Forebrain circuits underlying the social modulation of vocal communication signals

Abstract

Across vertebrate species, signalers alter the structure of their communication signals based on the social context. For example, male Bengalese finches produce faster and more stereotyped songs when directing song to females (female-directed [FD] song) than when singing in isolation (undirected [UD] song), and such changes have been found to increase the attractiveness of a male's song. Despite the importance of such social influences, little is known about the mechanisms underlying the social modulation of communication signals. To this end, we analyzed differences in immediate early gene (EGR-1) expression when Bengalese finches produced FD or UD song. Relative to silent birds, EGR-1 expression was elevated in birds producing either FD or UD song throughout vocal control circuitry, including the interface nucleus of the nidopallium (NIf), HVC, the robust nucleus of the arcopallium (RA), Area X, and the lateral magnocellular nucleus of the anterior nidopallium (LMAN). Moreover, EGR-1 expression was higher in HVC, RA, Area X, and LMAN in males producing UD song than in males producing FD song, indicating that social context modulated EGR-1 expression in these areas. However, EGR-1 expression was not significantly different between males producing FD or UD song in NIf, the primary vocal motor input into HVC, suggesting that context-dependent changes could arise de novo in HVC. The pattern of context-dependent differences in EGR-1 expression in the Bengalese finch was highly similar to that in the zebra finch and suggests that social context affects song structure by modulating activity throughout vocal control nuclei.

Dissociable Effects on Birdsong of Androgen Signaling in Cortex-Like Brain Regions of Canaries

“…We measured syllable sequence variability by methods similar to others (Nottebohm et al, 1986;Sakata et al, 2008;Matheson et al, 2016). We analyzed for each bird transitions from its dominant (i.e., most frequently used) syllable type to all other types.…”

“…These types of transitions are considered to be fully stereotyped sequences (e.g., similar to motifs in zebra finch songs). For these situations, we treated the transitions from these stereotyped sequences as "branch points" (e.g., in the fully stereotyped sequence A-B, the transitions from B were used for calculating first order entropy) as done in previous studies (Sakata et al, 2008;Hampton et al, 2009;Tchernichovski and Marcus, 2014;Matheson et al, 2016). There was no effect of treatment on the presence of dominant syllable types that were defined as branch points.…”

“…The sensorimotor phase starts with a period of quiet variable vocalizations labeled subsong (akin to babbling) followed by periods of highly variable song with adult elements called plastic song that culminates in stable crystallized song. Experiments in sparrows demonstrated that this process of moving from variable song to stable crystallized song is dependent on T (Marler et al, 1988). Castrated male sparrows failed to transition out of the plastic song state, whereas treatment with T induced crystallization; in some birds the T implant was removed and the birds returned to a state of plastic song (Marler et al, 1988).…”

“…Experiments in sparrows demonstrated that this process of moving from variable song to stable crystallized song is dependent on T (Marler et al, 1988). Castrated male sparrows failed to transition out of the plastic song state, whereas treatment with T induced crystallization; in some birds the T implant was removed and the birds returned to a state of plastic song (Marler et al, 1988). Some seasonally breeding songbirds such as male canaries (Serinus canaria) additionally undergo substantial changes in vocal stability as adults: during the fall (i.e., nonbreeding season) when T concentrations are low, they repeat the sensorimotor phase, and can produce a new crystallized song during the spring (i.e., breeding season) when T concentrations are high (Nottebohm et al, 1986).…”

Aromatase inhibition rapidly affects in a reversible manner distinct features of birdsong

“…The stereotypy of bandwidth was computed using the coefficient of variation (CV) (CV = (SD/AVG)*100)); the higher the CV of song bandwidth, the lower the stereotypy of said. CV of acoustic variables has been used in previous studies as measures of song stereotypy141546596263.…”