Category: NeuroScience

In this feature, we discuss six studies that uncover new and unexpected truths about the organ we hold in our skulls. Neuroscience is never easy, but the resulting intrigue is worth the effort.

The brain is the pivotal hub of our central nervous system. Through this organ, we take note of the world, we assess our version of reality, we dream, we ponder, we laugh.

Its nervous tendrils permeate every inch of our bodies, innervating, controlling, and monitoring all that we touch, think, and feel.

Its other, more silent, yet vital role is its command over our survival as an organism — our heartbeat, our breathing rate, the release of hormones, and much more.

Because of its vast complexity, it is no surprise that we continuously learn new things about the brain.

In this feature, we will discuss some recent research that shines fresh light on the organ that defines us as individuals, controls our emotions, and retains detailed information about our first pet.

To start, we will take a look at links between the brain and a seemingly unrelated part of the body — the gut.

Brain and gut
At first glance, it seems surprising that our brain and gut are interlinked, but we have all experienced their tight relationship. By way of example, many of us, when especially hungry, might be more easily enraged.

In fact, there is a great deal of neural conversation between the gut and the brain. After all, if the gut is not well fed, it could be a matter of life and death; the brain needs to be informed when energy is low so that it can call other systems into action.

1. Sugar may alter brain chemistry after only 12 days
Recently, Medical News Today published a study that investigated how sugar influenced the brain of a particular breed of swine, known as Göttingen minipigs. For 1 hour each day for 12 days, the pigs had access to sucrose solution.

Before and after the 12-day sugar intervention, the scientists used a PET imaging technique that measured dopamine and opioid activity. They also imaged five of the pigs’ brains after their first sucrose experience.

They chose to focus on the dopamine and opioid systems because both play pivotal roles in pleasure seeking behavior and addiction. One of the authors, Michael Winterdahl, explains what they found:

“After just 12 days of sugar intake, we could see major changes in the brain’s dopamine and opioid systems. In fact, the opioid system, which is that part of the brain’s chemistry that is associated with well-being and pleasure, was already activated after the very first intake.”

The authors published their findings in the journal Scientific Reports. Scientists have debated whether sugar is addictive for decades, but these findings, as the authors explain, suggest that “foods high in sucrose influence brain reward circuitry in ways similar to those observed when addictive drugs are consumed.”

2. Gut bacteria and the brain
Over recent years, gut bacteria and the microbiome at large have become increasingly popular with scientists and laypeople alike. It is no surprise that gut bacteria can influence gut health, but it does come as more of an eye-opener that they might influence our brain and behavior.

Although at first, this idea was a fringe topic, it is now moving closer to the mainstream. However, links between gut bacteria and mental health are still relatively controversial.

Recently, a study appearing in Nature Microbiology utilized data from the Flemish Gut Flora Project, which included 1,070 participants. The scientists wanted to understand whether there might be a relationship between gut flora and depression.

As the researchers hypothesized, they did find distinct differences in the gut bacterial populations of those with depression when they compared them with those who did not experience depression.

These differences remained significant even after they had adjusted the data to account for antidepressant medication, which might also influence gut bacteria.

However, as the authors note, there is still the chance that factors other than depression might have driven the correlation. Before they firm up the links between gut bacteria and mental health, scientists will need to carry out much more work.

MNT published an in-depth article on how gut bacteria might influence the brain and behavior here.

3. Parkinson’s and the gut
Perhaps now that we have established a connection between the gut and the brain, we will find the thought of a gut link to Parkinson’s disease less surprising. MNT covered a study that looked at this theory in 2019.

Misfolded alpha-synuclein is the primary hallmark of Parkinson’s disease. These proteins aggregate and destroy certain dopamine producing cells in the brain, causing tremor and the other symptoms of the disease.

The study, in the journal Neuron, explains how the researchers created a model of Parkinson’s disease by injecting alpha-synuclein fibrils into muscles in the mice’s gut.

In the experiment, these clumps traveled from the gut to the brain through the vagus nerve. Within a few months, the mice developed symptoms that mirrored Parkinson’s in humans.

Following on from the findings above, some researchers have begun asking whether prebiotics might stave off Parkinson’s. A study using a roundworm model suggests that this theory might be worth pursuing.

