Posts tagged neuroimaging
Articles and news from the latest research reports.
Brain scans have revealed distinctive features in the brain structure of karate experts that are associated with how well they performed in a test of punching ability.
Researchers from Imperial College London and UCL looked for differences in brain structure between 12 karate practitioners with a black belt rank and an average of 13.8 years’ karate experience, and 12 people of similar age who exercised regularly but did not have any martial arts experience.
Dr Ed Roberts, from the Department of Medicine at Imperial College London, who led the study, explained: "The karate black belts were able to repeatedly coordinate their punching action with a level of coordination that novices can’t produce. We think that ability might be related to fine-tuning of neural connections in the cerebellum, allowing them to synchronise their arm and trunk movements very accurately."
The scans used in this study, called diffusion tensor imaging (DTI), detected structural differences in the white matter of parts of the brain called the cerebellum and the primary motor cortex, which are known to be involved in controlling movement. The differences measured by DTI in the cerebellum correlated with the synchronicity of the subjects’ wrist and shoulder movements when punching.
The DTI signal also correlated with the age at which karate experts began training and their total experience of the discipline. These findings suggest that the structural differences in the brain are related to the black belts’ punching ability.
(Image credit: Adam J. Merton on Flickr)
A group of researchers has developed some exciting new techniques for imaging neuronal and synaptic networks using the hard synchrotron x-rays provided by the U.S. Department of Energy Office of Science’s Advanced Photon Source (APS).
These techniques provide images with unprecedented detail and resolution, and open the door to three-dimensional tomographic reconstructions, a vital tool for studying the complex tree-like branching nature of neuronal networks.
Understanding intricate neuronal and synaptic networks, particularly in more complex mammalian brains, requires high-resolution mapping of large volumes of tissue, preferably in three dimensions in order to capture all the subtle structural details.
"Mapping neuron networks has been providing a very significant understanding of how the brain works," said Yeukwang Hwu of Academia Sinica in Taipei, Taiwan, lead author of the paper on this new study, which was published in the Journal of Physics D: Applied Physics.
Brain might not stand in the way of free will
Advocates of free will can rest easy, for now. A 30-year-old classic experiment that is often used to argue against free will might have been misinterpreted.
Our decision-making process remains hazy (Image: Jannes Glas/Getty)
In the early 1980s, Benjamin Libet, a neuroscientist at the University of California in San Francisco, used electroencephalography (EEG) to record the brain activity of volunteers who had been told to make a spontaneous movement. With the help of a precise timer that the volunteers were asked to read at the moment they became aware of the urge to act, Libet found there was a 200 millisecond delay, on average, between this urge and the movement itself.
But the EEG recordings also revealed a signal that appeared in the brain even earlier, 550 milliseconds, on average, before the action. Called the readiness potential, this has been interpreted as a blow to free will, as it suggests that the brain prepares to act well before we are conscious of the urge to move.
This conclusion assumes that the readiness potential is the signature of the brain planning and preparing to move. “Even people who have been critical of Libet’s work, by and large, haven’t challenged that assumption,” says Aaron Schurger of the National Institute of Health and Medical Research in Saclay, France.
One attempt to do so came in 2009. Judy Trevena and Jeff Miller of the University of Otago in Dunedin, New Zealand, asked volunteers to decide, after hearing a tone, whether or not to tap on a keyboard. The readiness potential was present regardless of their decision, suggesting that it did not represent the brain preparing to move. Exactly what it did mean, though, still wasn’t clear.
Crossing a threshold
Now, Schurger and colleagues have an explanation. They began by posing a question: how does the brain decide to make a spontaneous movement? They looked to other decision-making scenarios for clues. Previous studies have shown that when we have to make a decision based on visual input, for example, assemblies of neurons start accumulating visual evidence in favour of the various possible outcomes. A decision is triggered when the evidence favouring one particular outcome becomes strong enough to tip its associated assembly of neurons across a threshold.
Schurger’s team hypothesised that something similar happens in the brain during the Libet experiment. Volunteers, however, are specifically asked to ignore any external signals before they make a spontaneous movement, so the signal must be internal.
There are random fluctuations of neural activity in the brain. Schurger’s team reasoned that movement is triggered when this neural noise accumulates and crosses a threshold.
To probe the idea, the team first built a computer model of such a neural accumulator. In the model, each time the neural noise crossed a threshold it signified a decision to move. They found that when they ran the model numerous times and looked at the pattern of the neural noise that led up to the decision it looked like a readiness potential.
Next, the team repeated Libet’s experiment, but this time if, while waiting to act spontaneously, the volunteers heard a click they had to act immediately. The researchers predicted that the fastest response to the click would be seen in those in whom the accumulation of neural noise had neared the threshold – something that would show up in their EEG as a readiness potential.
This is exactly what the team found. In those with slower responses to the click, the readiness potential was absent in the EEG recordings.
Spontaneous brain activity
"Libet argued that our brain has already decided to move well before we have a conscious intention to move," says Schurger. "We argue that what looks like a pre-conscious decision process may not in fact reflect a decision at all. It only looks that way because of the nature of spontaneous brain activity."
So what does this say about free will? “If we are correct, then the Libet experiment does not count as evidence against the possibility of conscious will,” says Schurger.
Cognitive neuroscientist Anil Seth of the University of Sussex in Brighton, UK, is impressed by the work, but also circumspect about what it says about free will. “It’s a more satisfying mechanistic explanation of the readiness potential. But it doesn’t bounce conscious free will suddenly back into the picture,” he says. “Showing that one aspect of the Libet experiment can be open to interpretation does not mean that all arguments against conscious free will need to be ejected.”
