Tag Archives: cortex

Our ability to read and write is housed in a ‘recycled’ part of the brain

New research is homing in on the mechanisms our brains use to process written language. 

A detail of the cuneiform script carved in basalt at the Van museum.
Image credits Verity Cridland / Flickr.

Given my profession, I’m quite happy that people can read and write. From an evolutionary standpoint, however, it’s surprising that we do. There’s no need for it in the wild, so our brains didn’t need to develop specific areas to handle the task, like they did with sight or hearing.

A new study looked into which areas of the brain handle this task, finding that we use a “recycled” brain area for reading. These structures were repurposed from the visual system and were originally involved in pattern recognition.

A change of career

“This work has opened up a potential linkage between our understanding of the neural mechanisms of visual processing and […] human reading,” says James DiCarlo, the head of MIT’s Department of Brain and Cognitive Sciences and the senior author of the study.

The findings suggest that even nonhuman primates have the ability to distinguish words from gibberish, or to pick out specific letters in a word, through a part of the brain called the inferotemporal (IT) cortex.

Previous research has used functional magnetic resonance imaging (fMRI) to identify which brain pathways activate when we read a word. Christened the visual word form area (VWFA), it handles the first step involved in reading: recognizing words in strings of letters or in unknown script. This area is located in the IT cortex, and is also responsible for distinguishing individual objects from visual data. The team also cites a 2012 study from France that showed baboons can learn to identify words within bunches of random letters.

DiCarlo and Dehaene wanted to see if this ability to process text is a natural part of the primate brain. They recorded neural activity patterns from 4 macaques as they were shown around 300 words and 300 ‘nonwords’ each. Data from the macaques was recorded at over 500 sites across their IT cortexes using surgically-implanted electrodes. This data was then fed through an algorithm that tried to determine whether the activity was caused by a word or not.

“The efficiency of this methodology is that you don’t need to train animals to do anything,” Rajalingham says. “What you do is just record these patterns of neural activity as you flash an image in front of the animal.”

Naturally good with letters

This model was 76% accurate at telling whether the animal was looking at a word or not, which is similar to the results of the baboons in the 2012 study.

As a control, the team performed the same experiment with data from a different brain area that is also tied to the IT and visual cortex. The accuracy of the model was worse compared to the experimental one (57% vs. 76%). This last part shows that the VWFA is particularly suited to handle the processes involved in letter and word recognition.

All in all, the findings support the hypothesis that the IT cortex could have been repurposed to enable reading, and that reading and writing themselves are an expression of our innate object recognition abilities.

Of course, whether reading and writing arose naturally from the way our brains work, or whether our brains had to shift to accommodate them, is a very interesting question — one that, for now, remains unanswered. The insight gained in this study, however, could help to guide us towards an answer there as well.

“These findings inspired us to ask if nonhuman primates could provide a unique opportunity to investigate the neuronal mechanisms underlying orthographic processing,” says Dehaene.

The next step, according to the researchers, is to train animals to read and see how their patterns of neural activity change as they learn.

The paper “The inferior temporal cortex is a potential cortical precursor of orthographic processing in untrained monkeys” has been published in the journal Nature Communications.

Noradrenaline levels may dictate whether you’re a light sleeper or not

New research points to noradrenaline (or norepinephrine), a neurotransmitter that’s secreted during stressful or dangerous situations, is what mediates our brain’s ability to block sensory responses during sleep.

Image via Pixabay.

Although we don’t remember much after the fact, our brains remain very active during sleep. However, the information it receives from our senses is heavily filtered — we don’t consciously perceive it, and only certain stimuli are able to rouse us from our sleep. Noradrenaline seems to underpin the process, according to the findings of a series of studies led by researchers at Tel Aviv University (TAU).

Peaceful slumber

“In these studies, we used different, novel approaches to study the filtering of sensory information during sleep and the brain mechanisms that determine when we awaken in response to external events,” explains Prof. Yuval Nir, who led the research for the three studies.

