Posts tagged neuroimaging
Articles and news from the latest research reports.
In Dyslexia, Less Brain Tissue Not to Blame for Reading Difficulties
In people with dyslexia, less gray matter in the brain has been linked to reading disabilities, but now new evidence suggests this is a consequence of poorer reading experiences and not the root cause of the disorder.
It has been assumed that the difference in the amount of gray matter might, in part, explain why dyslexic children have difficulties correctly and fluently mapping the sounds in words to their written counterparts during reading. But this assumption of causality has now been turned on its head.
The findings from anatomical brain studies conducted at Georgetown University Medical Center (GUMC) in the Center for the Study of Learning led by neuroscientist Guinevere Eden, DPhil, were published online today in The Journal of Neuroscience.
The study compared a group of dyslexic children with two different control groups: an age-matched group included in most previous studies, and a group of younger children who were matched at the same reading level as the children with dyslexia.
“This kind of approach allows us to control for both age as well as reading experience,” explains Eden, a professor of pediatrics at GUMC. “If the differences in brain anatomy in dyslexia were seen in comparison with both control groups, it would have suggested that reduced gray matter reflects an underlying cause of the reading deficit. But that’s not what we observed.”
The dyslexic groups showed less gray matter compared with a control group matched by age, consistent with previous findings. However, the result was not replicated when a control group matched by reading level was used as the comparison group with the dyslexics.
“This suggests that the anatomical differences reported in left hemisphere language processing regions appear to be a consequence of reading experience as opposed to a cause of dyslexia,” says Anthony Krafnick, PhD, lead author of the publication. “These results have an impact on how we interpret the previous anatomical literature on dyslexia and it suggests the use of anatomical MRI would not be a suitable way to identify children with dyslexia,” he says.
The work also helps to determine the fine line between experience-induced changes in the brain and differences that are the cause of cognitive impairment. For example, it is known from studies in illiterate people who attain reading skills as adults that this type of learning induces growth of brain matter. Similar learning-induced changes in typical readers may result in discrepancies between them and their dyslexic peers, who have not enjoyed the same reading experiences and thus have not undergone similar changes in brain structure.
Recall of stressful events caught in pictures
The study is of patients with conversion disorder (what Freud would have called Hysteria), which is still a very common disorder though rarely discussed or researched today.
“Freud started his whole theory by arguing that patients with hysteria repressed their memories of traumatic events and that this led to their developing their symptoms (of paralysis, for example) - what he called ‘conversion,” said Professor Richard Kanaan from the Department of Psychiatry, University of Melbourne and Austin Health.
“The world has pretty much given up on that theory largely because they thought it couldn’t be tested,” he said.
Published recently in the Journal of the American Medical Association, Psychiatry, the fMRI findings support Freud’s theories for the first time in over a century.
Researchers first painstakingly identified what they thought were the traumatic events that led to them becoming sick using the Life Events and Difficulties Schedule (LEDS) as a guide. This is a well-known psychological measurement for assessing life stress levels and experience.
“We got our patients to remember the traumatic events while we scanned their brains. Results showed something that looked like it could be them repressing their memories and possibly what could be them developing symptoms in response.”
“While it is still a preliminary study, in the history of psychiatry as a science it is potentially a significant breakthrough,” he said.
Researchers uncover secrets of newborn neurons
A new form of cell sub-division that is key to the development of the nervous system has been identified by researchers at the University of Dundee.
Image caption: Image shows two newborn neurons shedding their tip ends, or abscising
Neurons are vital to the development of the nervous system and in some regions of our brains they are continually produced throughout our lives. They are ‘born’ in a particular place in the early nervous system and then have to migrate to the correct place to make functional neural structures.
A team led by Professor Kate Storey and Dr Raman Das in the College of Life Sciences at Dundee have now identified a new process, apical abscission, which mediates the detachment of new-born neurons from the neural tube ventricle - freeing these cells to migrate.
'Neuron production is an important process within our bodies. As an example, our memory centre, the hippocampus, continues to produce neurons throughout our lives,' said Professor Storey.
'What we have identified are the molecular events, the 'letting-go' process, which allow newborn neurons to move to their correct place in the nervous system.
'This is a new form of cell sub-division so it is of significant interest as it tells us about mechanisms that control how we develop that we didn't know before. We were very surprised when we first saw cells shedding their tip-ends as they began to differentiate into neurons, it is not what we had expected at all.
