Archive for the ‘Neuron’ Category

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What people experience as death creeps in—after the heart stops and the brain becomes starved of oxygen—seems to lie beyond the reach of science. But the authors of a new study on dying rats make a bold claim: After cardiac arrest, the rodents’ brains enter a state similar to heightened consciousness in humans. The researchers suggest that if the same is true for people, such brain activity could be the source of the visions and other sensations that make up so-called near-death experiences.

Estimated to occur in about 20% of patients who survive cardiac arrest, near-death experiences are frequently described as hypervivid or “realer-than-real,” and often include leaving the body and observing oneself from outside, or seeing a bright light. The similarities between these reports are hard to ignore, but the conversation about near-death experiences often bleeds into metaphysics: Are these visions produced solely by the brain, or are they a glimpse at an afterlife outside the body?

Neurologist Jimo Borjigin of the University of Michigan, Ann Arbor, got interested in near-death experiences during a different project—measuring the hormone levels in the brains of rodents after a stroke. Some of the animals in her lab died unexpectedly, and her measurements captured a surge in neurochemicals at the moment of their death. Previous research in rodents and humans has shown that electrical activity surges in the brain right after the heart stops, then goes flat after a few seconds. Without any evidence that this final blip contains meaningful brain activity, Borjigin says “it’s perhaps natural for people to assume that [near-death] experiences came from elsewhere, from more supernatural sources.” But after seeing those neurochemical surges in her animals, she wondered about those last few seconds, hypothesizing that even experiences seeming to stretch for days in a person’s memory could originate from a brief “knee-jerk reaction” of the dying brain.

To observe brains on the brink of death, Borjigin and her colleagues implanted electrodes into the brains of nine rats to measure electrical activity at six different locations. The team anesthetized the rats for about an hour, for ethical reasons, and then injected potassium chloride into each unconscious animal’s heart to cause cardiac arrest. In the approximately 30 seconds between a rat’s last heartbeat and the point when its brain stopped producing signals, the team carefully recorded its neuronal oscillations, or the frequency with which brain cells were firing their electrical signals.

The data produced by electroencephalograms (EEGs) of the nine rats revealed a highly organized brain response in the seconds after cardiac arrest, Borjigin and colleagues report online today in the Proceedings of the National Academy of Sciences. While overall electrical activity in the brain sharply declined after the last heartbeat, oscillations in the low gamma frequency (between 25 and 55 Hz) increased in power. Previous human research has linked gamma waves to waking consciousness, meditative states, and REM sleep. These oscillations in the dying rats were synchronized across different parts of the brain, even more so than in the rat’s normal waking state. The team also noticed that firing patterns in the front of the brain would be echoed in the back and sides. This so-called top-down signaling, which is associated with conscious perception and information processing, increased eightfold compared with the waking state, the team reports. When you put these features together, Borjigin says, they suggest that the dying brain is hyperactive in its final seconds, producing meaningful, conscious activity.

The team proposed that such research offers a “scientific framework” for approaching the highly lucid experiences that some people report after their brushes with death. But relating signs of consciousness in rat brains to human near-death experiences is controversial. “It opens more questions than it answers,” says Christof Koch, a neuroscientist at the Allen Institute for Brain Science in Seattle, Washington, of the research. Evidence of a highly organized and connected brain state during the animal’s death throes is surprising and fascinating, he says. But Koch, who worked with Francis Crick in the early 1980s to hypothesize that gamma waves are a hallmark of consciousness, says the increase in their frequency doesn’t necessarily mean that the rats were in a hyperconscious state. Not only is it impossible to project any mental experience onto these animals, but their response was also “still overlaid by the anesthesiology,” he says; this sedation likely influenced their brain response in unpredictable ways.

Others share Koch’s concerns. “There is no animal model of a near-death experience,” says critical care physician Sam Parnia of Stony Brook University School of Medicine in New York. We can never confirm what animals think or feel in their final moments, making it all but impossible to use them to study our own near-death experiences, he believes. Nonetheless, Parnia sees value in this new study from a clinical perspective, as a step toward understanding how the brain behaves right before death. He says that doctors might use a similar approach to learn how to improve blood flow or prolong electrical activity in the brain, preventing damage while resuscitating a patient.

Borjigin argues that the rat data are compelling enough to drive further study of near-death experiences in humans. She suggests monitoring EEG activity in people undergoing brain surgery that involves cooling the brain and reducing its blood supply. This procedure has prompted near-death experiences in the past, she says, and could offer a systematic way to explore the phenomenon.

read more here: http://news.sciencemag.org/brain-behavior/2013/08/probing-brain%E2%80%99s-final-moments

Thanks to Kebmodee for bringing this to the attention of the It’s Interesting community.

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by Leonie Welberg

The question of whether adult neurogenesis occurs in the human hippocampus has been a hotly debated topic in neuroscience. In a study published in Cell, Frisén and colleagues now settle the debate by providing evidence that around 1,400 dentate gyrus cells are born in the human brain every day.

