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The Neurobiology of Social Reward

Conspecific vocalizations are special sounds. In some cases, animals will approach and even work to hear them; they have incentive salience. In female songbirds, the motivation to hear male song is dramatically altered by plasma levels of the reproductive hormone estradiol (E2). For example, female white-throated sparrows in non-breeding condition will press a key to hear male song several hundred times per day if they are treated with E2, whereas untreated females with low E2 are completely uninterested in hearing song. We published a number of papers looking at what E2 does in the brain to change the rewarding properties of social signals.

A female white-crowned sparrow responds to male song by performing a courtship display. 

Catecholaminergic axons (brown fibers) surround cells expressing the plasticity-associated protein Egr-1 (black) in the auditory forebrain of a female white-throated sparrow listening to male song.

Attending to a stimulus and assigning value to it both depend on monoamine neuromodulators such as dopamine and norepinephrine. Neurons containing these catecholamines serve as dynamic filters that integrate ascending sensory signals with environmental context and internal state, allowing behavioral responses to change accordingly. We have shown that E2 alters these systems; for example, E2 increases the density of catecholaminergic and serotonergic fibers innervating auditory areas. We have shown that E2 modulates the sound-induced release of these monoamines in auditory and reward areas.

Animal models are needed in order to understand autism and other human disorders of social reward. We are developing an assay to quantify social reward in zebra finches learning song. During the song learning period, juveniles are highly motivated to hear song and will peck a key to trigger song playback from a plastic model of an adult male (see video). This assay nicely models social interactions between parent and offspring and could be used to determine the effects of pharmacological manipulations on the reward value of those interactions. 

A juvenile zebra finch presses a key to hear male song from a plastic model of an adult.

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