Posts tagged neuron
Articles and news from the latest research reports.
Young brain develops activity peaks while it is still growing
After a short period of growth, cultured networks of neurons regularly exhibit major activity in the absence of external stimulation. These “bursts” are entirely related to growth. At this stage, they have little to do with learning behaviour, as the network is still too young to sustain a process of memory formation. This has now for the first time been simulated for networks ranging in size from 10,000 to 50,000 neurons. The simulations provide insight into the role of the growth process in initial activity. Researchers at the University of Twente’s MIRA Institute recently published details of this work in PLOS ONE.
Functional maps within a single neuron
The presence and plasticity of dendritic ion channels are well established. However, the literature is divided on what specific roles these dendritic ion channels play in neuronal information processing, and there is no consensus on why neuronal dendrites should express diverse ion channels with different expression profiles. In this review, we present a case for viewing dendritic information processing through the lens of the sensory map literature, where functional gradients within neurons are considered as maps on the neuronal topograph. Under such a framework, drawing analogies from the sensory map literature, we postulate that the formation of intraneuronal functional maps is driven by the twin objectives of efficiently encoding inputs that impinge along different dendritic locations and of retaining homeostasis in the face of changes that are required in the coding process. In arriving at this postulate, we relate intraneuronal map physiology to the vast literature on sensory maps and argue that such a metaphorical association provides a fresh conceptual framework for analyzing and understanding single-neuron information encoding. We also describe instances where the metaphor presents specific directions for research on intraneuronal maps, derived from analogous pursuits in the sensory map literature. We suggest that this perspective offers a thesis for why neurons should express and alter ion channels in their dendrites and provides a framework under which active dendrites could be related to neural coding, learning theory, and homeostasis.
Research by scientists from the Centre for Brain Research at the University of Auckland has uncovered new information about the mechanisms underlying autism spectrum disorders (ASDs), to be published in the next issue of the prestigious Journal of Neuroscience.
Principal investigator, Dr Johanna Montgomery, says the findings are highly significant: “We’re moving beyond simply what happens in ASDs and starting to understand how it happens.”
The behavioural manifestations of ASDs are well documented and include impaired communication and socialisation, learning difficulties, and repetitive or stereotyped behaviours. These behavioural characteristics are in turn associated with a wide range of gene mutations. Many of these mutated genes are responsible for the production of specific proteins in the neurons of the brain.
Dr Montgomery and her team took a close look at parts of these neurons – the synapses, which are the structures that enable brain cells to communicate with each other. This cell to cell communication is vital for a healthy brain, and underlies how we learn, remember, move and sense.
In a complex cascade of chemical and electrical signalling, information is transmitted from one neuron to another at the synapses. This process is mediated by several families of protein, some of which form the bedrock of the synapse on the ‘listening’ side. Dr Montgomery’s team chose to investigate one of these proteins, known as Shank3, because it has been identified as vital to the communication process between two neurons, and because it is known to be mutated in ASDs.
How does the brain measure time?
(Image: bzztbomb)
Researchers at the University of Minnesota’s Center for Magnetic Resonance Research (CMRR) have found a small population of neurons that is involved in measuring time, which is a process that has traditionally been difficult to study in the lab.
In the study, which is published October 30 in the open access journal PLOS Biology, the researchers developed a task in which monkeys could only rely on their internal sense of the passage of time. Their task design eliminated all external cues which could have served as “clocks”.
The monkeys were trained to move their eyes consistently at regular time intervals without any external cues or immediate expectation of reward. Researchers found that despite the lack of sensory information, the monkeys were remarkably precise and consistent in their timed behaviors. This consistency could be explained by activity in a specific region of the brain called the lateral intraparietal area (LIP). Interestingly, the researchers found that LIP activity during their task was different from activity in previous studies that had failed to eliminate external cues or expectation of reward.