The authors made use of a birth-dating method that is based on the principle that 14C in the atmosphere is taken up by plants and — because humans eat plants and animals that eat plants — eventually also by humans. As 14C is incorporated into DNA during cell division, the 14C content of a cell is thought to reflect 14C levels in the atmosphere at the time of the birth of the cell. Importantly, atomic bomb testing in the 1950s and 1960s resulted in a spike in atmospheric 14C levels, and levels declined after 1963; this means that the level of 14C in cellular DNA can be used as a relatively precise marker of a cell’s birth date.

The authors applied the 14C birth-dating method to whole hippocampi dissected from post-mortem brains donated by individuals who were born in different years in the twentieth century. They separated neurons from non-neuronal hippocampal cells, purified the neuronal DNA and determined 14C levels. Neuronal 14C levels did not match atmospheric 14C levels in the individual’s birth year but were either higher (for people born before 1950) or lower (for people born after 1963), suggesting that at least some of the hippocampal cells were born after the year in which an individual was born.

Computer modelling of the data revealed that the best-fit model was one in which 35% of hippocampal cells showed such turnover, whereas the majority did not (that is, they were born during development). Assuming that, in humans, adult neurogenesis would take place in the dentate gyrus rather than in other hippocampal areas (as it does in rodents), and as the dentate gyrus contains about 44% of all hippocampal neurons, this model suggests that about 80% of human dentate gyrus cells undergo renewal in adulthood. This is in striking contrast to the scenario in mice, in which only ~10% of adult dentate gyrus neurons undergo renewal. The study further showed that there is very little decline in the level of hippocampal neurogenesis with ageing in humans, which is again in contrast to rodents.

It is now well established that adult-born neurons have a functional role in the mouse and rat dentate gyrus and olfactory bulb. A previous study using the same neuronal birth-dating method established that no adult neurogenesis takes place in the olfactory bulb and cortex in humans, but the new study has elegantly shown that the situation is different in the dentate gyrus. Whether the adult-born neurons have functional implications in humans remains a topic for future investigation.

http://www.nature.com/nrn/journal/v14/n8/full/nrn3548.html?WT.ec_id=NRN-201308

Thanks to Kebmodee for bringing this to the attention of the It’s Interesting community.

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The flip of a single molecular switch helps create the mature neuronal connections that allow the brain to bridge the gap between adolescent impressionability and adult stability. Now Yale School of Medicine researchers have reversed the process, recreating a youthful brain that facilitated both learning and healing in the adult mouse.

Scientists have long known that the young and old brains are very different. Adolescent brains are more malleable or plastic, which allows them to learn languages more quickly than adults and speeds recovery from brain injuries. The comparative rigidity of the adult brain results in part from the function of a single gene that slows the rapid change in synaptic connections between neurons.

By monitoring the synapses in living mice over weeks and months, Yale researchers have identified the key genetic switch for brain maturation a study released March 6 in the journal Neuron. The Nogo Receptor 1 gene is required to suppress high levels of plasticity in the adolescent brain and create the relatively quiescent levels of plasticity in adulthood. In mice without this gene, juvenile levels of brain plasticity persist throughout adulthood. When researchers blocked the function of this gene in old mice, they reset the old brain to adolescent levels of plasticity.

“These are the molecules the brain needs for the transition from adolescence to adulthood,” said Dr. Stephen Strittmatter. Vincent Coates Professor of Neurology, Professor of Neurobiology and senior author of the paper. “It suggests we can turn back the clock in the adult brain and recover from trauma the way kids recover.”

Rehabilitation after brain injuries like strokes requires that patients re-learn tasks such as moving a hand. Researchers found that adult mice lacking Nogo Receptor recovered from injury as quickly as adolescent mice and mastered new, complex motor tasks more quickly than adults with the receptor.

“This raises the potential that manipulating Nogo Receptor in humans might accelerate and magnify rehabilitation after brain injuries like strokes,” said Feras Akbik, Yale doctoral student who is first author of the study.

Researchers also showed that Nogo Receptor slows loss of memories. Mice without Nogo receptor lost stressful memories more quickly, suggesting that manipulating the receptor could help treat post-traumatic stress disorder.

“We know a lot about the early development of the brain,” Strittmatter said, “But we know amazingly little about what happens in the brain during late adolescence.”

Other Yale authors are: Sarah M. Bhagat, Pujan R. Patel and William B.J. Cafferty

The study was funded by the National Institutes of Health. Strittmatter is scientific founder of Axerion Therapeutics, which is investigating applications of Nogo research to repair spinal cord damage.

http://news.yale.edu/2013/03/06/flip-single-molecular-switch-makes-old-brain-young

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After conducting the largest online intelligence study on record, a Western University-led research team has concluded that the notion of measuring one’s intelligence quotient or IQ by a singular, standardized test is highly misleading.