The first study, published April 1st in the Journal of Neuroscience, used rat models to show that neurons in the auditory cortex have similar responses to stimuli whether the animals were asleep or awake. Neurons in the perirhinal cortex however, which are involved in complex conscious perception and memory associations, showed much weaker responses during sleep.

He says that while our brains don’t create a conscious perception of sounds during sleep, “basic analysis of sound remains” active. Furthermore, “initial and fast responses are preserved in sleep” but more complex ones — which require coordination between different areas of the cortex — are significantly disrupted.

These findings, explains TAU doctoral student Yaniv Sela, challenge the current assumption that the thalamus is responsible for blocking incoming signals to the cerebral cortex while we sleep.

The second study, published a week later in Science Advances, reports that the locus coeruleus mediates the brain’s ability to disengage from sensory information during sleep in rats. The locus coeruleus is a small region of the brainstem and the main producer of noradrenaline in the brain.

“The ability to disconnect from the environment, in a reversible way, is a central feature of sleep,” explains TAU doctoral student Hanna Hayat, lead author of the study. “Our findings clearly show that the locus coeruleus noradrenaline system plays a crucial role in this disconnection by keeping a very low level of activity during sleep.”

The team monitored activity in the locus coeruleus of sleeping rats and exposed them to different sounds to see which would be able to wake them up. Activity in this area of the brain could reliably predict whether the animals would awake in response to a sound, they write.

To check their findings, the team used optogenetics (the use of genetically-modified cells that can be turned on or off through exposure to light) to inactivate the locus in sleeping rats — which dramatically reduced their likelihood of waking up in response to sound. Alternatively, the team reports that increasing noradrenaline activity in the locus coeruleus made the animals wake up more frequently in response to sound.

“So we can say we identified a powerful ‘dial’ that controls the depth of sleep despite external stimuli,” Hayat explains.

Heightened arousal in this brain area, the team explains, could explain why light sleepers or individuals experiencing stressful times have trouble staying asleep.

The first paper “Sleep Differentially Affects Early and Late Neuronal Responses to Sounds in Auditory and Perirhinal Cortices” has been published in the Journal of Neuroscience.

The second paper “Locus coeruleus norepinephrine activity mediates sensory-evoked awakenings from sleep” has been published in the journal Science Advances.

Walnut.

Your left hemisphere can veto the right one into submission — but they generally play nice

The two halves of your brain synchronize on a first-come-first-served basis, new research reveals — but the left side has the upper hand.

Walnut.

Image via Pixabay.

Our brain’s two hemispheres specialize in different tasks. In broad lines, the right hemisphere performs tasks that involve creativity, the left one handles tasks that have to do with logic, and each controls the movements of one half of the body.

Sounds quite complicated, huh? Well, it is. What makes the process even more complicated is that the brain often needs to reach a single response to a stimulus — in other words, one hemisphere needs to assert authority over the other, at times, and handle a specific scenario. Exactly how this power struggle is mediated, however, has remained unknown up to now.

Peas in a pod

A team of researchers from the Ruhr-Universität Bochum has worked to patch up our understanding on this subject, The team, comprised of Dr. Qian Xiao and Professor Onur Güntürkün, reports that hemispheric dominance is settled by slight differences in temporal activity patterns in both hemispheres — in pigeons, at least.

In other words, the first to act takes control. However, the team also found that in the case of a conflict, the left hemisphere can veto its counterpart and assume control.

The brain’s hemispheres are linked via a heavy-duty bundle of nerve fibers, known as commissures. It was assumed that these commissures carried signals from one hemisphere to the other, which helped them sync up. For example, one hemisphere could send inhibitory signals to its counterpart in order to suppress some of its functions. One big issue with that hypothesis, however, is that the hemispheres also broadcast excitatory signals over the commissures.

“This is why it has remained a mystery where, exactly, functional brain asymmetries stem from,” says Güntürkün.