"In contrast to previous studies that observed a build-up of activity associated with the passage of time, we found that LIP activity decreased at a constant rate between timed movements," said lead researcher Geoffrey Ghose, Ph.D., associate professor of neuroscience at the University of Minnesota. "Importantly, the animals’ timing varied after these neurons were more, or less, active. It’s as if the activity of these neurons was serving as an internal hourglass."
By developing a model to help explain the differences in timing signals they see relative to previous studies, their study also suggests that there is no “central clock” in the brain that is relied upon for all tasks involving timing. Instead, it appears as though each of the brain’s circuits responsible for different actions are capable of independently producing an accurate timing signal.
One important direction for future research is to explore how such precise timing signals arise as a consequence of practice and learning, and whether, when the signals are altered, there are clear effects on behavior.
(Source: medicalxpress.com)
Empathy represses analytic thought, and vice versa
New research shows a simple reason why even the most intelligent, complex brains can be taken by a swindler’s story – one that upon a second look offers clues it was false.
When the brain fires up the network of neurons that allows us to empathize, it suppresses the network used for analysis, a pivotal study led by a Case Western Reserve University researcher shows.
How could a CEO be so blind to the public relations fiasco his cost-cutting decision has made?
When the analytic network is engaged, our ability to appreciate the human cost of our action is repressed.
At rest, our brains cycle between the social and analytical networks. But when presented with a task, healthy adults engage the appropriate neural pathway, the researchers found.
The study shows for the first time that we have a built-in neural constraint on our ability to be both empathetic and analytic at the same time
The work suggests that established theories about two competing networks within the brain must be revised. More, it provides insights into the operation of a healthy mind versus those of the mentally ill or developmentally disabled.
“This is the cognitive structure we’ve evolved,” said Anthony Jack, an assistant professor of cognitive science at Case Western Reserve and lead author of the new study. “Empathetic and analytic thinking are, at least to some extent, mutually exclusive in the brain.”
The research is published in the current online issue of NeuroImage.
Primates’ brains make visual maps using triangular grids
Primates’ brains see the world through triangular grids, according to a new study published online Sunday in the journal Nature.
Scientists at Yerkes National Primate Research Center, Emory University, have identified grid cells, neurons that fire in repeating triangular patterns as the eyes explore visual scenes, in the brains of rhesus monkeys.
The finding has implications for understanding how humans form and remember mental maps of the world, as well as how neurodegenerative diseases such as Alzheimer’s erode those abilities. This is the first time grid cells have been detected directly in primates. Grid cells were identified in rats in 2005, and their existence in humans has been indirectly inferred through magnetic resonance imaging.
Grid cells’ electrical activities were recorded by introducing electrodes into monkeys’ entorhinal cortex, a region of the brain in the medial temporal lobe. At the same time, the monkeys viewed a variety of images on a computer screen and explored those images with their eyes. Infrared eye-tracking allowed the scientists to follow which part of the image the monkey’s eyes were focusing on. A single grid cell fires when the eyes focus on multiple discrete locations forming a grid pattern.
"The entorhinal cortex is one of the first brain regions to degenerate in Alzheimer’s disease, so our results may help to explain why disorientation is one of the first behavioral signs of Alzheimer’s," says senior author Elizabeth Buffalo, PhD, associate professor of neurology at Emory University School of Medicine and Yerkes National Primate Research Center. "We think these neurons help provide a context or structure for visual experiences to be stored in memory."
"Our discovery of grid cells in primates is a big step toward understanding how our brains form memories of visual information," says first author Nathan Killian, a graduate student in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University. "This is an exciting way of thinking about memory that may lead to novel treatments for neurodegenerative diseases."
(Image credit: Mark Snelson)
Same neurons at work in sleep and under anesthesia
Anesthesiologists aren’t totally lying when they say they’re going to put you to sleep. Some anesthetics directly tap into sleep-promoting neurons in the brain, a study in mice reveals.
