DELAY DISCOUNTING, SOCIAL BEHAVIOR, AND MORPHOLOGICAL DEVELOPMENT IN ADOLESCENT RHESUS MACAQUES
Publisher
The University of Arizona.Rights
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.Abstract
Adolescence in human and non-human primates marks a developmental period of significant change in brain structure and function. One point of interest for the adolescent period lies with the shift from the amygdala to the prefrontal cortex (PFC) as the predominating brain region for reward processing throughout adolescence. The amygdala determines the emotional salience of reward and is associated with impulsive behaviors, which are heightened during adolescence across primate species. The PFC is associated with cognitive control and inhibition of impulsivity in the interest of future planning. In this project, we assessed the reward processing of four adolescent rhesus macaques (Macaca mulatta) through a Delay Discounting Task where the four monkey subjects (A, B, C, P) chose between a low value immediate reward of one food pellet and a high value delayed reward of three food pellets. We found that the Indifference Points, where the monkeys valued equally the two options, were shorter when the delay change was decreasing compared to increasing. However, the Indifference Points were not significantly affected by testing the animals first with increasing and decreasing delays. Another point of interest for the adolescent period is the development of prosocial behavior and interaction within social groups. Primates have complex social hierarchies that give preference to prosocial behaviors that increase chance of survival and provide companionship. Relationships between individuals can be categorized into agonistic (aggressive) and affiliative behaviors that define their interactions and role as group members. Three monkeys (B, C, P) significantly expressed more aggressive behaviors as the monkey watching the task than as the task monkey. Two monkeys (B, P) significantly expressed more affiliative behaviors as the other monkey than as the task monkey. All four monkeys significantly expressed more aggressive behaviors than affiliative, regardless of their role. The same four monkeys performed a Social Task in pairs of two (A and B, C and P), where one actor monkey made choices for themselves and for their social partner. The actor monkey chose whether a food pellet was given to both monkeys or only themself (self-both); the actor monkey also chose whether a food pellet was given to the other monkey or to nobody (other-neither). We created a Preference Index where zero means the subject had no preference, positive values are more other-preferring, and negative values are more self-preferring. Significant positive other-preference was shown for all four monkeys in the self-both condition. In the other-neither condition, monkeys A and C were significantly other preferring, monkey B was significantly neither-preferring, and monkey P showed no preference. Morphometric measurements were taken monthly to monitor their anatomical and hormonal development throughout puberty. We used body weight, testicular volume, and testosterone level as our metrics.Type
Electronic thesistext
Degree Name
B.S.Degree Level
bachelorsDegree Program
Neuroscience and Cognitive ScienceHonors College