The team approached the issue using a new method. At the biopsychology lab in Bochum, they measured the brain activity of pigeons performing a color differentiation test. From the readings, the team extrapolated the activity of individual cells in the birds’ visuomotor forebrain. This brain network handles visual information and generates movement as a response. In birds, the left hemisphere is dominant for these tasks.

Visual Tectomotor Pathways.

Ascending and descending pathways of the visual tectomotor pathways in pigeons.
Image credits Qian Xiao, Onur Güntürkün, 2018, Cell Reports.

The duo occasionally blocked the activity of neurons that sent signals over the commissures to better understand how the two hemispheres sync. They also monitored the neurons that usually receive input from the other hemisphere. By putting these sets of observations together, they were able to model how this interaction affects the activity of the two halves of the brain.

They report that if both hemispheres want to assert control, the left hemisphere comes on top — for some reason, it’s able to delay the activity of neurons in the right hemisphere and over-ride it, so to speak. The researchers further showed that the two hemispheres are also theoretically capable of synchronizing their activity.

“The right hemisphere simply acts too late to control the response,” Güntürkün explains.

“These results show that hemispheric dominance is based on a sophisticated mechanism. It does not hinge on one general inhibitory or excitatory influence; rather it is caused by minute temporal delays in the activity of nerve cells in the other hemisphere.”

The paper “Asymmetrical Commissural Control of the Subdominant Hemisphere in Pigeons” has been published in the journal Cell Reports.

Digital reconstruction of a rosehip neuron in the human brain. Credit: Tamas Lab, University of Szeged.

Scientists find a new type of neuron that may be unique to humans

Digital reconstruction of a rosehip neuron in the human brain. Credit: Tamas Lab, University of Szeged.

Digital reconstruction of a ‘rosehip neuron’ in the human brain. Credit: Tamas Lab, University of Szeged.

What makes humans so smart? No one’s really sure what makes our brains so special compared to those of other animals, but there are some hints that something special might occur at the cellular level. An intriguing new study supports this idea. In the paper, scientists describe the discovery of a new type of brain cell, one that doesn’t hasn’t been observed in animal models and could very well be unique to humans.

Remarkably, the new neuron was identified by two different research groups working independently from each other, using totally different techniques.

Gábor Tamás, a neuroscientist at the University of Szeged in Szeged, Hungary, along with colleagues conducted detailed examinations of the shape and electrical properties of cells collected from the neocortex.

The neocortex — the most complex part of the brain — is thought to be responsible for human consciousness and many other functions that we think of as unique to our species. It’s much larger, compared to our body size, than in other animals.

Meanwhile, in the United States, at the Allen Institute for Brain Science, researchers uncovered a suite of genes that encode brain cells but couldn’t be found in the genomes of any rodent.

While visiting the Allen Institute to present his latest research on specialized human brain cell types, Tamás was surprised to learn that his American colleagues had hit on the same cell using a very different technique.

“We realized that we were converging on the same cell type from absolutely different points of view,” Tamás said.

The two groups instantly decided to collaborate.

When looking under the microscope, Tamás and colleagues observed some odd-looking, bushy-shaped neurons. Because the dense bundle looked like a rose after it has shed its petals, the scientists named the cells “rosehip neurons”. They knew they had come across a new type of brain cell because the profile of the proteins coating the neuron’s membranes had never been seen in humans before.

These rosehip neurons are what scientists call inhibitory neurons, which interrupt the activity of other neurons in the brain. Much like traffic lights, this class of neurons stand at crossroads, exciting or blocking neural signals. Judging from their density, rosehip neurons make up roughly 10% to 15% of all inhibitory neurons in the outermost layer of the cortex. 

Rosehip neurons form synapses with another type of neuron in a different part of the human cortex, known as pyramidal neurons, which they likely block when the opportunity is right.