Discoveries and mysteries
Of course, because the brain is complex, it still holds many secrets. Even some of the most common behaviors, as yet, defy a neuroscientific explanation. A good example is a humble yawn.

Yawning is part of the human experience, but no one knows quite why we do it.

4. A yawning chasm in our knowledge
Scientists have roundly dismissed conventional theories, such as a lack of oxygen in the brain. Why we do it, and what is happening in the brain is unclear. One of the particularly curious things about yawning is the fact that it is contagious.

A recent study investigating the contagious power of yawns appeared in the journal Current Biology. The authors believe that primitive reflexes in the primary motor cortex might trigger yawn contagion.

To investigate, the scientists used transcranial magnetic stimulation (TMS), which is a noninvasive technique employing magnetic fields to stimulate nerve cells. The researchers showed participants videos of people yawning and asked them to either resist the yawn or to let it out.

They found that when they increased levels of excitability in the motor cortex, they also increased participants’ urge to yawn.

As part of the experiment, the researchers measured levels of excitability in participants’ brains without TMS. They found that individuals with higher levels of cortical excitability and physiological inhibition in the primary motor cortex were more predisposed to yawn.

This finding adds evidence in support of one theory about yawning that involves the mirror-neuron system. This system, as the authors explain, “is thought to play a key role in action understanding, empathy, and the synchronization of group social behavior.”

So, we still do not fully understand yawning, but we are gathering evidence, and it might involve empathy.

5. New neurons in old age
Neurogenesis — or the creation of new neurons — is almost entirely complete by the time a newborn greets the world. Although new neurons may emerge in some parts of the brain during adulthood, for the majority of the brain, we have to make do with the neurons we get when we are born.

A study from 1998 claimed to have demonstrated that neurogenesis took place in the hippocampus, a region of the brain that is particularly important for memory. The findings were controversial, and later studies were contradictory.

Moving forward 2 decades, another team of scientists decided to settle the debate with the largest sample of brain tissue to date; they published these new findings in the journal Nature Medicine.

The team focused on a part of the hippocampus called the dentate gyrus. Incredibly, the researchers found that neurogenesis was occurring in all the samples of brain tissue, even in samples from individuals in their 90s.

The authors note that neurogenesis appears to slow as we age, but that it continues throughout our lives.

As with so many areas of neuroscience, however, researchers now need to gather more evidence as other studies have failed to replicate the findings.

6. A new type of brain cell
Even now, we are identifying new types of cells in the brain. A paper in Nature Neuroscience introduced one such newcomer to the neuroscientific lexicon: the rosehip neuron.

Rosehip neurons are inhibitory neurons, which are a class of cells that reduce the activity of other neurons. In the case of rosehip neurons, they apply the brakes to neurons in a way subtly different from other, similar cells.

In particular, rosehip neurons influence the activity of cortical pyramidal neurons, which account for around two-thirds of all neurons in the mammalian cerebral cortex.

Because scientists have not seen this cell in mice or other commonly used laboratory animals, the researchers believe it might help us understand why the human brain is so unique. However, at this stage, this is conjecture, and it is still not clear exactly what rosehip neurons do.

Of course, the studies this article discusses barely scratch the surface of neuroscience research today. Although we do not know what the future holds, we can guarantee it will be exciting.

It’s Brain Awareness Week, and to mark the occasion, we’re taking a look at research focused on the most complex organ in the human body. You can view all of our content for Brain Awareness.

Source: https://www.medicalnewstoday.com/articles/neuroscience-research-6-fascinating-findings#Discoveries-and-mysteries

Neurons that store abstract representations of past experiences are activated when a new, similar event takes place.

Imagine you are meeting a friend for dinner at a new restaurant. You may try dishes you haven’t had before, and your surroundings will be completely new to you. However, your brain knows that you have had similar experiences — perusing a menu, ordering appetizers, and splurging on dessert are all things that you have probably done when dining out.

MIT neuroscientists have now identified populations of cells that encode each of these distinctive segments of an overall experience. These chunks of memory, stored in the hippocampus, are activated whenever a similar type of experience takes place, and are distinct from the neural code that stores detailed memories of a specific location.

The researchers believe that this kind of “event code,” which they discovered in a study of mice, may help the brain interpret novel situations and learn new information by using the same cells to represent similar experiences.

