eLife: The most detailed map of the brain's memory center reveals the mystery of connectivity

Australian scientists have created the most detailed map
of communication links between the hippocampus, the brain's memory control center, and the rest of the brain to date.
It may change the way we think about
human memory.

Dr Marshall Dalton, a researcher at the University of Sydney's School of Psychology, said: "We were surprised to find that there were fewer links between the hippocampus and frontal cortex regions, and more links to early visual processing areas than we expected
.
" "Still, it makes sense considering that the hippocampus plays an important role not only in memory, but also in imagination and our ability to construct mental images in our
minds.
"

The hippocampus is a complex structure similar to the hippocampus that hides deep within
the brain.
As an important part of the brain, it is very important for the formation of memories and plays a key role
in the transfer of memories from short-term storage to long-term storage.
But it also plays a role
in navigation, imagining imaginary or future experiences, creating mental imagery of scenes in the mind, and even visual perception and decision-making.

The team, led by Dr Dalton, which included Dr Arkiev D'souza of the Centre for Brain and Mind at the University of Sydney, Dr Jinglei Lv and Professor Fernando Calamante, relied on MRI scans in the neuroimaging database created for the Human Connectome Project (HCP), a research consortium
led by the National Institutes of Health.

They process existing HCP data
using custom technology they have developed.
This allowed them to trace connections in every corner of the brain all the way to the end point of the hippocampus — something that has never been done in the human brain
.

The most detailed map to date

"What we've done is taking a more detailed look at the white matter channels, which are essentially highways
of communication between different areas of the brain," Dr.
Dalton said.
"We developed a new method that allows us to map how the hippocampus connects to the mantle of the outer cortex of the brain, but in a very detailed way
.

"We have created a very detailed map
of white matter pathways that connect the hippocampus to the rest of the brain.
It is essentially a roadmap of brain regions directly connected to the hippocampus, supporting its important role
in memory formation.
”

Previous technical limitations inherent in NMR studies of the human hippocampus meant that their connections
could only be visualized on a very broad scale.
"But we have now developed a tailored method that allows us to confirm the location
of connections in different cortical regions in the hippocampus.
" This is unprecedented
in the human brain.
Dr.
Dalton said
.

Unexpected results

The team is pleased that their results are broadly consistent with data from past decades of overseas studies that rely on postmortem studies
of primate brains.
However, the University of Sydney team found that the number of connections between the hippocampus and some brain regions was either lower than expected (in the frontal cortex region) or higher than expected (in the visual processing region).

This may indicate that although some pathways have been conserved as humans evolved, the human brain may also have developed unique patterns
of connectivity that differ from other primates.
Further research is needed to tease out this
in more detail.

These differences in connectivity may just be one limitation of MRI technology — or they may be true
.
For example, they may help explain why some of our primate cousins—especially chimpanzees—do better than humans at certain memory tasks, especially those who rely on short-term memory
.
Chimpanzees outperform humans at cognitive tasks involving a form of mathematics known as game theory, which relies on short-term memory, pattern recognition, and rapid visual assessment
.

Dr.
Dalton mused, "While we have achieved high-resolution mapping of the human hippocampus, respiratory tracking methods on non-human primates, which can see things at the cellular level, are able to see more connections
than MRI can identify.
"

"It's also possible that the human hippocampus does have fewer connections to the frontal region than we expected, and a greater
number of connections to the visual region of the brain.
" As the new cerebral cortex expands, perhaps humans have evolved different patterns of connectivity to facilitate human-specific memory and visual functions, which in turn may cement human creativity
.

"It's kind of confusing — we just don't know
.
But we love the puzzles and will continue to investigate
.
”