Of all the many ways the teeming ecosystem of microbes in a person’s gut and other tissues might affect health, its potential influences on the brain may be the most provocative. Now, a study of two large groups of Europeans has found several species of gut bacteria are missing in people with depression. The researchers can’t say whether the absence is a cause or an effect of the illness, but they showed that many gut bacteria could make substances that affect nerve cell function—and maybe mood.
“It’s the first real stab at tracking how” a microbe’s chemicals might affect mood in humans, says John Cryan, a neuroscientist at University College Cork in Ireland who has been one of the most vocal proponents of a microbiome-brain connection. The study “really pushes the field from where it’s been” with small studies of depressed people or animal experiments. Interventions based on the gut microbiome are now under investigation: The University of Basel in Switzerland, for example, is planning a trial of fecal transplants, which can restore or alter the gut microbiome, in depressed people.
Several studies in mice had indicated that gut microbes can affect behavior, and small studies of people suggested this microbial repertoire is altered in depression. To test the link in a larger group, Jeroen Raes, a microbiologist at the Catholic University of Leuven in Belgium, and his colleagues took a closer look at 1054 Belgians they had recruited to assess a “normal” microbiome. Some in the group—173 in total—had been diagnosed with depression or had done poorly on a quality of life survey, and the team compared their microbiomes with those other participants. Two kinds of microbes, Coprococcus and Dialister, were missing from the microbiomes of the depressed subjects, but not from those with a high quality of life. The finding held up when the researchers allowed for factors such as age, sex, or antidepressant use, all of which influence the microbiome, the team reports today in Nature Microbiology. They also found the depressed people had an increase in bacteria implicated in Crohn disease, suggesting inflammation may be at fault. [Continue reading…]
Evidence mounts that gut bacteria can influence mood, prevent depression
The cerebellum is your ‘little brain’ — and it does some pretty big things
For the longest time the cerebellum, a dense, fist-size formation located at the base of the brain, never got much respect from neuroscientists.
For about two centuries the scientific community believed the cerebellum (Latin for “little brain”), which contains approximately half of the brain’s neurons, was dedicated solely to the control of movement. In recent decades, however, the tide has started to turn, as researchers have revealed details of the structure’s role in cognition, emotional processing and social behavior.
The longstanding interest in the cerebellum can be seen in the work of French physiologist Marie Jean Pierre Flourens—(1794–1867). Flourens removed the cerebella of pigeons and found the birds became unbalanced, although they could still move. Based on these observations, he concluded the cerebellum was responsible for coordinating movements. “[This] set the dogma that the cerebellum was involved in motor coordination,” says Kamran Khodakhah, a neuroscientist at Albert Einstein College of Medicine, adding: “For many years, we ignored the signs that suggested it was involved in other things.”
One of the strongest pieces of evidence for the cerebellum’s broader repertoire emerged around two decades ago, when Jeremy Schmahmann, a neurologist at Massachusetts General Hospital, described cerebellar cognitive affective syndrome after discovering behavioral changes such as impairments in abstract reasoning and regulating emotion in individuals whose cerebella had been damaged. Since then this line of study has expanded. There has been human neuroimaging work showing the cerebellum is involved in cognitive processing and emotional control—and investigations in animals have revealed, among other things, that the structure is important for the normal development of social and cognitive capacities. Researchers have also linked altered cerebellar function to addiction, autism and schizophrenia.
Although many of these findings suggested the cerebellum played an important part both in reward-related and social behavior, a clear neural mechanism to explain this link was lacking. New research, published this week in Science, demonstrates that a pathway directly tying the cerebellum to the ventral tegmental area (VTA)—one of the brain’s key pleasure centers—can control these two processes. [Continue reading…]
The brain maps out ideas and memories on spacial form of representation
We humans have always experienced an odd — and oddly deep — connection between the mental worlds and physical worlds we inhabit, especially when it comes to memory. We’re good at remembering landmarks and settings, and if we give our memories a location for context, hanging on to them becomes easier. To remember long speeches, ancient Greek and Roman orators imagined wandering through “memory palaces” full of reminders. Modern memory contest champions still use that technique to “place” long lists of numbers, names and other pieces of information.
