group and analyzed auditory tuning width using methods from our earlier studies. Relative to NORM birds, tuning was narrower in CROSS birds, and wider in ISO birds. The trend was greater in canaries, especially females. The date of recording was also included as a covariate in ANCOVAs that analyzed a larger set of the canary data, including data from birds tested outside of the breeding season, and treated housing condition and sex as independent variables. These tests show that tuning width was narrower early in the year and broader later. This effect was most pronounced in CROSS males. The degree of the short-term neural plasticity described here differs across sexes and species, and may reflect differences in NCM's anatomical and functional organization related to species differences in song characteristics, adult plasticity and/or social factors. More generally, NCM tuning is labile and may be modulated by recent experience to reflect the auditory processing required for behavioral adaptation to the current acoustic, social or seasonal context.
Highlights
Songbirds learn their songs through a process of vocal imitation that has much in common with human speech acquisition [2]
In all avian species studied to date, including the two most commonly used in laboratory studies of birdsong neurobiology, the zebra finch (Taeniopygia guttata) and canary (Serinus canaria), the immediate early gene zenk is rapidly expressed in NCM in response to birdsong
A large difference exists between ISO males and females recorded during the spring (F = 146.7, p,0.0001, Figs. 2 and 3E and F). This sex difference in the ISO group during the spring contributes most to the sex by date by condition interaction. These findings demonstrate that NCM properties are not fixed in the adult bird: auditory tuning widths are influenced either by recent acoustic experience, social influences, or both, in canaries and zebra finches of both sexes
Summary
Songbirds learn their songs through a process of vocal imitation that has much in common with human speech acquisition [2]. Electrophysiological responses in NCM decrease following repeated presentation of a given stimulus, and vigorous responding occurs upon presentation of a novel song [12] This decreased responding to a particular sound (a form of stimulus-specific adaptation) persists longer for conspecific song stimuli than for heterospecific song and other auditory stimuli. This pattern of specificity suggests that NCM is specialized for discrimination and memory processes that could serve species and individual recognition, based on learned vocal communication signals. NCM sites in zebra finches are more broadly tuned and have more sustained responses than those in canaries [1] Such differences could underlie the selectivity for species-typical song found in ZENK and electrophysiological studies, and may reflect species differences in vocal repertoires. But not zebra finches, are seasonal breeders so we tested canaries from outside of the breeding season to assess the possible effects of reproductive status on tuning widths in that species, and found that tuning width increases from the spring to later in the year only in cross-housed males
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