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The Cognitive Effects of Naturally Occurring Domoic Acid Toxicosis in Wild California Sea Lions (Zalophus Californianus)

  • Author(s): Cook, Peter
  • Advisor(s): Wilson, Margaret
  • et al.
Abstract

This dissertation comprises three separate studies making use of a unique model for conducting cognitive neuroscience in a wild population: California sea lions (CSLs) (Zalophus californianus) undergoing rehabilitation for toxic exposure to algal metabolite domoic acid (DA). The approach described here presents some notable advantages over typical research with laboratory animals, featuring as it does large samples of big-brained, socially complex animals with broad genetic diversity and variable life histories. The first study assessed the feasibility of using an auditory habituation measure as a behavioral diagnostic assay for identifying CSLs with DA toxicosis in the rehabilitation setting--it was found that initial responsivity to repeated auditory tones was a strong predictor of post-hoc veterinary diagnoses. The second study replicated the behavioral findings of the first, but also added structural brain imaging, allowing quantitative correlation of test behavior to volumetric measures of hippocampal and parahippocampal regions. Regional brain volumes did not predict responsivity in this study, suggesting that the behavioral results were driven by some other neurological feature of DA toxicosis, likely epilepsy. The third study compared quantitative measurements of regional temporal lobe damage to performance in a delayed alternation task and a once-daily foraging task, the latter allowing both a measure of spatial working memory and long-term allocentric spatial memory. Right hippocampal formation volume predicted performance in all three measures. This suggests that DA toxicosis causes substantial impairments in hippocampal-dependent function, including working and spatial memory, and, further, that these cognitive mechanisms are at least partially lateralized to the right hippocampal formation. Results from these studies are used to argue for the value, both applied and theoretical, of naturalistic models for studying brain and behavior.

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