As the philosopher Immanuel Kant put it, the concept of space serves as the organizing principle by which we perceive and interpret the world, even in abstract ways. “Our language is riddled with spatial metaphors for reasoning, and for memory in general,” said Kim Stachenfeld, a neuroscientist at the British artificial intelligence company DeepMind.
In the past few decades, research has shown that for at least two of our faculties, memory and navigation, those metaphors may have a physical basis in the brain. A small seahorse-shaped structure, the hippocampus, is essential to both those functions, and evidence has started to suggest that the same coding scheme — a grid-based form of representation — may underlie them. Recent insights have prompted some researchers to propose that this same coding scheme can help us navigate other kinds of information, including sights, sounds and abstract concepts. The most ambitious suggestions even venture that these grid codes could be the key to understanding how the brain processes all details of general knowledge, perception and memory. [Continue reading…]
How new data is transforming our understanding of the brain’s navigational place cells
The first pieces of the brain’s “inner GPS” started coming to light in 1970. In the laboratories of University College London, John O’Keefe and his student Jonathan Dostrovsky recorded the electrical activity of neurons in the hippocampus of freely moving rats. They found a group of neurons that increased their activity only when a rat found itself in a particular location. They called them “place cells.”
Building on these early findings, O’Keefe and his colleague Lynn Nadel proposed that the hippocampus contains an invariant representation of space that does not depend on mood or desire. They called this representation the “cognitive map.” In their view, all of the brain’s place cells together represent the entirety of an animal’s environment, and whichever place cell is active indicates its current location. In other words, the hippocampus is like a GPS. It tells you where you are on a map and that map remains the same whether you are hungry and looking for food or sleepy and looking for a bed. O’Keefe and Nadel suggested that the absolute position represented in the hippocampal place cells provides a mental framework that can be used by an animal to find its way in any situation—be that to find food or a bed.
Over the next 40 years, other researchers—including the husband and wife duo of Edvard and May-Britt Moser—produced support for the idea that the brain’s hippocampal circuitry acts like an inner GPS. In recognition of their pioneering work, O’Keefe and the Mosers were awarded the 2014 Nobel Prize in physiology or medicine. You’d think that this would mean that the role of the hippocampus in guiding an animal through space was solved.
But studying the brain is never that straightforward. Like a match lighting a fuse, the 2014 Nobel Prize set off an explosion of experiments and ideas, some of which have pushed back against O’Keefe and Nadel’s early interpretation. This new work has suggested that when it comes to spatial navigation, the hippocampal circuit represents location information that is relative and malleable by experience rather than absolute. The study of the hippocampus seems to have stumbled into an age-old philosophical argument. [Continue reading…]
The battle over whether new nerve cells can develop in adult brains intensifies
Just a generation ago, common wisdom held that once a person reaches adulthood, the brain stops producing new nerve cells. Scientists countered that depressing prospect 20 years ago with signs that a grown-up brain can in fact replenish itself. The implications were huge: Maybe that process would offer a way to fight disorders such as depression and Alzheimer’s disease.
This year, though, several pieces of contradictory evidence surfaced and a heated debate once again flared up. Today, we still don’t know whether the fully grown brain churns out new nerve cells.This year’s opening shot came March 7 in a controversial report in Nature. Contradicting several landmark findings that had convinced the scientific community that adults can make new nerve cells, researchers described an utter lack of dividing nerve cells, or neurons, in adult postmortem brain tissue (SN Online: 3/8/18). A return volley came a month later, when a different research group described loads of newborn neurons in postmortem brains, in an April 5 paper in Cell Stem Cell (SN: 5/12/18, p. 10). Scientific whiplash ensued when a third group found no new neurons in postmortem brains, describing the results in the July Cerebral Cortex. Still more neuroscientists jumped into the fray with commentaries and perspective articles.
