Nightly changes in neural activity and auditory processing of song control neurons depend on melatonin

Birdsong, as many complex behavioral patterns, needs to be acquired, maintained and adjusted throughout life. In songbirds, these tasks are held by a specialized neural network, the song control system. Nightly sleep has been shown to be highly relevant for the song learning and maintenance process. Distinct diurnal changes in neuronal activity can be observed in several song control areas expressing melatonin receptors, frequently in inhibitory interneurons. By disentangling the effect of melatonin from the confounding effects of sleep while continuously monitoring the activity of individual neurons in the song control system of freely moving adult male zebra finches for several days, we show a direct effect of melatonin on spontaneous as well as auditory evoked activity of song control neurons. We therefore suggest melatonin as an endocrine switch that enables night-time neural functions of song control neurons, crucial for formation and consolidation of song motor memory.