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Project

Whole brain mesoscale functional imaging in macaques

The macaque monkey model is widely used for neuroscience studies, as it allows researchers to use invasive tools to systematically study the brain. In addition, the macaque brain is anatomically and physiologically more similar to the human brain than other animals used in research. However, due to the small size of the macaque brain, higher spatial resolution imaging is required to obtain the same level of structural detail in the macaque as in the human brain. The objective of this thesis was to develop high-resolution (f)MRI in monkeys and gain more insight into the primate visual system.

To achieve this goal, in Chapter 2, we combined implanted phased array coils, contrast agents, and state-of-the-art image acquisition sequences and data analysis tools, to achieve 0.6 mm isotropic resolution fMRI in awake monkeys covering nearly the entire brain and using conventional clinical 3T scanners. As a proof-of-concept, we mapped segregated color-selective thin and disparity-selective thick stripes of monkey V2 with high intra- and inter-subject reproducibility. In addition, using 0.4 mm isotropic resolution MRI for myelination mapping, we showed that the pale stripes contain a higher density of myelination compared to the thick and thin stripes. These findings are particularly interesting because they pave the way for large-scale mesoscale functional and structural imaging of the entire cortex in macaques.

We then investigated the fine-grained functional organization of the macaque visual cortex and uncovered several novel findings. In Chapter 3, by adding high-resolution myelination mapping data to high-resolution retinotopic mapping data, we confirmed that, contrary to prevailing views, the retinotopic organization of dorsal cortex immediately rostral to V2d differs substantially from the textbook models, but is remarkably similar to that proposed for New World monkeys.

In Chapter 4, we mapped the whole-brain visual scene processing system in macaques and revealed a much more complex and extensive scene processing system, surprisingly elaborated in frontal cortex. Both resting-state functional connectivity and functionally relevant network analyses showed that all the core scene-selective patches, including the frontal patches which were previously not identified, are tightly interconnected, forming a scene-processing network. Furthermore, this scene-processing network is largely dissociated from both the body- and face-processing networks.

In Chapter 5, we mapped the microarchitecture of category-selective areas in the ventral stream and found that established face- and body-selective areas consist of functional mesoscale units that can be distinguished on the basis of functional criteria and distinct interhemispheric functional connectivity. Surprisingly, similar neuronal clusters emerged from single cell responses recorded from the same fMRI-defined body patch, suggesting that category-selective patches contain functionally heterogeneous neurons and that cells with similar responses are spatially clustered, forming mesoscale structures that mimic functional columnar structures observed in early visual cortex.

In conclusion, the results of this thesis illustrate the potential value of high-resolution macaque MRI. We have shown that at submillimeter resolution, (f)MRI is capable of reliably detecting fine-scale functional and anatomical structures at near-columnar resolution in macaque monkeys. As a result, the mesoscale functional organization of the vast, uncharted territory of the brain, which is difficult to access with traditional invasive techniques, can now be studied in detail.

Date:1 Nov 2014 →  3 May 2023
Keywords:MRI, non-human primate, visual cortex
Disciplines:Neurosciences, Biological and physiological psychology, Cognitive science and intelligent systems, Developmental psychology and ageing
Project type:PhD project