Obviously, the human brain is incredibly complex, with about 100 billion neurons and an estimated 100 trillion connections. Even if you know the major areas of the brain, such as the cerebral cortex, cerebellum, hypothalamus, thalamus, forehead lobe, occipital lobe, temporal lobe, parietal lobe, amygdala, hippocampus, and medulla oblongata, you are still far from understanding how the brain is more deeply organized. which includes cellular, molecular and gene expression patterns and relationships.
Researchers at the Human Brain Project, a large research project with over 500 researchers from 123 institutions, work to understand the deep complexity of the human brain. With their specially built research infrastructure, they take neuroscience to the next level.
Specific cellular, molecular, and gene expression patterns in brain regions are linked to function, but their exact relationships remain largely unknown. New findings by researchers at the Human Brain Project (HBP) shed light on these relationships and enable a more comprehensive understanding of the organization of the human brain.
HBP researchers conducted a study that focused on three levels of cortical organization: cytoarchitecture, neurotransmitter receptor architecture, and neurotransmitter receptor gene expression. The study highlights the principles of human brain organization across the visual, auditory, somatosensory and motor functioning systems, and goes beyond the simplified view of a “mosaic” of areas that form the neocortex. The results were published in the journal NeuroImage.
To reveal the different properties of functional systems, and how brain areas within a functional system differ in terms of processing hierarchy – from primary to higher associative, the team analyzed cytoarchitectural and receptor architectural data from Julich Brain Atlas – a three-dimensional multimodal atlas of the human brain – and compared data with transcriptomic data from the Allen Human Brain Atlas.
“Bridging the gaps between different levels of brain organization is one of the biggest challenges in neuroscience today. In the Julich Brain Atlas, we can do it systematically. It integrates data and is an invaluable tool,” said Daniel Zachlod, first author of the study.
The researchers examined the relationship between neurotransmitter receptor densities and their corresponding genes in cytoarchitectural areas of the visual, auditory, somatosensory and motor systems. They analyzed differential gene expression within the brain regions in each of these functional systems.
“We found that the receptor architecture and gene expression patterns in a functional system change in a systematic way, corresponding to the increasing complexity of information processing,” explains HBP’s scientific director Katrin Amunts, who is the last author of the study.
The study shows a method for sorting out structure-function relationships by using the Julich-Brain Atlas on several levels to bridge the different scales of the brain.
Previous studies had already indicated the relevance of receptor gene expression for functional differentiation of the brain in rodents, but data on the human brain are much sparser and more fragmented. The authors of this study argue that it is mandatory to extend such studies to the human brain, in order to better understand the healthy brain, as well as the pathogenesis of brain diseases with changes in neurotransmitter systems.
Reference: “Combined analysis of cytoarchitectural, molecular and transcriptomic patterns reveals differences in the organization of the brain across human functional brain systems” by Daniel Zachlod, Sebastian Bludau, Sven Cichon, Nicola Palomero-Gallagher and Katrin Amunts, 19 May 2022, NeuroImage.
DOI: 10.1016 / j.neuroimage.2022.119286
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