Brain structure and function: a multidisciplinary pipeline to study hominoid brain evolution

To decipher the evolution of the hominoid brain and its functions, it is essential to conduct comparative studies in primates, including our closest living relatives. However, strong ethical concerns preclude in vivo neuroimaging of great apes. We propose a responsible and multidisciplinary alternative approach that links behavior to brain anatomy in non-human primates from diverse ecological backgrounds. The brains of primates observed in the wild or in captivity are extracted and fixed shortly after natural death, and then studied using advanced MRI neuroimaging and histology to reveal macro- and microstructures. By linking detailed neuroanatomy with observed behavior within and across primate species, our approach provides new perspectives on brain evolution. Combined with endocranial brain imprints extracted from computed tomographic scans of the skulls these data provide a framework for decoding evolutionary changes in hominin fossils. This approach is poised to become a key resource for investigating the evolution and functional differentiation of hominoid brains

Correction of magnetization transfer saturation maps optimized for 7T postmortem MRI of the brain

PurposeMagnetization transfer saturation (MTsat) is a useful marker to probe tissue macromolecular content and myelination in the brain. The increased B1+ inhomogeneity at 7T and significantly larger saturation pulse flip angles which are often used for postmortem studies exceed the limits where previous B1+correction methods are applicable. Here, we develop a calibration-based correction model and procedure, and validate and evaluate it in postmortem 7T data of whole chimpanzee brains.TheoryThe B1+ dependence of was investigated by varying the off-resonance saturation pulse flip angle. For the range of saturation pulse flip angles applied in typical experiments on postmortem tissue, the dependence was close to linear. A linear model with a single calibration constant C is proposed to correct bias in MTsat by mapping it to the reference value of the saturation pulse flip angle.MethodsMTsat was estimated voxel-wise in five postmortem chimpanzee brains. “Individual-based global parameters” were obtained by calculating the meanC within individual specimen brains and “group-based global parameters” by calculating the means of the individual-based global parameters across the five brains.ResultsThe linear calibration model described the data well, though C was not entirely independent of the underlying tissue and B1+. Individual-based correction parameters and a group-based global correction parameter (C=1.2) led to visible, quantifiable reductions of B1+-biases in high-resolution MTsat maps.ConclusionThe presented model and calibration approach effectively corrects for B1+inhomogeneities in postmortem 7T data