Date of Degree

9-2022

Document Type

Dissertation

Degree Name

Ph.D.

Program

Psychology

Advisor

Carolyn L. Pytte

Committee Members

Emily Jones

Patricia D'Ateno

Subject Categories

Experimental Analysis of Behavior | Neurosciences

Keywords

operant learning, adult neurogenesis, behavioral neuroscience, sex differences, brain lateralization, zebra finches

Abstract

Adult neurogenesis, the creation of new neurons, occurs throughout the lifespan in most organisms. However, though neuronal proliferation occurs daily, most of these neurons do not survive to become incorporated into preexisting neural circuitry and become fully functioning neurons. In the mammalian brain, adult neurogenesis occurs within the hippocampus, a brain region known to be important in learning and memory. In rats, successful acquisition of certain learning tasks increased new neuron numbers when the learning was sufficiently challenging (Curlik and Shors, 2011). It has also been demonstrated that a spatial discrimination task requires new neurons when the discrimination is more challenging (Clelland et al., 2009). In zebra finches, the caudomedial nidopallium (NCM) is a song system nucleus necessary for conspecific song discrimination learning and also receives new neurons (Chew, Vicario, and Nottebohm, 1996). The aim of this study was to examine the relationship between operant discrimination learning and adult neurogenesis in the songbird. We investigated the effects of two difficulty levels of an operant discrimination learning task on neuronal survival. We also evaluated whether any potential effects were sex-dependent. Thirty male and female zebra finches were trained in an operant Go/ No Go acoustic discrimination task using one of two pairs of conspecific song stimuli, one pair scored by acoustic software as very similar (the “Hard” discrimination task) and one pair scored by acoustic software as less similar (the “Easy” discrimination task). Corresponding matched control birds were exposed to identical acoustic stimuli but without operant consequences. Brain tissue was processed following learning task completion to quantify new cell numbers in NCM. Two-way repeated measures ANOVAs for each sex revealed that while males showed no differences in neuronal cell counts across difficulty levels when compared to their controls, female birds in the Hard training condition had more new neurons in both NCM hemispheres relative to female control birds in the Hard control condition, and there were no differences in NCM neuronal numbers between Easy training conditions and Easy control conditions when learning criterion of 80% correct responding was reached. New NCM neuron numbers did not correlate with mean number of trials to criterion in the learning task, but lateralization difference scores indicated that Hard training resulted in a left hemisphere shift, with a relative increase in new neuron numbers in left NCM as the result of Hard task training. These results extend the previous learning and neurogenesis research by showing that successful acquisition of a harder acoustic operant discrimination increases new neuron survival in female zebra finches as well as hemispheric alterations that suggest there is a relationship between left NCM function and operant learning.

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