“When you encounter something new, there are some really new and notable stimuli, but you already know quite a bit about that particular experience, because it’s a similar kind of experience to what you have already had before,” says Susumu Tonegawa, a professor of biology and neuroscience at the RIKEN-MIT Laboratory of Neural Circuit Genetics at MIT’s Picower Institute for Learning and Memory.

Tonegawa is the senior author of the study, which appears today in Nature Neuroscience. Chen Sun, an MIT graduate student, is the lead author of the paper. New York University graduate student Wannan Yang and Picower Institute technical associate Jared Martin are also authors of the paper.

Encoding abstraction

It is well-established that certain cells in the brain’s hippocampus are specialized to store memories of specific locations. Research in mice has shown that within the hippocampus, neurons called place cells fire when the animals are in a specific location, or even if they are dreaming about that location.

In the new study, the MIT team wanted to investigate whether the hippocampus also stores representations of more abstract elements of a memory. That is, instead of firing whenever you enter a particular restaurant, such cells might encode “dessert,” no matter where you’re eating it.

To test this hypothesis, the researchers measured activity in neurons of the CA1 region of the mouse hippocampus as the mice repeatedly ran a four-lap maze. At the end of every fourth lap, the mice were given a reward. As expected, the researchers found place cells that lit up when the mice reached certain points along the track. However, the researchers also found sets of cells that were active during one of the four laps, but not the others. About 30 percent of the neurons in CA1 appeared to be involved in creating this “event code.”

“This gave us the initial inkling that besides a code for space, cells in the hippocampus also care about this discrete chunk of experience called lap 1, or this discrete chunk of experience called lap 2, or lap 3, or lap 4,” Sun says.

To further explore this idea, the researchers trained mice to run a square maze on day 1 and then a circular maze on day 2, in which they also received a reward after every fourth lap. They found that the place cells changed their activity, reflecting the new environment. However, the same sets of lap-specific cells were activated during each of the four laps, regardless of the shape of the track. The lap-encoding cells’ activity also remained consistent when laps were randomly shortened or lengthened.

“Even in the new spatial locations, cells still maintain their coding for the lap number, suggesting that cells that were coding for a square lap 1 have now been transferred to code for a circular lap 1,” Sun says.

The researchers also showed that if they used optogenetics to inhibit sensory input from a part of the brain called the medial entorhinal cortex (MEC), lap-encoding did not occur. They are now investigating what kind of input the MEC region provides to help the hippocampus create memories consisting of chunks of an experience.

Two distinct codes

These findings suggest that, indeed, every time you eat dinner, similar memory cells are activated, no matter where or what you’re eating. The researchers theorize that the hippocampus contains “two mutually and independently manipulatable codes,” Sun says. One encodes continuous changes in location, time, and sensory input, while the other organizes an overall experience into smaller chunks that fit into known categories such as appetizer and dessert.

“We believe that both types of hippocampal codes are useful, and both are important,” Tonegawa says. “If we want to remember all the details of what happened in a specific experience, moment-to-moment changes that occurred, then the continuous monitoring is effective. But on the other hand, when we have a longer experience, if you put it into chunks, and remember the abstract order of the abstract chunks, that’s more effective than monitoring this long process of continuous changes.”

The new MIT results “significantly advance our knowledge about the function of the hippocampus,” says Gyorgy Buzsaki, a professor of neuroscience at New York University School of Medicine, who was not part of the research team.

“These findings are significant because they are telling us that the hippocampus does a lot more than just ‘representing’ space or integrating paths into a continuous long journey,” Buzsaki says. “From these remarkable results Tonegawa and colleagues conclude that they discovered an ‘event code,’ dedicated to organizing experience by events, and that this code is independent of spatial and time representations, that is, jobs also attributed to the hippocampus.”

Tonegawa and Sun believe that networks of cells that encode chunks of experiences may also be useful for a type of learning called transfer learning, which allows you to apply knowledge you already have to help you interpret new experiences or learn new things. Tonegawa’s lab is now working on trying to find cell populations that might encode these specific pieces of knowledge.

The research was funded by the RIKEN Center for Brain Science, the Howard Hughes Medical Institute, and the JPB Foundation.

Source: http://news.mit.edu/2020/neuroscience-memory-cells-interpret-new-0406