Brain map clarifies neural connectivity behind motor function: study | Health

To address this problem, researchers at St. Jude Children’s Research Hospital developed a whole-brain atlas that describes the regions of the brain that transmit direct information to V1 interneurons, a type of cell necessary for movement. The resulting atlas and associated three-dimensional interactive website provide a foundation for learning about the physical landscape of the nervous system and how the brain communicates with the spine. The results were reported today in Neuron

“We have known for decades that the motor system is a distributed network, but that the end result passes through the spinal cord,” said corresponding author Jay Bikoff, PhD, Department of Developmental Neurobiology at St. Jude. “There you have motor neurons that cause muscle contraction, but the motor neurons do not act in isolation. Their activity is sculpted by networks of molecular and functionally diverse interneurons.”

Although enormous progress has been made in understanding the relationship between different regions of the brain and different facets of motor control, the precise way in which these regions connect to specific neurons in the spinal cord constitutes a blind spot in this area. Interneurons are difficult to study, mainly because there are hundreds of different and mixed varieties. Read also | How does the brain eliminate waste? Study takes a look inside

Study results:

“It’s like untangling a ball of Christmas lights, except it’s more difficult given that what we’re trying to untangle is the result of over 3 billion years of evolution,” said co-premier author Anand Kulkarni, PhD.

Recent advances have demonstrated the existence of molecularly and developmentally distinct interneuron subclasses, but much is still unknown about their place in neuronal communication. “Defining the cellular targets of descending motor systems is fundamental to understanding the neural control of movement and behavior,” Bikoff said. “We need to know how the brain communicates these signals.”

To dissect the circuits connecting the brain to the spinal cord, researchers used a genetically modified version of the rabies virus that lacks a key protein, the glycoprotein, on its surface. This inhibited the virus’s ability to spread between neurons.

This essentially blocked the virus at its origin. By reintroducing this glycoprotein into a specific population of interneurons, the virus could make a single jump across the synapses before becoming blocked again. The researchers used a fluorescent tag to track the virus. By tracking where the virus ends up, the researchers were able to identify which regions of the brain were connected to these interneurons. Read also | Your heart has its ‘own little brain’: Study reveals how the heart surprisingly works like the brain

The 3D map allows researchers to visualize the connections: The researchers applied this approach to a class of interneurons called V1 interneurons, which have previously been shown to play a critical role in shaping motor output. This work allowed them to precisely trace the origins of multiple signals received by these interneurons to the brain.

“We’re only targeting V1 interneurons, but it’s actually a very heterogeneous group of neurons. So we thought, ‘Let’s target as many V1 neurons as possible and see what projects to them,'” said Bikoff.

The researchers turned to two-photon serial tomography to visualize these neurons and generate a three-dimensional reference atlas. This technique reconstructs the brain by creating hundreds of micron-thick sections to reveal fluorescently labeled neurons. The atlas allowed researchers to make precise predictions about the network that connects different brain structures to the spinal cord and the interneurons with which they interact.

Identifying how these structures relate to the spinal cord allows researchers to study the neural circuits controlling movement in more depth, and the accompanying web atlas will ensure that the data is freely accessible to everyone. “We understand what some of the identified brain regions do from a behavioral perspective,” Bikoff explained, “but we can now hypothesize how these effects are mediated and what the role of V1 interneurons might be. This will be very useful in the field as a hypothesis generation engine.

Disclaimer: This article is provided for informational purposes only and is not a substitute for professional medical advice. Always seek the advice of your doctor with any questions you may have regarding a health problem.