Evolutionary Specializations of Human and Chimpanzee Cortical Organization Open Access
Bryant, Katherine Louise (2015)
Abstract
Human brains are notable for their large neocortex, both in absolute size and relative to body size. Large brains are common to the hominoid lineage, but even when compared to our closest relatives -- chimpanzees and bonobos -- human brain size is exceptional. One of the longstanding questions in evolutionary neuroscience is whether the human brain expanded uniformly, or whether some neocortical regions expanded to a greater degree than others (reviewed in Schoenemann 2006). In other words, is the human brain simply an enlarged primate brain, or has neocortical reorganization accompanied of human brain expansion? To address this broad research question, I examine cortical organization in three ways. In the first chapter, I review and discuss the structure and function of the primate temporal lobe from an evolutionary perspective. This chapter will pay special attention to visual striate and extrastriate modifications. The second chapter covers the methodologies employed to examine the evolutionary modifications to human and chimpanzee visual cortex. Here, I detail immunohistochemical and diffusion tensor imaging methods used to examine human, chimpanzee, and macaque cortex. The results of these studies, which suggest modifications to striate and extrastriate, and multimodal temporal cortices in humans and chimpanzees, are detailed in the third chapter. The final chapter discusses the implications of these findings for understanding the evolutionary modifications to the temporal lobe that have occurred in the hominid lineage as well as specializations that have appeared in the human lineage since our divergence from our common ancestor with chimpanzees approximately 6 mya.
Table of Contents
List of Tables ii
List of Figures iii
List of Abbreviations iv
Introduction 2
1. Historical Background 8
A. Part 1 - Human Neocortex - A History of Science Perspective 10
B. Part 2 - Evidence for Ape and Human Specializations in Geniculostriate Projections from VGLUT2 Immunohistochemistry 20
C. Part 3 - Organization of Extrastriate Areas and Adjacent Temporal Cortex in Chimpanzees Compared to Humans and Macaques 25
D. Part 4 - Temporal Association Areas in Hominoids - Structure and Function 33
2. Methods 51
A. Part 1 - VGLUT2 Immunohistochemistry 52
B. Part 2 - Diffusion Tractography 56
3. Results 64
A. VGLUT2 Immunohistochemistry 65
B. Diffusion Tractography 68
4. Discussion 74
A. Part 1 - Evidence for Ape and Human Specializations in Geniculostriate Projections from VGLUT2 Immunohistochemistry 75
B. Part 2 - Organization of Extrastriate Areas and Adjacent Temporal Cortex in Chimpanzees Compared to Humans and Macaques 80
C. Part 3 - Methodological considerations for cortical mapping of temporal association areas in the human and hominoid lineage 95
Epilogue 112
Acknowledgments 127
References 128
Tables 151
Figures 154
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