Pleasure seeking and birdsong

Abstract

Songbirds sing at high rates within multiple contexts, suggesting that they are highly motivated to communicate and that the act of singing itself may be rewarding. Little is known about the neural regulation of the motivation to communicate. Dopamine and opioid neuropeptides play a primary role in reward seeking and sensory pleasure. In songbirds, these neurochemicals are found within brain regions implicated in both motivation and reward, including the medial preoptic nucleus (mPOA) and ventral tegmental area (VTA). Several lines of research indicate that dopamine and opioids in these regions play a role in birdsong that differs depending upon whether song is used to attract females (female-directed song) or is not directed towards other individuals (undirected song). Evidence is reviewed supporting the hypotheses: (1) that distinct patterns of dopamine activity influence the motivation to produce undirected and female-directed song, (2) that undirected communication is intrinsically reinforced by immediate release of opioids induced by the act of singing, and (3) that directed communication is socially reinforced by opioids released as part of social interactions.

Figure 1

Data demonstrating a stimulatory role for dopamine and an inhibitory role for opioids in female-directed song. Mean measures of song produced by male starlings after vehicle treatment (open bars) and treatment (dark bars) with A) the D1 dopamine receptor antagonist SCH 23390, B) the dopamine reuptake inhibitor GBR-12909, C) the opioid receptor antagonist naloxone, and D) the mu opioid receptor agonist fentanyl. *Indicates p < 0.05. See text for additional detail. Figures redrawn from Riters et al. (2005) and Schroeder and Riters (2006).

Figure 2

Evidence that dopamine in mPOA and VTA is most closely related to female-directed song. Plots showing correlations between undirected (left) and female-directed (right) singing behavior and measures of tyrosine hydroxylase immunolabeling density in mPOA and VTA. Each point represents one individual. Presence of regression line indicates significant relationships (p < 0.05). See text for interpretation. Figures redrawn from Heimovics and Riters, 2008.

Figure 3

Evidence that opioids in mPOA and possibly VTA are most closely related to undirected song. Scatterplots illustrating relationships between male song production (mean arcsine transformed number of minutes at which each male was singing) and mENK fiber density in mPOA and VTA. Each dot represents data from a single male. Black dots represent data from males observed singing undirected song outside the breeding season. Gray dots represent males observed singing female-directed song during the breeding season. For each scatterplot, the R² and thick black regression line are for the regressions performed on data from males singing undirected and female-directed song combined. The thin dark gray line is the regression line for males singing female-directed song (mPOA: R² = 0.01, p = 0.80; VTA: R² = 0.20, p = 0.26). The light gray line is the regression line for males singing undirected song (mPOA: R² = 0.70, p = 0.009; VTA: R² = 0.53, p = 0.06). See text for additional detail. Figures redrawn from Riters et al. (2005).

Figure 4

Darkfield photomicrographs illustrating mENK fiber density in mPOA and the VTA of a male that did not sing and a male that sang at high rates. Arrows point to the boundaries of mPOA and VTA. TSM = tractus septomesencephalicus, v = ventricle, nIII = 3rd cranial nerve. Figure adapted from Riters et al. (2005).