The most detailed map ever made of the brain’s memory center has been created

It holds an enigmatic result regarding connectivity between the hippocampus and other parts of the brain.
Brittney Grimes
Image of the 'wiring diagram' of a human brain revealing connections to the hippocampus.
Image of the 'wiring diagram' of a human brain revealing connections to the hippocampus.

Marshall Dalton/ University of Sydney 

Researchers have created the most detailed map ever made of the human brain — specifically the communication links between the hippocampus. This part of the brain is the section that controls memory, particularly long-term and short-term memory, along with spatial memory, a type of memory that allows for the recollection of location. The research team consisted of scientists from the University of Sydney's Brain and Mind Center in Australia.

“What we've created is a highly detailed map of white matter pathways connecting the hippocampus with the rest of the brain. It's essentially a roadmap of brain regions that directly connect with the hippocampus and support its important role in memory formation,” said Dr. Marshall Dalton, a research fellow in the School of Psychology at the University of Sydney.

The results of the study were published in the journal eLife.

Fewer connections in the hippocampus

The researchers were surprised that there were fewer connections between the hippocampus and the frontal cortical areas, yet there were more connections than expected within the initial visual processing areas within the brain.

Dr. Dalton said there shouldn’t be a shock as to why there are more connections than expected in the visual processing area. “Although, this makes sense considering the hippocampus plays an important role not only in memory but also imagination and our ability to construct mental images in our mind's eye,” Dr. Dalton stated.

The hippocampus and its many functions

The hippocampus is at the base of the human brain located in the temporal lobe. It is an important component where memory is stored. It is a crucial part of the brain responsible not only for storing memories, but also for forming them. The hippocampus transfers memories from short-term to long-term storage in the brain as well.

It helps with navigation, creating and imagining future experiences and creating mental imagery of scene’s formed in the mind’s eye - imaging of recalled or imaginary scenes created in the mind.

The creation of the map

To create the map, the research team used MRI scans from a neuroimaging database created for the Human Connectome Project (HCP), a research group led by the U.S. National Institutes of Health.

The researchers — led by Dr. Dalton and included Dr. Arkiev D'Souza, Dr. Jinglei Lv and Professor Fernando Calamante from the University of Sydney's Brain and Mind Center —processed the HCP data using techniques they developed for the study. The methods they created allowed them to follow connections from all parts of the human brain, leading to the end points within the hippocampus. Creating the connections to form such a detailed map has never been done before in the human brain, the research team mentioned.

Most detailed map ever developed

Dr. Dalton described what he and his team looked for when they created the map, which is the most detailed map of the brain. “What we've done is take a much more detailed look at the white matter pathways, which are essentially the highways of communication between different areas of the brain,” said Dr. Dalton.

“And we developed a new approach that allowed us to map how the hippocampus connects with the cortical mantle, the outer layer of the brain, but in a very detailed way,” he continued. Previously, scientists could only envision the connections in the hippocampus due to technical limitations when MRI was used in the past for brain mapping.

The most detailed map ever made of the brain’s memory center has been created
Graphic showing the mapping process of hippocampus.

“But we have now developed a tailored method that allows us to confirm where within the hippocampus different cortical areas are connecting. And that hasn't been done before in a living human brain,” said Dr. Dalton.

Results from the study

The research team found that most of their results aligned with data from past studies, which relied on post-mortem studies of primate brains. However, there were key differences that pointed to connections within the brain. The team saw that the number of connections between the hippocampus and parts of the brain were either higher or lower than anticipated.

The differences could have either been from human brains developing patterns of connectivity different from other primates, or as noted by the team, it could have been a limitation of past MRI technique. Regardless, the researchers were puzzled by the smaller number of connections in the frontal areas of the brain and larger connections in the visual areas.

This map of the brain can help in the future diagnosis of degenerative diseases that affect memory, such as Alzheimer’s disease.



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