'Our discovery comes with the development of novel live-tissue imaging approaches in my lab, which allows us to monitor cell behaviour over long periods. We have also been to make use of state of the art super-resolution microscopy in the Light Microscopy Facility based here within the College of Life Sciences.'
The research has been funded by the Wellcome Trust and the results are published this week in the journal Science.
The work identifies molecular events that control the shedding of the cell’s tip. It takes place as cells lose a key adhesion molecule and involves increased activity of a cell constriction mechanism.
Surprisingly, this event, also involves dismantling of an important structure in the cell, the primary cilium, known to convey signals that promote cell proliferation. Das and Storey propose that Apical Abscission mediates a pivotal cell state transition in the neuronal differentiation process, rapidly altering the polarity and signalling activity of the new-born neuron.
The researchers plan to extend the work to determine if this new mechanism also operates in other contexts including different regions of the brain, but will also address if this takes place in some cancers, where cells are known to lose polarity, shed primary cilia and detach from their neighbours as a prelude to tissue invasion.
'We need to look more widely now to establish whether this regulated mechanism allows other cells to make rapid cell state transitions and to move in other tissues of the body,' said Professor Storey.
(Source: dundee.ac.uk)
A novel look at how stories may change the brain
Many people can recall reading at least one cherished story that they say changed their life. Now researchers at Emory University have detected what may be biological traces related to this feeling: Actual changes in the brain that linger, at least for a few days, after reading a novel.
Their findings, that reading a novel may cause changes in resting-state connectivity of the brain that persist, were published by the journal Brain Connectivity.
“Stories shape our lives and in some cases help define a person,” says neuroscientist Gregory Berns, lead author of the study and the director of Emory’s Center for Neuropolicy. “We want to understand how stories get into your brain, and what they do to it.”
His co-authors included Kristina Blaine and Brandon Pye from the Center for Neuropolicy, and Michael Prietula, professor of information systems and operations management at Emory’s Goizueta Business School.
Neurobiological research using functional magnetic resonance imaging (fMRI) has begun to identify brain networks associated with reading stories. Most previous studies have focused on the cognitive processes involved in short stories, while subjects are actually reading them as they are in the fMRI scanner.
The Emory study focused on the lingering neural effects of reading a narrative. Twenty-one Emory undergraduates participated in the experiment, which was conducted over 19 consecutive days.
All of the study subjects read the same novel, “Pompeii,” a 2003 thriller by Robert Harris that is based on the real-life eruption of Mount Vesuvius in ancient Italy. “The story follows a protagonist, who is outside the city of Pompeii and notices steam and strange things happening around the volcano,” Berns says. “He tries to get back to Pompeii in time to save the woman he loves. Meanwhile, the volcano continues to bubble and nobody in the city recognizes the signs.”
The researchers chose the book due to its page-turning plot. “It depicts true events in a fictional and dramatic way,” Berns says. “It was important to us that the book had a strong narrative line.”
For the first five days, the participants came in each morning for a base-line fMRI scan of their brains in a resting state. Then they were given nine sections of the novel, about 30 pages each, over a nine-day period. They were asked to read the assigned section in the evening, and come in the following morning. After taking a quiz to ensure they had finished the assigned reading, the participants underwent an fMRI scan of their brain in a non-reading, resting state. After completing all nine sections of the novel, the participants returned for five more mornings to undergo additional scans in a resting state.
The results showed heightened connectivity in the left temporal cortex, an area of the brain associated with receptivity for language, on the mornings following the reading assignments. “Even though the participants were not actually reading the novel while they were in the scanner, they retained this heightened connectivity,” Berns says. “We call that a ‘shadow activity,’ almost like a muscle memory.”
Heightened connectivity was also seen in the central sulcus of the brain, the primary sensory motor region of the brain. Neurons of this region have been associated with making representations of sensation for the body, a phenomenon known as grounded cognition. Just thinking about running, for instance, can activate the neurons associated with the physical act of running.
“The neural changes that we found associated with physical sensation and movement systems suggest that reading a novel can transport you into the body of the protagonist,” Berns says. “We already knew that good stories can put you in someone else’s shoes in a figurative sense. Now we’re seeing that something may also be happening biologically.”
