The majority of us don't consider why we feel full after eating a huge holiday meal, or the reason we get coughy when we inhale smoke ...
The majority of us don't consider why we feel full after eating a huge holiday meal, or the reason we get coughy when we inhale smoke from a campfire or why we get sick at the same time after eating something toxic. The sensations that we experience are vital to our survival, but they tell us what our bodies are in dire need of at any given moment and allows us to quickly modify our behaviour.Physical sensations that are fundamental, referred to as inner senses occur in the brain as it takes in and interprets the information it receives from the internal organs. In the past, few studies have been dedicated to understanding the internal senses.
The basic biology behind internal organ sensing, which is an intricate cascade of intercellular communication between cells is now being more thoroughly understood by a group that is led by experts from Harvard Medical School.In a research study that was conducted by mice and published in Nature the team utilized high-resolution images to present the spatial patterns of how brain cells in the stem respond to inputs from organs in the internal.If the information is chemical or mechanical in the source, they found that the feedback of various organs triggers different clusters of neurons. These neurons clusters are connected to various organs and organ systems, are topographically arranged within the brain's stem. Furthermore, researchers have discovered that brain inhibition plays an essential role in enabling neurons to react to organs in particular.
The lead writer Chen Ran, a research associate in cells at HMS and HMS, stated, "Our study reveals the fundamental principles of how different internal organs are represented in the brain stem."
Understanding the way in which neurons and internal organs will require greater study. If the results are replicated in other species, like humans, they could allow researchers to develop more efficient treatment strategies for ailments caused due to internal sensing issues, for example, eating disorders as well as diabetes, hypertension lung conditions, and an the overactive bladder.According to the senior researcher Stephen Liberles, professor of cell biology at the Blavatnik Institute at HMS and a researcher at the Howard Hughes Medical Institute, "understanding how sensory inputs are encoded by the brain is one of the great mysteries of how the brain works." It has led to a better understanding regarding how sensory perception is created and how behaviors are generated through the brain.
Untutored and poorly studied
Researchers have been studying how the primary senses of smell, sight and taste, as well as hearing and even touch, which are used to navigate through the world, are created through the brain's processing of external data for more than 100 years. They've collected their findings in the course of time to reveal how the brain's sensory regions are arranged to interpret distinct stimulus.
In the early 1900s, for example, studies on the sensation of touch led researchers to develop the cortical homunculus that is part of the sensory system. The image below depicts cartoon-like body parts draped across the brain's surface and each one is aligned to the area in which it is processed, and then depicted in a scale that is in accordance with the sensitivity. David Hubel and Torsten Wiesel who are two professors from Harvard received a Nobel Prize in 1981 for their research on vision. They meticulously mapped visually-oriented brain regions, by studying the electric activity in neurons as they respond to stimuli in the form of visual. In 2004, a different pair of researchers won the Nobel Prize for their research in the olfactory pathway. They identified hundreds of olfactory sensory receptors and revealed exactly how the odor inputs are distributed in the brain and nose.
Up to the present, it's not clear how the brain processes and manages the feedback of organs in the body to regulate basic physiological processes like breathing and blood pressure, heart rate and nausea.
It is astonished that it has been so poorly studied and isn't fully known how the brain processes data from our bodies and interprets the signals as per Liberles.
"How the brain receives inputs from within the body and how it processes those inputs have been vastly understudied and poorly understood," Liberles says.
Internal organs, on the other hand, transmit information through hormonal forces, mechanical forces, nutrients, toxins, temperature and many more, all of which affects multiple organs, triggering various physiological reactions. Mechanical stretching, for example is a signal to flush whenever it is affecting the bladder, however, it signals satisfaction when it impacts the stomach. It triggers the reflex of stopping breathing when it is affecting the lungs.
A nerve cell group.
The nucleus in the solitary tract, also known as NTS is one of the parts of the brain stem Liberles Ran as well as their colleagues have focused on in their latest study.
The vagus nerve is believed to relay sensory information through internal organs to the NTS. Higher-order brain areas that manage the physiological processes and generate behavior take this information and transmit it to the brain. Therefore, the NTS is the brain's inner sensory gateway.
The two-photon imaging of calcium is a powerful method for monitoring the levels of calcium in brain neurons to provide a substitute for neural activity.
The researchers used this technique to test mice subjected to various types external organ stimulation. They utilized a microscope to observe the responses of a large number of neurons within the NTS simultaneously throughout the course of. The results illustrate neurons that are glowing throughout the NTS similar to starry night skies which blink in and out.
The traditional imaging techniques that include placing an electrode in order to capture a tiny number of neurons at one moment, "are like seeing only a couple pixels at a time," Ran stated.
"Our technique is like seeing all the pixels at once to reveal the entire image in high resolution."
The team observed that different areas of the body such as the stomach, or the larynx tend to stimulate different types of neuronal cells in the NTS. However researchers discovered a variety of instances in which mechanical or chemical stimuli to the same organ which usually trigger the same physiological response (like feeling full or coughing) stimulated neurons in the brain stem which were already in active. This suggests that specific neural networks could be devoted to represent different organs.
Researchers also discovered that the responses of the NTS were arranged as an image of space that they referred to as"the "visceral homunculus" as a comparison to the cortical homunculus, which was first discovered many years ago.
Finally, the researchers discovered that neurons must be turned off to allow signals to be transmitted across organs, to reach the brain stem. In the event that they used drugs to inhibit neurons, the cells located in the brain stem lost previous ability to select and began responding to different organs.
According to Ran the research findings lay the foundation in "systematically studying the coding of internal senses throughout the brain."
The foundations laid for the future
The results highlight many new questions, some of which the HMS team would like to tackle.
Ran is looking to find out what happens when the brain stem relays sensory information from the inside to brain regions of higher-order and triggers feelings that are associated with it, such as thirst and discomfort or hunger.
Liberles is keen to find out more about the molecular mechanism of the sensory system within our bodies. He's interested in finding out which organs' primary sensory receptors are in charge of detecting mechanical and chemical stimuli.
The structure of the system during the embryonic stage is a different subject that needs further investigation. Based on the latest research, it is crucial for researchers to examine the locations of neurons throughout the brain and their types.
To know how circuits are wired, and what different cell types do within the context of different circuits, he said that it was essential to study how various neuron types and their locations interrelate.
Liberles is particularly interested to find out if the results are applicable to humans and other animals. He noted that although several sensorimotor pathways can be shared among a variety of kinds of species, they have important evolutionary differences. Certain animals, for example aren't able to perform simple movements such as coughing or throwing up.
If the findings of the study can be confirmed in human beings it could help with the creation of more effective treatments for ailments that occur in the brain when the sensory system is compromised.
"Oftentimes these diseases occur because the brain receives abnormal feedback from internal organs," Ran says. "If we have a good idea of how these signals are differentially encoded in the brain, we may someday be able to figure out how to hijack this system and restore normal function."
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