According to Seth, when the volunteers in Libet’s experiment said they felt an urge to act, that urge is an experience, similar to an experience of smell or taste. The new model is “opening the door towards a richer understanding of the neural basis of the conscious experience of volition”, he says.
Source: NewScientist
Irony seen through the eye of MRI
A French team has shown that the activation of the ToM neural network increases when an individual is reacting to ironic statements. Published in Neuroimage, these findings represent an important breakthrough in the study of Theory of Mind and linguistics, shedding light on the mechanisms involved in interpersonal communication.
In our communications with others, we are constantly thinking beyond the basic meaning of words. For example, if asked, “Do you have the time?” one would not simply reply, “Yes.” The gap between what is said and what it means is the focus of a branch of linguistics called pragmatics. In this science, “Theory of Mind” (ToM) gives listeners the capacity to fill this gap. In order to decipher the meaning and intentions hidden behind what is said, even in the most casual conversation, ToM relies on a variety of verbal and non-verbal elements: the words used, their context, intonation, “body language,” etc.
Researchers at Aalto University in Finland have developed the world’s first device designed for mapping the human brain that combines whole-head magnetoencephalography (MEG) and magnetic resonance imaging (MRI) technology. MEG measures the electrical function and MRI visualizes the structure of the brain. The merging of these two technologies will produce unprecedented accuracy in locating brain electrical activity non-invasively.
Alzheimer’s plaques in PET brain scans identify future cognitive decline
July 11, 2012
Among patients with mild or no cognitive impairment, brain scans using a new radioactive dye can detect early evidence of Alzheimer’s disease that may predict future decline, according to a multi-center study led by researchers at Duke University Medical Center.
PET images using florbetapir dye to highlight beta-amyloid plaques show (A), a cognitively normal subject; (B) an amyloid-positive patient with Alzheimer’s disease; (C) a patient with mild cognitive impairment; and (D) a patient with mild cognitive impairment who progressed to dementia during the study. Credit: Slide courtesy of the journal Neurology.
The finding is published online July 11, 2012, in the journal Neurology, the medical journal of the American Academy of Neurology. It expands on smaller studies demonstrating that early detection of tell-tale plaques could be a predictive tool to help guide care and treatment decisions for patients with Alzheimer’s disease.
"Even at a short follow-up of 18 months we can see how the presence of amyloid plaques affects cognitive function," said P. Murali Doraiswamy, M.D., professor of psychiatry at Duke who co-led the study with R. Edward Coleman, M.D., professor of radiology at Duke . "Most people who come to the doctor with mild impairment really want to know the short-term prognosis and potential long-term effect."
Doraiswamy said such knowledge also has some pitfalls. There is no cure for Alzheimer’s disease, which afflicts 5.4 million people in the United States and is the sixth-leading cause of death among U.S. adults. But he said numerous drugs are being investigated, and identifying earlier disease would improve research into their potential benefits and speed new discoveries, while also enhancing care and treatment of current patients.
In the Neurology study, 151 people who had enrolled in a multi-center test of a new radioactive dye called florbetapir (Amyvid) were recruited to participate in a 36-month analysis. Of those participants, 69 had normal cognitive function at the start of the study, 51 had been diagnosed with mild impairment, and 31 had Alzheimer’s dementia.
All completed cognitive tests and underwent a brain scan using Positron Emission Tomography, or PET imaging. The technology uses radioactive tracers designed to highlight specific tissue to create a three-dimensional picture of an organ or a biological function.
The dye used in the study, florbetapir, was recently approved by the U.S. Food and Drug Administration for PET imaging of the brain to estimate beta-amyloid plaque density in patients who are being evaluated for cognitive impairment. It binds to the amyloid plaques that characterize Alzheimer’s disease, providing a window into the brain to see if the plaques have formed, and how extensively.
Patients in the study were reassessed with additional cognitive exams at 18 months and 36 months. At the 18-month point, patients with mild cognitive impairment who had PET evidence of plaque at the trial’s start worsened to a great degree on cognitive tests than patients who had no evidence of plaque at the trial’s start. Twenty-nine percent of the plaque-positive patients in this group developed Alzheimer’s dementia, compared to 10 percent who started with no plaque.
Cognitively normal patients with a plaque-positive PET scan at the start of the study also showed more mental decline at 18 months compared to those who were negative for plaque.
The study additionally found that people with negative scans reversed from minimally impaired to normal more often than people with positive PET scan, suggesting test anxiety or concentration problems could have affected their initial performance.
"For the most part we have been blind about who would progress and who wouldn’t, so this approach is a step toward having a biomarker that predicts risk of decline in people who are experiencing cognitive impairment," Doraiswamy said.
He said the study’s results provide initial data that needs to be verified by additional research. Final, 36-month data from the study has been completed and will be presented at the Alzheimer’s Association International Conference this week in Vancouver, Canada. Doraiswamy also cautioned that florbetapir is currently not approved to predict the development of dementia or other neurologic conditions and stressed that it should not be used as a screening tool in otherwise normal or minimally impaired people. Likewise, a positive scan is not necessarily diagnostic for Alzheimer’s by itself.
Provided by Duke University Medical Center
Source: medicalxpress.com
Baby’s birth captured in MRI movie for the first time
Mother gave birth in a specially-designed ‘open’ MRI scanner. The footage shows that each time the uterus contracts it exerts pressure on the baby sliding him further down the birth canal. When the contraction is over the uterus relaxes and the baby’s head recedes slightly.