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The most detailed map ever of the brain’s memory hub

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The hippocampus supports multiple cognitive functions, including episodic memory. It does so in coordination with other brain regions.

Australian scientists have created the most detailed map ever made of the communication links between the hippocampus and the rest of the brain. This map may change how we think about human memory.

Scientists generated this map using MRI scans from a neuroimaging database created for the Human Connectome Project (HCP), a research consortium led by the U.S. National Institutes of Health.

They used specialized methods they created to process the HCP data that was already available. This made it possible for them to do something that had never been done before in the human brain: track the connections from all parts of the brain to where they terminated in the hippocampus.

Dr. Marshall Dalton, a Research Fellow in the School of Psychology at the University of Sydney, said, “We were surprised to find fewer connections between the hippocampus and frontal cortical areas and more connections with early visual processing areas than we expected. Although, this makes sense considering the hippocampus plays an important role in memory and imagination and our ability to construct mental images in our mind’s eye.”

Graphic showing the hippocampus mapping process
Graphic showing the mapping process of the hippocampus undertaken by the University of Sydney team Credit: Marshall Dalton/ University of Sydney

“We’ve taken a much more detailed look at the white matter pathways, which are essentially the highways of communication between different brain areas. And we developed a new approach that allowed us to map how the hippocampus connects with the cortical mantle, the brain’s outer layer, but in a very detailed way.”

“We’ve created a highly detailed map of white matter pathways connecting the hippocampus with the rest of the brain. It’s a roadmap of brain regions that directly connect with the hippocampus and support its important role in memory formation.”

“Technical limitations inherent to previous MRI investigations of the human hippocampus meant it was only possible to visualize its connections in very broad terms. But we have now developed a tailored method that allows us to confirm where different cortical areas are connecting within the hippocampus. And that hasn’t been done before in a living human brain.”

The research team was thrilled to find that their findings largely supported findings from studies conducted abroad over the past couple of decades that had relied on post-mortem examinations of primate brains. The University of Sydney scientists discovered that, contrary to expectations, some brain regions’ connections with the hippocampus were substantially higher (in the case of visual processing regions) or much lower (in the case of frontal cortical areas).

This could indicate that although some pathways were conserved as humans evolved, human brains may also have developed unique connectivity patterns different from other primates. Further research is needed to tease this apart in more detail.

This could indicate that although some pathways were conserved as humans evolved, human brains may also have developed unique connectivity patterns different from other primates. Further research is needed to tease this apart in more detail.

Dr. Dalton said“Although we have achieved this high-resolution mapping of the human hippocampus, the tract-tracing method conducted on non-human primates – which can see down to the cellular level – can see more connections than can be discerned with an MRI.”

“Or it could be that the human hippocampus does have a smaller number of connections with frontal areas than we expect and greater connectivity with visual areas of the brain. As the neocortex expanded, perhaps humans evolved different connectivity patterns to facilitate human-specific memory and visualization functions which, in turn, may underpin human creativity.”

“It’s a bit of a puzzle – we just don’t know. But we love puzzles and will keep investigating.”

Journal Reference:

  1. Marshall A Dalton, Arkiev D’Souza, Jinglei Lv, Fernando Calamante. New insights into anatomical connectivity along the anterior-posterior axis of the human hippocampus using in vivo quantitative fibre tracking. eLife. DOI: 10.7554/eLife.76143 
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