Tamás says inhibitory neurons are like the brakes on a car and rosehip neurons, in particular, would be the breaks that only work in a particular stop on your drive.

“This particular cell type — or car type — can stop at places other cell types cannot stop,” Tamás said. “The car or cell types participating in the traffic of a rodent brain cannot stop in these places.”

At the Allen Institute, in collaboration with the J. Craig Venter Institute, researchers found that rosehip neurons activate a unique set of genes that haven’t been seen in any mouse brain cell types they’ve studied before.

“Alone, these techniques are all powerful, but they give you an incomplete picture of what the cell might be doing,” said Rebecca Hodge, Senior Scientist at the Allen Institute for Brain Science and an author on the study. “Together, they tell you complementary things about a cell that can potentially tell you how it functions in the brain.”

We don’t know yet for sure if the newly identified type of neurons is unique to humans but the fact that they don’t exist in rodents is yet another indication of why lab mice aren’t by far the perfect model of human disease.

“Our brains are not just enlarged mouse brains,” said Trygve Bakken, Senior Scientist at the Allen Institute for Brain Science and an author on the study. “People have commented on this for many years, but this study gets at the issue from several angles.”

“Many of our organs can be reasonably modeled in an animal model,” Tamás said. “But what sets us apart from the rest of the animal kingdom is the capacity and the output of our brain. That makes us human. So it turns out humanity is very difficult to model in an animal system.”

In the future, the researchers plan on looking for rosehip neurons in other parts of the brain. They would also like to explore their potential role in brain disorders.

The findings appeared in the journal Nature Neuroscience. 

Detailed new map of human brain reveals almost 100 new regions

The human brain is one of the most complex phenomena known to man and despite extensive research, scientists have yet to fully understand it. Although a complete grasp of the nature of the human brain is still far-off, a new study by researchers from the Washington University School of Medicine brings us closer to this goal in the form of a detailed new map of the outermost layer of the brain, revealing almost 100 new regions.

The detailed new map of the human brain's cerebral cortex. Credit: Matthew Glasser and Eric Young

The detailed new map of the human brain’s cerebral cortex. Credit: Matthew Glasser and Eric Young

The outermost layer of the brain, referred to as the cerebral cortex, is a layer of neural tissue that encases that rest of the brain. It is the primary structure involved in sensory perception, attention, and numerous functions that are uniquely human, including language and abstract thinking.

In the new study, the team divided the cortex of the left and right cerebral hemispheres into 180 areas based on physical differences such as cortical thickness, functional differences and neural connectivity.

“The brain is not like a computer that can support any operating system and run any software,” said David Van Essen of the Washington University School of Medicine and senior author of the paper. “Instead, the software – how the brain works – is intimately correlated with the brain’s structure—its hardware, so to speak. If you want to find out what the brain can do, you have to understand how it is organized and wired.”

Matthew Glasser, lead author of the study, spearheaded the research after he realized that the current map of the human cortex – created by German neuroanatomist Korbinian Brodmann in the first decade of the 20th century – just wasn’t cutting it for modern research.

“My early work on language connectivity involved taking that 100-year-old map and trying to guess where Brodmann’s areas were in relation to the pathways underneath them,” Glasser said. “It quickly became obvious to me that we needed a better way to map the areas in the living brains that we were studying.”

Using data from 210 healthy young adults, both male and female, the team took measures of cortical thickness and neuronal cable insulation and combined them with magnetic resonance imaging (MRI) scans of the brain at rest as well as during simple tasks.

“We ended up with 180 areas in each hemisphere, but we don’t expect that to be the final number,” Glasser said. “In some cases, we identified a patch of cortex that probably could be subdivided, but we couldn’t confidently draw borders with our current data and techniques. In the future, researchers with better methods will subdivide that area. We focused on borders we are confident will stand the test of time.”

In the future, such cortical maps could be created on an individual basis and help in the diagnosis and treatment of neurological or psychiatric illnesses such as dementia and schizophrenia.