This ping-ponging over the rejuvenating powers of the brain is the most recent iteration of a question that still hasn’t been answered. [Continue reading…]
An ant colony has memories that its individual members don’t have
By Deborah M Gordon
Like a brain, an ant colony operates without central control. Each is a set of interacting individuals, either neurons or ants, using simple chemical interactions that in the aggregate generate their behaviour. People use their brains to remember. Can ant colonies do that? This question leads to another question: what is memory? For people, memory is the capacity to recall something that happened in the past. We also ask computers to reproduce past actions – the blending of the idea of the computer as brain and brain as computer has lead us to take ‘memory’ to mean something like the information stored on a hard drive. We know that our memory relies on changes in how much a set of linked neurons stimulate each other; that it is reinforced somehow during sleep; and that recent and long-term memory involve different circuits of connected neurons. But there is much we still don’t know about how those neural events come together, whether there are stored representations that we use to talk about something that happened in the past, or how we can keep performing a previously learned task such as reading or riding a bicycle.
Any living being can exhibit the simplest form of memory, a change due to past events. Look at a tree that has lost a branch. It remembers by how it grows around the wound, leaving traces in the pattern of the bark and the shape of the tree. You might be able to describe the last time you had the flu, or you might not. Either way, in some sense your body ‘remembers’, because some of your cells now have different antibodies, molecular receptors, which fit that particular virus.
Past events can alter the behaviour of both individual ants and ant colonies. Individual carpenter ants offered a sugar treat remembered its location for a few minutes; they were likely to return to where the food had been. Another species, the Sahara Desert ant, meanders around the barren desert, searching for food. It appears that an ant of this species can remember how far it walked, or how many steps it took, since the last time it was at the nest.
Could consciousness all come down to the way things vibrate?
agsandrew/Shutterstock.com
By Tam Hunt, University of California, Santa Barbara
Why is my awareness here, while yours is over there? Why is the universe split in two for each of us, into a subject and an infinity of objects? How is each of us our own center of experience, receiving information about the rest of the world out there? Why are some things conscious and others apparently not? Is a rat conscious? A gnat? A bacterium?
These questions are all aspects of the ancient “mind-body problem,” which asks, essentially: What is the relationship between mind and matter? It’s resisted a generally satisfying conclusion for thousands of years.
The mind-body problem enjoyed a major rebranding over the last two decades. Now it’s generally known as the “hard problem” of consciousness, after philosopher David Chalmers coined this term in a now classic paper and further explored it in his 1996 book, “The Conscious Mind: In Search of a Fundamental Theory.”
Chalmers thought the mind-body problem should be called “hard” in comparison to what, with tongue in cheek, he called the “easy” problems of neuroscience: How do neurons and the brain work at the physical level? Of course they’re not actually easy at all. But his point was that they’re relatively easy compared to the truly difficult problem of explaining how consciousness relates to matter.
Over the last decade, my colleague, University of California, Santa Barbara psychology professor Jonathan Schooler and I have developed what we call a “resonance theory of consciousness.” We suggest that resonance – another word for synchronized vibrations – is at the heart of not only human consciousness but also animal consciousness and of physical reality more generally. It sounds like something the hippies might have dreamed up – it’s all vibrations, man! – but stick with me.
How the brain tracks time
Our brains have an extraordinary ability to monitor time. A driver can judge just how much time is left to run a yellow light; a dancer can keep a beat down to the millisecond. But exactly how the brain tracks time is still a mystery. Researchers have defined the brain areas involved in movement, memory, color vision and other functions, but not the ones that monitor time. Indeed, our neural timekeeper has proved so elusive that most scientists assume this mechanism is distributed throughout the brain, with different regions using different monitors to keep track of time according to their needs.
Over the last few years, a handful of researchers have compiled growing evidence that the same cells that monitor an individual’s location in space also mark the passage of time. This suggests that two brain regions — the hippocampus and the entorhinal cortex, both famous for their role in memory and navigation — can also act as a sort of timer.
