Scientists have created the most detailed map yet of the neural pathways that connect the memory bank of gray matter – the hippocampus – with the rest of the brain, revealing unexpected patterns of connections between regions.
“We were surprised to find fewer connections between the hippocampus and frontal cortex and more connections to early visual processing areas than we expected to see,” says University of Sydney psychologist Marshall Dalton.
While there is still much debate about the exact role of the hippocampus in memory, neuroscientists are confident that it plays a key role in building memory and integrating it into our perception to allow us to make decisions about the future.
A better understanding of how the hippocampus works in relation to other areas of the brain could one day help us deal with memory decline.
Using a new imaging technique called diffusion weighted imaging – a type of MRI that uses diffusion of water molecules through tissue to create contrast – Dalton and his colleagues created a high-resolution map of the connections between the hippocampus and cerebral cortex from the brains seven adult females under 35 years of age.
“We have now developed a custom method that allows us to confirm where within the hippocampus different cortical areas are connected. And this has never been done before in a living human brain,” says Dalton.
“What we’ve done is take a much more detailed look at the white matter pathways, which are essentially the communication highways between different areas of the brain.”
The researchers found that the hippocampus has different message networks, each connected to specific areas of the cortex. Our previous knowledge of these connections comes from dissections of primate brains, and the resulting brain map largely aligns with them.
However, the researchers found a much higher level of connections in the visual processing area of the human brain and fewer in the frontal cortex areas.
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Postmortem analysis performed in non-human primates can detect finer details at the cellular level, so we may simply not have been able to resolve all these connections in humans yet.
“Or it could be that the human hippocampus actually has fewer connections to frontal areas than we expect and more connectivity to visual areas of the brain,” Dalton explains.
“This makes sense, given that the hippocampus plays an important role not only in memory but also in imagination and our ability to construct mental images in our mind’s eye.”
Other recent studies have also found correlations between these brain regions. The team is curious to see if similar patterns are consistent across people of different demographics.
“As the neocortex expanded, perhaps humans evolved different patterns of connectivity to facilitate human-related memory and visualization functions, which, in turn, may support human creativity,” Dalton continues.
“It’s a bit of a puzzle – we just don’t know. But we like puzzles and we’ll keep investigating.”
This research was published in eLife.