September 2, 2009 Kamini Krishnan Tandra Toon

Article Focus Review of literature that combines use of functional or structural MRI and microelectrode techniques to macaque brains – allowing studies in macaque and humans to be linked. Purpose: Investigate neurophysiological connections involved in human cognitive function

Why Macaque Brains? Primates are closer to the human brain more than any other species. Nature 453, 833 (2008) fMRI in Macaques have “potential to link finding from human fMRI to those from macaque neurophysiology.”

Functional MRI Uses blood oxygenation level-dependent (BOLD) signals Records brain activity in real time during tasks Explores internal states and high level cognitive functions

Additional Techniques Used Microelectrode techniques Alone and combined with fMRI Structural MRI Sucal landmark Comparisons Cytoarchitectonics Neurophysiological and Microstimulation Diffusion Tensor MRI (DT-MRI) Caveat: Homologous regions are not necessarily functionally equivalent

Using fMRI in humans and Macaques – Comparative Studies Visual System Functional comparative tasks (e.g., passive viewing, 3D perception, Face perception, saccadic eye movements, shape processing) Similarities in visual areas are in “early visual areas” not necessarily in “higher visual areas” Higher Level Cognitive Functions Functional comparative tasks (e.g., cognitive set-shifting/cognitive flexibility)

fMRI comparison of Prefrontal Cortex Function PFC - Involved in executive functions (e.g., working memory, planning, response inhibition) Set-Shifting activation (cognitive flexibility) Areas of similarity from fMRI studies: caudal part of the inferior PFC Mirror neurons (neuronal activation during observation of an action performed by others) Areas of similarity include Brodmann’s Area 44 and 45 – implication for the theory of the evolution of language

fMRI comparison of Oculomotor-Control Networks Saccadic Eye Movements – neuronal network Variances noted between macaques and humans Areas of question include: Frontal Eye Field (BA 8 vs. BA 6); Intraparietal sulcus; Superior parietal lobule; Lateral bank of Intraparietal sulcus Need to further improve task designs 3D Perception Inter-species differences in functional architecture of the IPS Humans have four motion-sensitive regions; Macaques have one motion-sensitive area Conclusion: Human IPS contains areas for visuospatial processing – Macaques do not

Combination of MRI and microelectrode techniques Examines relationship between BOLD and neural signals Detect local and global brain activation patterns induced by microstimulation (e.g., for visual areas) Implications – Identify responsive brain regions to make appropriate decision for electrode-penetration sites

fMRI and combined Electrophysiology techniques Somatosensory system Primary and Secondary somatosensory cortices High-level vision in face perception Superior temporal sulcus Localizing Cortical Recording Sites Done during or just after a recording session; compliments existing localization methods that require post-mortem histology

Conclusion fMRI and MRI-based techniques – bridge gap between human imaging studies and macaque neurophysiological studies Direct comparison of functional brain structures Multi-dimensional analyses of functional connectivity Determines cortical recording sites

Questions and Discussion What high-level cognitive functions could be explored? What would be limited? What bias does the author have in publishing this article? What are the implications of these studies to further understand human evolution?