Structure and function of the social brain in primates

Thesis

Social abilities differ between primate species, with some thought to be specifically human, such as theory of mind (TOM). It has been argued that brain expansion and reorganisation throughout the primate evolutionary history has accompanied these differences (reviewed in chapter 1). In this thesis, we aimed to characterise how the primate social brain function and anatomy have evolved to shed light onto the evolutionary roots of the human social brain. We tackled this goal with a comparative approach and using magnetic resonance imaging (MRI). First, we designed a novel functional MRI experiment testing for the computational properties underlying TOM in the macaque brain in chapter 2. Our results showed that, as the temporo-parietal junction (TPJ) in humans, a middle superior temporal sulcus (midSTS) area in macaques can support TOM computations. We suggest that the macaque midSTS could have undergone reorganisation and specialisation as a precursor for the human TPJ. Then, in chapter 3, we investigated the architecture of the white matter temporal lobe underlying its cortical expansion and reorganisation from macaques to humans. By integrating several great ape species, we were able to suggest a stepwise evolutionary trajectory for the connectivity of the temporal lobe. We further characterised the evolution of primate brain organisation in chapter 4, by establishing a common methodology to study lemurs, squirrel monkeys and macaques. We identified a simian fronto-parietal and temporo-parietal elaboration in terms of cortical and connectivity expansion. In chapter 5, we set out to expand our understanding of the ontogeny of the macaque brain organisation by exploring the changes observed throughout their lifespan. We pinpointed a period in their early life where most of the changes occurs and revealed connectivity refinement throughout their life. Overall, this thesis suggests an evolutionary trajectory for the primate social brain (chapter 6) and paves the way for further investigation.

Authors: Roumazeilles, L

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: primates; social cognition; diffusion-weighted MRI; functional MRI; evolution; connectivity; neuroanatomy
• Subjects: Cognition; Comparative neurobiology; Primates; Brain