Vocal Perception in Zebra Finches: Analysis of Measured Neural Responses to a Variety of Auditory Stimuli Using Neural Probe

Vocal communication plays a vital role in the social interactions of many species, including humans. Songbirds, due to their complex abilities in learning and producing vocalizations, are considered a suitable animal model for studying the neural basis of these behaviors. This thesis, as the first comprehensive research in Iran in the field of neuroethology of songbirds, addresses this subject. Initially, considering the novelty of this field branch in the country, a comprehensive literature review was conducted on the fundamentals of neuroscience, the brain structure of birds, song learning, and vocal communication, with a focus on the zebra finch as an animal model. Subsequently, the necessary tools and protocols for successful local field potential (LFP) and single-unit neural recording in zebra finches were developed and described. Then this system was validated through the successful replication of some previous findings. In this process, the Sharif neural probe, which was previously under development at the Department of Electrical Engineering at Sharif University of Technology, was tested and evaluated in this research, and its effectiveness in stable recording of LFP signals was confirmed. Then, utilizing this knowledge and these tools, the problem of hearing in noise in the context of vocal communication was studied. For this purpose, a novel and naturalistic experimental paradigm was designed in which the bird’s behavioral and neural responses to distance calls (a vocalization zebra finches use for communication when they are visually separated) were investigated in controlled acoustic backgrounds (colored noise and chorus noise). Behavioral results indicated that the birds were capable of discriminating calls in noise and adjusted their response strategy according to the perceived loudness of the sound. Neural recordings from projecting neurons in the HVC nucleus under anesthesia revealed a selective response of some of these neurons to distance calls and revealed the dependence of the intensity and latency of the neural response on the signal-to-noise ratio of the stimulus. Additionally, it was observed that response latency was greater in chorus noise, suggesting that this delay results from the increased complexity of the stimulus and can be interpreted as some sort of evidence accumulation. These findings are also discussed within the framework of viewing vocal communication as a form of perceptual decision-making, and strategies for the development of these studies are proposed.