The results may help clarify how drugs that have been used around the world for decades actually put someone under. “It’s kind of shocking that after 170 years, we still don’t understand why they work,” says study coauthor Max Kelz of the University of Pennsylvania in Philadelphia.
Most neurons in the brain appear to be calmed by anesthetics, says neuropharmacologist and anesthesiologist Hugh Hemmings Jr. of Weill Cornell Medical College in New York City. But the new results, published online October 25 in Current Biology, show that two common anesthetics actually stimulate sleep-inducing neurons. “It’s unusual for neurons to be excited by anesthetics,” Hemmings says.
In the study, Kelz, Jason Moore, also of the University of Pennsylvania, and colleagues studied the effects of the anesthetics isoflurane and halothane. Mice given the drugs soon became sleepy, as expected. Along with this drowsiness came a jump in nerve cell activity in a part of the brain’s hypothalamus called the ventrolateral preoptic nucleus, or VLPO.
Sensory Neurons Identified as Critical to Sense of Touch
While studying the sense of touch, scientists at Duke Medicine have pinpointed specific neurons that appear to regulate perception. The sensory neurons are characterized by thin spikes, and based on their volume, these protrusions determine the cells’ sensitivity to force.
The findings in fruit fly larvae, which appear in online Oct. 25, 2012, in the journal Current Biology, demonstrate the first known function for the sensory neurons and provide insights that could broaden the understanding of chronic pain syndromes in humans.
"On a molecular level, touch is the most poorly understood of the senses," said W. Daniel Tracey, PhD, associate professor of anesthesiology at Duke University Medical Center and study author. "While there are many types of touch sensor neurons, we still don’t know how these neurons respond to force."
“Grassroots” Neurons Wire and Fire Together for Dominance in the Brain
Inside the brain, an unpredictable race—like a political campaign—is being run. Multiple candidates, each with a network of supporters, have organized themselves into various left- and right-wing clusters—like grassroots political teams working feverishly to reinforce a vision that bands them together. While scientists know that neurons in the brain anatomically organize themselves into these network camps, or clusters, the implications of such groupings on neural dynamics have remained unclear until now.
Using mathematical modeling, two researchers from the University of Pittsburgh have found that neurons team up together to sway particular outcomes in the brain and take over the nervous system in the name of their preferred action or behavior. The findings will be published in the November print issue of Nature Neuroscience.
“Through complex mathematical equations, we organized neurons into clustered networks and immediately saw that our model produced a rich dynamic wherein neurons in the same groups were active together,” said Brent Doiron, assistant professor of mathematics.
Neuroscientists propose a revolutionary DNA-based approach to map wiring of the whole brain
A team of neuroscientists have proposed a new and potentially revolutionary way of obtaining a neuronal connectivity map (the “connectome”) of the whole brain of the mouse. The details are set forth in an essay published October 23 in the open-access journal PLOS Biology.
The team, led by Professor Anthony Zador, Ph.D., of Cold Spring Harbor Laboratory, aims to provide a comprehensive account of neural connectivity. At present the only method for obtaining this information with high precision relies on examining individual cell-to-cell contacts (synapses) in electron microscopes. But such methods are slow, expensive and labor-intensive.
Zador and colleagues instead propose to exploit high-throughput DNA sequencing to probe the connectivity of neural circuits at the resolution of single neurons.
“Our method renders the connectivity problem in a format in which the data are readable by currently available high-throughput genome sequencing machines,” says Zador. “We propose to do this via a process we’re now developing, called BOINC: the barcoding of individual neuronal connections.”
The proposal comes at a time when a number of scientific teams in the U.S. are progressing in their efforts to map connections in the mammalian brain. These efforts use injections of tracer dyes or viruses to map neuronal connectivity at a “mesoscopic” scale—a mid-range resolution that makes it possible to follow neural fibers between brain regions. Other groups are scaling up approaches based on electron microscopy.