Spatial Memory in Adult Male Rhesus Macaques: Relationshipbetween Season and the Influence of Testosterone Public

Abstract

Abstract Spatial Memory in Adult Male Rhesus Macaques: Relationship between Season and the Influence of Testosterone By Shannon Brooke Zoe Stephens Spatial memory research in humans and rodents generally find a sex difference favoring male performance on such tasks. One hypothesis for the observed male advantage is the influence of testosterone on spatial memory. Research investigating the activational and organizational effects of testosterone in rodents and humans has shown that testosterone can improve or enhance spatial abilities. Unlike the results in humans and rodents, results from a previous study in rhesus macaques suggest there is a female advantage on certain spatial tasks and testosterone had no impact on performance (Herman, 2006). The previous study in rhesus macaques tested males during the nonbreeding season, when testosterone levels were low. Using the methodology of Herman (2006), the current study examined male performance during the breeding season, when testosterone is elevated in order to further investigate the effects of testosterone on spatial task performance. Adult male rhesus macaques had been prenatally exposed to a control vehicle or flutamide, an androgen receptor blocker, either early or late in gestation. Results of the current study found a male advantage when only local cues were available and a female advantage on initial performance when only reliable spatial information was present. A positive correlation between testosterone and performance existed for control males when multiple cues were available, while a negative correlation was found when global cues were present in the absence of local cues. These correlations were not found in subjects receiving prenatal flutamide. In addition, control males' performance improved during the breeding season on a task requiring the use of local landmarks, while subjects receiving prenatal flutamide showed no improvement between seasons. Thus, the activational effects of testosterone are dependent on the strategies required to complete the task and these effects differ based on prenatal androgen exposure.

Table of Contents

Table of Contents Introduction ........................................................................................................................1

Spatial Memory in Nonhuman Primates ..........................................................................2 Sex Differences in Spatial Memory in Nonhuman Primates ...........................................5 Sex Differences in Spatial Memory in Rodents ...............................................................8 Sex Differences in Spatial Memory in Humans .............................................................10 Possible Explanations for Sex Differences in Spatial Memory .....................................14 Activational Effects of Testosterone on Spatial Cognition in Nonhuman Primates ......16 Activational Effects of Testosterone on Spatial Cognition in Rodents ..........................17 Activational Effects of Testosterone on Spatial Cognition in Humans..........................18 Organizational Effects of Testosterone on Spatial Cognition in Nonhuman Primates ..23 Organizational Effects of Testosterone on Spatial Cognition in Rodents ......................24 Organizational Effects of Testosterone on Spatial Cognition in Humans .....................26 Current Study .................................................................................................................28 Method ..............................................................................................................................30 Subjects ..........................................................................................................................30 Testing Facility ...............................................................................................................31 Training ..........................................................................................................................32 Testing Procedure ...........................................................................................................32 Data Collection ...............................................................................................................35 Hormonal Measures .......................................................................................................35 Statistical Analysis .........................................................................................................36 Results ...............................................................................................................................39 Breeding Season .............................................................................................................39 Seasonal Differences in Performance ............................................................................50 Sex Differences in Spatial Memory ...............................................................................56 Discussion..........................................................................................................................58 Sex Differences in Spatial Memory ...............................................................................58 Activational Effects of Testosterone on Spatial Memory ..............................................63 Organizational Effects of Testosterone on Spatial Memory ..........................................69 Conclusion ......................................................................................................................76

References .........................................................................................................................77 Tables ................................................................................................................................87 Figures ...............................................................................................................................98 List of Tables

Table 1. Calculations of Chance Scores (taken from Herman, 2006)........................87 Table 2. Mean Performance and Mean Percent Scores on the Spatial and Marker tasks Based on Testing Order during the Breeding Season.................................88 Table 3. Mean Performance and Mean Percent Scores on the First and Last Four Dual Cue Acquisition Trials for Male Rhesus Monkeys Tested during the Breeding Season by Prenatal Treatment............................................................89 Table 4. Pearson Correlations (one-tailed) of Testosterone and Performance or Percent Scores on the Three Tasks by Male Rhesus Monkeys Tested during the Breeding Season.......................................................................................90 Table 5. Seasonal Differences in Mean Performance and Mean Percent Scores of Male Rhesus Monkeys on the First Four Dual Cue Acquisition Trials by Prenatal Treatment....................................................................................91 Table 6. Seasonal Differences in Mean Performance and Mean Percent Scores of Male Rhesus Monkeys on the Last Four Dual Cue Acquisition Trials by Prenatal Treatment....................................................................................92 Table 7. Seasonal Differences in Working Memory Errors of Male Rhesus Monkeys by Prenatal Treatment..........................................................................93 Table 8. Seasonal Differences in Mean Performance Score of Male Rhesus Monkeys on the Four Spatial Trials by Prenatal Treatment..........................................94 Table 9. Seasonal Differences in Mean Percent Score of Male Rhesus Monkeys on the Four Spatial Trials by Prenatal Treatment...............................................95 Table 10. Seasonal Differences in Mean Performance Score of Male Rhesus Monkeys on the Four Marker Trials by Prenatal Treatment.........................................96 Table 11. Seasonal Differences in Mean Percent Score of Male Rhesus Monkeys on the Four Marker Trials by Prenatal Treatment.............................................97

List of Figures Figure 1

. The testing facility (view from the east side of the facility).......................99 Figure 2. A goal box used during the experiment.............................................100 Figure 3. Mean a) performance scores and b) percent scores during the breeding season on the four trials prior to the Spatial task and the Spatial task based on prenatal treatment...................................................................................101 Figure 4. Mean a) performance scores and b) percent scores during the breeding season on the trial prior to the Spatial task and the Spatial task based on prenatal treatment...................................................................................102 Figure 5. Mean a) performance scores and b) percent scores during the breeding season on the four trials prior to the Marker task and the Marker task based on prenatal treatment...................................................................................103 Figure 6. Mean a) performance and b) percent scores on the trial prior to the Marker task and the first Marker task trial based on prenatal treatment during the breeding season.......................................................................................104 Figure 7. Change in a) performance and b) percent scores over the four Marker task trials for each prenatal treatment group during the breeding season......................105 Figure 8. Perseveration a) performance and b) percent scores on the Marker task during the breeding season for each prenatal treatment......................................106 Figure 9. Mean a) performance and b) percent scores on the Spatial task during the breeding and nonbreeding seasons......................................................107 Figure 10. Mean a) performance and b) percent scores on the Marker task during the breeding and nonbreeding seasons......................................................108

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School	Laney Graduate School
Department	Psychology
Subfield / Discipline	Neuroscience and Animal Behavior
Degree	MA
Submission	Dissertation
Language	English
Research Field	Psychology, Psychobiology Psychology, Behavioral
Mot-clé	spatial memory testosterone Rhesus Macaque
Committee Chair / Thesis Advisor	Wallen, Kim, Emory University
Committee Members	Wolff, Phillip, Emory University Hampton, Robert, Emory University

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