Intrinsic Physiology and Experience-Dependent Plasticity of the Zebra Finch Caudal Mesopallium

Auditory processing is a complex task that relies on a hierarchical relay of information from the periphery to central regions of the nervous system. Intrinsic physiological properties of neurons in the auditory system allow it process spectrotemporal information for behavioral purposes such as sound localization and perception. Songbirds and humans hold parallels in the manner in which they use their auditory system for vocal communication. They both require early song and speech experience taught by a tutor to properly learn to sing or speak. Changes in the brain occur during these early life critical periods, which ultimately develop the neural circuitry for perceiving natural communication signals. In songbirds, the caudal mesopallium (CM) is a key auditory area in the learning and processing of conspecific vocalizations. In chapter 2, I investigate the intrinsic properties of neurons in CM to understand what physiological and morphological correlates give rise to its auditory processing capabilities. We found that neurons in CM have a diversity of firing patterns that are associated with various physiological and morphological correlates. Phasic-spiking neurons fire one or few action potentials to depolarizing stimuli, whereas tonic-spiking neurons fire sustained trains of action potentials. Phasic-spiking activity is regulated by a low-threshold, outward rectifying current. Phasic-spiking neurons are tuned to better follow rapid temporal modulations present in birdsong, whereas tonic-spiking neurons better entrain low frequency modulations, suggesting that intrinsic properties of CM neurons are specialized for processing specific auditory information. In chapter 3, I detail the experience-dependent transient emergence of phasic excitability during the song memorization phase of the sensory acquisition period of song learning. Depriving birds of normal colony-rearing experiences resulted in an abolishment of phasic responses during the age in which phasic excitability normally emerges in colony-reared birds. Phasic excitability was not able to be induced in birds that had been initially deprived of auditory experience, and passive membrane properties were altered even before phasic excitability normally emerges. The work presented in this dissertation lays the foundational groundwork for understanding the intrinsic neural correlates and plasticity of auditory perception in the songbird auditory system.