Journal Reference: A multi-modal parcellation of human cerebral cortex. 20 July 2016. 10.1038/nature18933

The making of a bully – childhood trauma is key

They say that the bully is actually the victim – and studies on adolescent rats seem to support this idea; younger rats subjected to a stressful environment turn out to be aggressive adults, behaviors that may be explained by accompanying epigenetic changes and altered brain activity. Whoa, let’s slow down a little.

ratMuch like humans, rats are also vulnerable to childhood trauma, becoming aggressive and pathologically violent later in life, according to a study published earlier this month in Translational Psychiatry. The team from Brain Mind Institute in Lausanne, Switzerland, observed that adult rats that had undergone traumatic experiences as adolescents exhibited violent behaviour in their adulthood – achange which was accompanied by epigenetic changes in the pre-frontal cortex. The pre-frontal cortex is the area of the brain responsible for planning complex cognitive behavior, personality expression, decision making and moderating social behavior.

“This work represents a critical advancement in our understanding of how our environment influences our behaviors and shapes our brains,” Fiona Hollis, a neuroscientist at the Brain Mind Institute, who did not participate in the study, wrote in an e-mail. “By demonstrating a link between early-life trauma and adult pathological aggression, we can better understand, and perhaps even reverse, the mechanisms underlying the cycle of violence, that is too often observed in society.”

Rats stressed in adolescence also presented anxiety and depression like features. They also displayed unusual hormone levels (particularly of high testosterone and low corticosterone levels – hormones associated with violence in humans). The changes went as far as to alter their DNA; however, when researchers injected them with a serotonin based inhibitor, their aggresivity level dwindled.

“The study consolidates the hypothesis that, altered serotonin signaling in limbic neural circuits, may form the core mechanism of stressed-induced pathological aggression,” Alexandre Dayer, a neuroscientist specializing in psychiatry and developmental neuroplasticity at the Geneva University Medical School, who was not involved in the study, said in an e-mail.

Source

Young people and Old people store information differently

The latest study conducted by researchers from the Duke University Medical Center was performed on two groups of (old and young) adults. The first group had an average age of about 70 while the younger ones were about 24 years old. Neuroscientists found out that the mechanism behind the part of the brain responsable for remembering (especially emotional content) was different for the two groups.

They were shown a group of 30 photographs; during the period in which they were shown the pictures, their brains were connected to a functional MRI (fMRI). The pictures varied in content and emotional impact; some had just neutral landscapes or pictures from nature, while some were very violent or just repulsive (such as snakes attacking, corpses, mutilated bodies, etc). They were then asked to place the pictures in a “pleasantness” scale. Then, the neuroscientists analyzed the data by interpreting how many neutral and negative pictures the groups missed.

The direct result was that the older people have less connectivity between the area that generates emotions and feelings and the part of the brain responsable for learning new things. Younger people used the part of the brain responsable for creating emotions to help them remember, while older people have a tighter connection with the frontal cortex.

“The younger adults were able to recall more of the negative photos,” said Roberto Cabeza, Ph.D., senior author and Duke professor in the Center for Cognitive Neuroscience. If the older adults are using more thinking than feeling, “that may be one reason why older adults showed a reduction in memory for pictures with a more negative emotional content.”

“It wasn’t surprising that older people showed a reduction in memory for negative pictures, but it was surprising that the older subjects were using a different system to help them to better encode those pictures they could remember,” said lead author Peggy St. Jacques, a graduate student in the Cabeza laboratory.

“Perhaps at different stages of life, there are different brain strategies,” Cabeza speculated. “Younger adults might need to keep an accurate memory for both positive and negative information in the world. Older people dwell in a world with a lot of negatives, so perhaps they have learned to reduce the impact of negative information and remember in a different way.” According to Cabeza, the results of the study are consistent with a theory about emotional processes in older adults proposed by Dr. Laura Carstensen at Stanford University, an expert in cognitive processing in old age.