Scientists Say: Connectome

A connectome is a map of nerve-cell connections in the brain

an illustration of a brain contains many small rainbow strands tangled around each other

The brain’s nerve cells, or neurons, constantly send messages to one another. They do this through long, wirelike structures called axons. Scientists can take images of axons bundled together to map neurons’ connections, as seen in this human brain image.

B. Marebwa and L. Bonilha/Medical University of South Carolina

Connectome (noun, “Kuh-NEK-tohm”)

A connectome is a map of connections between nerve cells, or neurons, in the brain. Neurons constantly exchange messages, which allows people and other animals to function.

The brain processes information through neurons talking to one another. Their messages travel through wirelike structures and the tiny connection points between cells.  

Neurons send each other messages in the form of chemicals. Typically, a neuron receives these chemical signals from its neighbors through small branches on its body called dendrites. The neuron then converts those chemical inputs into electrical signals. That electrical current then travels down the cell’s long tail, or axon. When it reaches the end of that axon, the electricity triggers the release of new chemicals. They relay the message on to the next neuron at a connection point called a synapse (SIH-naps).

Plotting out all these cellular links can reveal how the brain works. It can also show how health conditions such as ADHD or Alzheimer’s disease may be affecting the brain. This may lead to better treatments.

Scientists make connectomes by using different tools to peer inside brains. Powerful microscopes can zoom in on parts of individual cells. This has allowed scientists to pick out all the neurons and most synapses in some animals’ brains. But mapping all these cells and their connections is hard and takes a long time. That’s why it’s only been done for small, simple brains so far — like those of a fruit fly and some worms.

Brains the size of a human’s cannot be mapped down to the cellular level yet. So scientists are building connectomes that show the links between different regions in our brains. Each region contains neurons that help with certain types of tasks. The hippocampus, for instance, is a structure involved with memory. And the cerebellum helps with balance and coordination. To complete a task, such as remembering something, several brain regions will team up.

To figure out which regions are linked, scientists can use MRI scanners. These machines can peer into the brain from outside the body. This allows them to show axon pathways between neurons across different brain regions. They also can show which regions are active at the same time and likely work together. This is especially helpful when someone is doing a specific activity. The Human Connectome Project aims to map all such regional links in the human brain.

Scientists are mapping out the human brain’s nerve cell connections in a project called the Human Connectome Project. 

In a sentence

Scientists have built a connectome of all the neurons in the baby fruit fly brain.

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McKenzie Prillaman is the Spring 2023 science writing intern at Science News. She holds a bachelor’s degree in neuroscience with a minor in bioethics from the University of Virginia and a master’s degree in science communication from the University of California, Santa Cruz.

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