Why do we all feel touch differently? | the edge

Neurobiologist Jerry Chen studies how different brain cells connect to form what he calls “circuit axes” that allow animals to use their senses, especially touch. Photo courtesy of Nicole Fuller Studios / Sayo

Neurology

New research from Boston University Neurobiologist Jerry Chen could help scientists better understand, for example, how to treat strokes and autism spectrum disorder.

When you touch something, whether you’re stepping on a sandy beach or touching a dog’s back, the sensations are transmitted to your brain. Feel the coarse grains of sand under your feet, the fluff of fur on your hand. But you also bring a little bit of yourself into feeling: Along with outside stimulation from the beach or a pup, there’s a memory of bygone moments — drying sand off your toes during summer vacation, cuddling with a family pet you miss so much. We all agree that something feels abrasive or soft, but we interpret that feeling a little differently.

“When we are aware of our environment, we are actually doing two things,” says Boston University neurobiologist Jerry Chen, an expert in cognitive function. “We take in all the senses, all the physical elements of the world; at the same time, we apply our own kinds of inference and subjective interpretation of what we think we perceive.”

In a new study published in ScienceChen illuminates that process, showing how the brain combines external information with internal memory to build a sense of touch. Looking at the brains of mice, Chen and a team of researchers from Boston University and the Allen Institute for Brain Science discovered a circuit in the primary somatosensory cortex — the part of the brain that receives signals related to touch, temperature, and pain — dedicated to computing tactile information. He says the circuit helps the brain know how to balance stimulation from outside the body with existing knowledge. The study may be important to our understanding of the range of neurological disorders and neuropsychiatric diseases that can alter sensory perception, from strokes to autism spectrum disorder. Improved knowledge of brain circuits may pave the way for more targeted therapies and interventions, says Chen, assistant professor of biology at Boston University’s College of Arts and Sciences.

Jerry Chen, assistant professor of biology in the College of Arts and Sciences, helped discover a “custom circuit made up of specific cells” that controls what happens when the brain receives sensory information. Jackie Ricciardi’s photo

As part of a dive into the workings of the brain, the team has developed a new method for scanning and monitoring cells: a platform that generates activity in the brain, shows the molecular makeup of cells on fire, and helps count all the data. This allowed Chen to look at how different neurons in the cerebral cortex interact and communicate when an animal touches something — and how those neurons adapt when something changes in the environment.

Chen and his team used the Allen Institute’s atlas of the mouse brain — a catalog of different types of brain cells — as a starting point for the project. Chen, a former Next Generation leader from the Allen Institute, says the atlas is great for identifying the location and class of neurons, but it doesn’t tell researchers much about the functions of neurons. His findings bring that detail and color. “It’s another level of understanding of how everything fits together,” says Chen, who is also an assistant professor of biomedical engineering at Boston College of Engineering. “The most important thing is that we linked the catalog to the functional definition – that would really open up a lot of ways for us to understand the brain.”

the edge He spoke with Chen about his findings and their potential to improve our knowledge and care of the brain.

s&a

with Jerry Chen

the edge: What do your results reveal?

Jerry Chen: When you perceive the world around you, your brain does a combination of processing the stimuli that make up the scene, but it also tries to fill in information based on what it has learned in the past to help you interpret what you are. sensor. For example, let’s say you’re looking through a bag and fumbling with your car keys. Your brain has learned how keys feel, so it is filling in information because you feel things of different materials or shapes to guide your search. However, there are times when you feel something, like a sharp edge, really jumping in and telling you that you’re on the right track and that you might have found your keys. Our findings essentially reveal that there is a dedicated circuit composed of specific cells in the catalog that we call axonal cells. These cells help alert the brain that you’ve encountered a salient feature that needs further investigation.

the edge: Did anything surprise you about those pivot cells?

Jerry Chen: Pivotal cells, which we have identified as important for feature detection, also respond in interesting ways when your environment changes. There is a certain set of genes known to be important for learning and adaptability which can go up or down depending on changing environments. We found that these genes are always turned on in axonal cells, which is inconsistent with some current principles. When environments change, these cells respond by trying to compensate for those changes.

the edge: What is the significance of your findings?

Jerry Chen: Our findings have relevance to a range of neurological disorders, such as stroke, and neuropsychiatric diseases, such as autism spectrum disorder, in which an individual’s sense of perception can be altered. Rather than viewing the brain as a homogeneous piece of tissue, understanding the specific cell types that are most relevant will allow us to develop highly targeted therapies.

This represents an exciting advance toward direct treatment of the underlying cause of a particular symptom, while avoiding unwanted side effects from other treatments and interventions. One of the big complications of treatments these days with brain disorders is that they not only affect the circuit of interest, but affect other circuits that you don’t necessarily want to mess with. The fact that we have a genetic knob on these specific circuits means that one can design targeted therapies that affect only those circuits.

the edge: I worked with the Allen Institute for Brain Science to apply a neuron catalog count to all types of cells in the brain. How was the catalog used in this study?

Jerry Chen: The catalog describes only the molecular structure of neurons, but does not necessarily say anything about the function of neurons or the calculations they perform. The technology my research team developed takes advantage of this new information from the catalog, and adds the next layer of information, the patterns of cell activity. It allows us to recognize and study the function of the cells in the index in a comprehensive way. That’s why we call it the comprehensive reading of activity and cell type MarKers, or CRACK, and it’s a pun on cracking neural circuits. We applied the CRACK platform to study a specific part of the cerebral cortex associated with our perception of touch. We looked at how different neurons from the index process information and talk to other neurons when an animal touches objects in its environment. We also looked at how neurons adapt when the environment changes.

Our CRACK technology will pave the way for Catalog 2.0, allowing researchers to collect molecular and functional information about all cells in the brain. People can start applying this platform to understand how different parts of the mouse brain work. We’re actually switching to a different part of the brain associated with sensory memory.

Our overall goal is to understand the human brain, so a lot of this cataloging that occurs in the mouse brain is really just a pilot for the ability to create a catalog similar to the human brain.

the edge: What made you want to study this issue?

Jerry Chen: Our laboratory is interested in studying the neural basis of perception and cognition. The brain is the most complex organ in the body. This complexity is partly determined by the fact that not all billions of neurons in the brain are alike. There are hundreds of thousands of different types of neurons, serving different functions and performing different computations. To really understand how the brain works, we need to break down the brain down to its individual components and then begin to question how these components interact during behavior.

the edge: What do you hope to study next?

Jerry Chen: There are a lot of directions we are going based on our new technology and our results. The idea of ​​circuits dedicated to the plasticity of neurons made up of particular cell types in the catalog—a surprising finding in our study—is a particularly intriguing one. This is one of the areas we pursue; We’re specifically looking at what types of circuits are potentially similar in other parts of the brain and how they function, during learning, memory and across time.

This research was supported by funding from the National Institutes of Health’s New Innovator Award, the Brain Research Through the Development of Innovative Neurotechnologies (BRAIN), and the National Institute of Mental Health.

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