Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Neuroscience

Supervisor

Scott MacDougall-Shackleton

Abstract

Song learning in songbirds typically happens during the first months after hatching, when the young bird is transitioning to sexual maturity and is more sensitive to extrinsic factors, such as acoustic experience, and intrinsic factors, such as changes in sex hormones. These factors influence the protracted song learning process that involves both behavioral changes at the song level and changes at the cellular level in the underlying neural structures of the vocal control system, the brain circuitry that allows song learning and production. However, the understanding of the neurogenic processes involved in the development of the vocal control system and its interaction with steroid hormones and acoustic experiences are still little explored. Thus, the goal of this thesis was to further understand the neurogenic processes such as cell proliferation, neuronal recruitment, neuronal maturation, and myelination that occur during the development of the vocal control system in male and female zebra finches (Taeniopygia guttata), as well as the effects that manipulating the acoustic environment and testosterone levels can cause. This research was divided in three projects: a description of the developing brain using different markers of neurogenesis and myelination (Chapter 2 & 3), a manipulation of acoustic experience (isolation and late tutoring) (Chapter 4), and a manipulation of testosterone during song development (Chapter 5). I found that there are sex-specific changes in neurogenesis and myelination over song development that differ between the posterior motor and anterior forebrain pathway of the vocal control circuit. Those sex differences emerged early and continued during the song learning process. Manipulations of the acoustic environment that delayed the sensitive period for song learning resulted in delays in neuronal recruitment and myelination during development. A premature increase in testosterone lead to a premature increase in myelination of the motor pathway. Testosterone had a stronger effect on myelination than on neuronal recruitment. Early acoustic deprivation of the tutor song delayed neuronal recruitment and myelination, and a premature increase in testosterone accelerated myelination. Thus, acoustic experience and sex steroid hormones are important for the neuronal development and myelination of this vocal control system that controls song learning and production.

Summary for Lay Audience

Song learning in songbirds typically happens during the first months after hatching, when the young bird is transitioning to sexual maturity and is more sensitive to extrinsic factors, such as acoustic experience, and intrinsic factors, such as changes in sex hormones. These factors influence the protracted song learning process that involves both behavioral changes at the song level and changes at the cellular level in the underlying neural structures of the vocal control system, the brain circuitry that allows song learning and production. However, the understanding of the neurogenic processes involved in the development of the vocal control system and its interaction with steroid hormones and acoustic experiences are still little explored. Thus, the goal of this thesis was to further understand the neurogenic processes such as cell proliferation, neuronal recruitment, neuronal maturation, and myelination that occur during the development of the vocal control system in male and female zebra finches (Taeniopygia guttata), as well as the effects that manipulating the acoustic environment and testosterone levels can cause. This research was divided in three projects: a description of the developing brain using different markers of neurogenesis and myelination (Chapter 2 & 3), a manipulation of acoustic experience (isolation and late tutoring) (Chapter 4), and a manipulation of testosterone during song development (Chapter 5). I found that there are sex-specific changes in neurogenesis and myelination over song development that differ between the posterior motor and anterior forebrain pathway of the vocal control circuit. Those sex differences emerged early and continued during the song learning process. Manipulations of the acoustic environment that delayed the sensitive period for song learning resulted in delays in neuronal recruitment and myelination during development. A premature increase in testosterone lead to a premature increase in myelination of the motor pathway. Testosterone had a stronger effect on myelination than on neuronal recruitment. Early acoustic deprivation of the tutor song delayed neuronal recruitment and myelination, and a premature increase in testosterone accelerated myelination. Thus, acoustic experience and sex steroid hormones are important for the neuronal development and myelination of this vocal control system that controls song learning and production.

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