University of Chicago, Illinois, USA
Songbirds are an attractive comparative model system for learning and memory sleep consolidation research. Songbirds are adept at solving perceptual problems such as song categorization. For example, European starlings exposed to new songs in an operant song categorization task rapidly establish new memories. Recall performance wanes throughout the first day of exposure but recovers after sleep and is more stable thereafter. Recall performance is sensitive to both retroactive and proactive interference, but only when interference arises from novel stimuli. Following initial memory consolidation, subsequent recall (reactivation) may make memories labile. These results replicate and extend similar results obtained in humans. Famously, songbirds also learn to sing. Both developmental song learning and adult song maintenance require auditory feedback, and exhibit sleep dependent learning. In young zebra finches, variability in singing and proximity to the auditory target (song "template") decreases throughout the day. These seemingly opposite patterns of effects for perceptual and sensorimotor learning emphasize that the effects of sleep consolidation depend on behavioral context. A compelling neuronal replay phenomenon gives further, mechanistic insight into sleep dependent song consolidation. Certain forebrain song system neurons that burst while driving daytime singing preferentially lose spikes in bursts over periods of sleep, which may be predicted in spontaneous "preplay" episodes of sleep bursting. The recent observation that syringeal EMGs also show replay during sleep allows for connecting these observations with a readout of whole animal behavior. The strong connection between neural activity and behavior is essential for directly testing theories of learning and memory consolidation.