Serotonin and Song: neuronal and behavioral effects in the zebra finch

Abstract

Serotonin (5-HT) is a neuromodulator important in a vast array of neurological processes, including sensory and motor processing. Dysfunction of the 5-HT system is associated with depression and other clinically important mood disorders, and has been linked with learning deficits. Song production and song learning in the songbird provide a unique system for studying how the actions of neuromodulators on individual neurons combine to eventually change the dynamics of neural circuits, resulting in alterations of complex behaviors. The results described here are the first identification of a specific action of 5-HT in neurons of the song system in songbirds. I identify the receptors via which 5-HT act in a population of neurons crucial for song learning and production, and describe how 5-HT modulates excitability in these cells. I use in vivo electrophysiology combined with playback of the bird's own song to identify how 5-HT modulates network activity in these cells, and I use serotonergic lesions to connect the actions of 5-HT with a concrete change in a complex learned behavior- a decrease in the fundamental frequency of harmonic stacks in learned songs. These results show for the first time that 5-HT is involved in modulating spectral properties of song. My results follow an action of 5-HT from the level of individual receptors on specific neurons through to a change in a complex learned behavior. The conserved nature of the serotonergic system indicates the findings here are likely to generalize across vertebrates. This greater mechanistic understanding of particular actions of 5-HT on song production in songbirds will lead to improved knowledge of how 5-HT modulates neural activity underlying perception and behavior in mammals.