The findings from the landmark study, which included more than 100,000 participants, were published Dec. 19 in the journal Neuron. The article, “Fractionating human intelligence,” was written by Adrian M. Owen and Adam Hampshire from Western’s Brain and Mind Institute (London, Canada) and Roger Highfield, Director of External Affairs, Science Museum Group (London, U.K).

Utilizing an online study open to anyone, anywhere in the world, the researchers asked respondents to complete 12 cognitive tests tapping memory, reasoning, attention and planning abilities, as well as a survey about their background and lifestyle habits.

“The uptake was astonishing,” says Owen, the Canada Excellence Research Chair in Cognitive Neuroscience and Imaging and senior investigator on the project. “We expected a few hundred responses, but thousands and thousands of people took part, including people of all ages, cultures and creeds from every corner of the world.”

The results showed that when a wide range of cognitive abilities are explored, the observed variations in performance can only be explained with at least three distinct components: short-term memory, reasoning and a verbal component.

No one component, or IQ, explained everything. Furthermore, the scientists used a brain scanning technique known as functional magnetic resonance imaging (fMRI), to show that these differences in cognitive ability map onto distinct circuits in the brain.

With so many respondents, the results also provided a wealth of new information about how factors such as age, gender and the tendency to play computer games influence our brain function.

“Regular brain training didn’t help people’s cognitive performance at all yet aging had a profound negative effect on both memory and reasoning abilities,” says Owen.

Hampshire adds, “Intriguingly, people who regularly played computer games did perform significantly better in terms of both reasoning and short-term memory. And smokers performed poorly on the short-term memory and the verbal factors, while people who frequently suffer from anxiety performed badly on the short-term memory factor in particular.”

1.Adam Hampshire, Roger R. Highfield, Beth L. Parkin, Adrian M. Owen. Fractionating Human Intelligence. Neuron, 2012; 76 (6): 1225 DOI: 10.1016/j.neuron.2012.06.022

http://www.sciencedaily.com/releases/2012/12/121219133334.htm

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Our eyes may be our window to the world, but how do we make sense of the thousands of images that flood our retinas each day? Scientists at the University of California, Berkeley, have found that the brain is wired to put in order all the categories of objects and actions that we see. They have created the first interactive map of how the brain organizes these groupings.

The result — achieved through computational models of brain imaging data collected while the subjects watched hours of movie clips — is what researchers call “a continuous semantic space.”

“Our methods open a door that will quickly lead to a more complete and detailed understanding of how the brain is organized. Already, our online brain viewer appears to provide the most detailed look ever at the visual function and organization of a single human brain,” said Alexander Huth, a doctoral student in neuroscience at UC Berkeley and lead author of the study published Dec. 19 in the journal Neuron.

A clearer understanding of how the brain organizes visual input can help with the medical diagnosis and treatment of brain disorders. These findings may also be used to create brain-machine interfaces, particularly for facial and other image recognition systems. Among other things, they could improve a grocery store self-checkout system’s ability to recognize different kinds of merchandise.

“Our discovery suggests that brain scans could soon be used to label an image that someone is seeing, and may also help teach computers how to better recognize images,” said Huth.

It has long been thought that each category of object or action humans see — people, animals, vehicles, household appliances and movements — is represented in a separate region of the visual cortex. In this latest study, UC Berkeley researchers found that these categories are actually represented in highly organized, overlapping maps that cover as much as 20 percent of the brain, including the somatosensory and frontal cortices.

To conduct the experiment, the brain activity of five researchers was recorded via functional Magnetic Resonance Imaging (fMRI) as they each watched two hours of movie clips. The brain scans simultaneously measured blood flow in thousands of locations across the brain.

Researchers then used regularized linear regression analysis, which finds correlations in data, to build a model showing how each of the roughly 30,000 locations in the cortex responded to each of the 1,700 categories of objects and actions seen in the movie clips. Next, they used principal components analysis, a statistical method that can summarize large data sets, to find the “semantic space” that was common to all the study subjects.

The results are presented in multicolored, multidimensional maps showing the more than 1,700 visual categories and their relationships to one another. Categories that activate the same brain areas have similar colors. For example, humans are green, animals are yellow, vehicles are pink and violet and buildings are blue.

“Using the semantic space as a visualization tool, we immediately saw that categories are represented in these incredibly intricate maps that cover much more of the brain than we expected,” Huth said.

Other co-authors of the study are UC Berkeley neuroscientists Shinji Nishimoto, An T. Vu and Jack Gallant.

Journal Reference:

1.Alexander G. Huth, Shinji Nishimoto, An T. Vu, Jack L. Gallant. A Continuous Semantic Space Describes the Representation of Thousands of Object and Action Categories across the Human Brain. Neuron, 2012; 76 (6): 1210 DOI: 10.1016/j.neuron.2012.10.014

http://www.sciencedaily.com/releases/2012/12/121219142257.htm