In research published in November [2015], Howard Eichenbaum, a neuroscientist at Boston University, and collaborators showed that cells in rats that form the brain’s internal GPS system, known as grid cells, are more malleable than had been anticipated. Typically these cells act like a dead-reckoning system, with certain neurons firing when an animal is in a specific place. (The researchers who discovered this shared the Nobel Prize in 2014.) Eichenbaum found that when an animal is kept in place — such as when it runs on a treadmill — the cells keep track of both distance and time. The work suggests that the brain’s sense of space and time are intertwined. [Continue reading…]
Navigation through the world and through the mind may involve the same neural pathways
Have you ever been in a semi-familiar location but couldn’t quite place where you were, then suddenly the landmarks line up and you know where you are? This might happen when entering a familiar location from an unusual direction, for example. Also (a seemingly unrelated question), when you visualize abstract ideas, do you arrange them physically. For example, do you visualize time (like days, weeks, months, years), and if so is there a particular physical relationship by which you mentally organize the progress of time?
Scientists from the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) and the Kavli Institute for Systems Neuroscience in Trondheim, Norway have published a paper in which they propose these two mental phenomena are directly related. One of the scientists, Edvard I. Moser, won the 2014 Nobel Prize for some of this work.
For background, researchers discovered that there are a type of neuron called place cells in the hippocampus (specifically area CA1) that store the memory for specific locations. When you are in a familiar location, a unique pattern of place cells will light up. Further, there is a second type of cell called grid neurons, which are arranged in a hexagonal pattern in the nearby entorhinal cortex. These grid cells light up in sequence as you move through your physical space – the physical arrangement of the grid neurons map to the physical arrangement of your environment.
This is an elegant system – your brain basically has a movable grid map, the grid keeps track of your local navigation, while the place cells keep track of where the map is.
This is also not the only example of so-called “somatotopic mapping” in the brain, where the physical location of neurons maps to their function. The other obvious example is the primary visual cortex. There the arrangement of neurons maps to the image itself, like a bitmap built of pixels, with each pixel being a neuron.
This kind of physical mapping is easy to understand, but now here is where the new paper comes in and where things get interesting. The authors propose that we navigate our abstract thoughts using the same neurons as for navigating physical space. [Continue reading…]
A tiny change in brain organization without which humans never could have evolved
Suzana Herculano-Houzel spent most of 2003 perfecting a macabre recipe—a formula for brain soup. Sometimes she froze the jiggly tissue in liquid nitrogen, and then she liquefied it in a blender. Other times she soaked it in formaldehyde and then mashed it in detergent, yielding a smooth, pink slurry.
Herculano-Houzel had completed her Ph.D. in neuroscience several years earlier, and in 2002, she had begun working as an assistant professor at the Federal University of Rio de Janeiro in Brazil. She had no real funding, no laboratory of her own—just a few feet of counter space borrowed from a colleague.
“I was interested in questions that could be answered with very little money [and] very little technology,” she recalls. Even so, she had a bold idea. With some effort—and luck—she hoped to accomplish something with her kitchen-blender project that had bedeviled scientists for over a century: to count the number of cells in the brain—not just the human brain, but also the brains of marmosets, macaque monkeys, shrews, giraffes, elephants, and dozens of other mammals.
Her method might have seemed carelessly destructive at first. How could annihilating such a fragile and complex organ provide any useful insights? But 15 years on, the work of Herculano-Houzel and her team has overturned some long-held ideas about the evolution of the human mind. It is helping to reveal the fundamental design principles of brains and the biological basis of intelligence: why some large brains lead to enhanced intelligence while others provide no benefit at all. Her work has unveiled a subtle tweak in brain organization that happened more than 60 million years ago, not long after primates branched off from their rodent-like cousins. It might have been a tiny change—but without it, humans never could have evolved. [Continue reading…]