The neural changes were not just immediate reactions, Berns says, since they persisted the morning after the readings, and for the five days after the participants completed the novel.
“It remains an open question how long these neural changes might last,” Berns says. “But the fact that we’re detecting them over a few days for a randomly assigned novel suggests that your favorite novels could certainly have a bigger and longer-lasting effect on the biology of your brain.”
New study reveals insight into how the brain processes shape and color
A new study by Wellesley College neuroscientists is the first to directly compare brain responses to faces and objects with responses to colors. The paper, by Bevil Conway, Wellesley Associate Professor of Neuroscience, and Rosa Lafer-Sousa, a 2009 Wellesley graduate currently studying in the Brain and Cognitive Sciences program at MIT, reveals new information about how the brain’s inferior temporal cortex processes information.
Located at the base of the brain, the inferior temporal cortex (IT) is a large expanse of tissue that has been shown to be critical for object perception. This region of the brain is commonly divided into posterior, central, and anterior parts, but it remains unclear as to whether these partitions constitute distinct areas. An existing, popular theory is that the parts represent a hierarchical organization of information processing, a notion that has previously been supported by functional magnetic resonance imaging (fMRI) in monkeys. For their study, Conway and Lafer-Sousa used non-invasive fMRI to measure responses across the brains of rhesus monkeys to a range of different stimuli and obtained responses to images of objects, faces, places and colored stripes. “The technique enabled us to determine the spatial distribution of responses across the brain, and has been useful in figuring out how the visual brain is organized,” Conway said.
Conway, a visual neuroscientist and artist, examines the way the nervous system processes color using physiological, behavioral, and modeling techniques. Conway and Lafer-Sousa assert that color provides a useful tool for tackling questions about processing in the IT region, as it has little “low-level” feature similarity with shapes (psychological work shows that color can be perceived independent of shape)—therefore any relationship between color-responsive and shape-responsive regions should reflect fundamental organizational principles.
"Shape and color are both properties of objects and are processed by the parts of the brain known to be important for detecting and discriminating objects. However, the way this part of brain is organized has not been clear, for example, is color computed by different parts of this region than those that compute shape?" The answer to this question, Conway said, has deep implications for understanding the general computational principles used by the brain and how the brain evolved.
"Our work showed that, to a large extent, color and faces are handled by separate, parallel streams, and that these pieces of information are processed by connected, serial stages," Conway said. "One can imagine the processing as an assembly line, where some aspect of faces – and some aspect of color – is computed first. The output is then sent to another region downstream that makes a subsequent computation."
They hypothesized that the earliest stages in color processing involve detecting and discriminating hue, while the later stages compute color-memory association. For example, the brain may first compute that yellow is diagnostic of banana, then later, color categories are recognized; for example, limes, grass, and fern leaves are all “green.”
"The most striking aspect of the study is what it reveals about the precision of the organization of the brain. We often think that because the brain consists of billions of neurons, that at some level it must be quite variable how the neurons are organized," Conway said. "The study shows that there is a remarkable precision in organization of the neural circuits for high-level vision, which will make tractable many questions bridging cognitive science and systems neuroscience."
As a visual artist, Conway said the aspect of the research he finds most satisfying is the beauty of the organizational patterns that, he said, are “clearly are the result of a set of underlying organizational principles.” He continued, “It is interesting to think that the brain reflects what artists have long recognized: that color and shape can be decoupled, each represented somewhat independently—think of color monochromes versus black-and-white line drawings. The neural architecture provides a reason why this is effective or possible.”
The researchers note that it remains unclear whether the organizational principles found in humans apply to monkeys, an important issue that bears on cortical evolution. However, their results suggest that the IT comprises parallel, multi-stage processing networks subject to one organizing principle.
Musical brain-reading sheds light on neural processing of music
Finnish and Danish researchers have developed a new method that performs decoding, or brain-reading, during continuous listening to real music. Based on recorded brain responses, the method predicts how certain features related to tone color and rhythm of the music change over time, and recognizes which piece of music is being listened to. The method also allows pinpointing the areas in the brain that are most crucial for the processing of music. The study was published in the journal NeuroImage.
Using functional magnetic resonance imaging (fMRI), the research team at the Finnish Centre of Excellence in Interdisciplinary Music Research in the Universities of Jyväskylä and Helsinki, and the Center for Functionally Integrative Neuroscience in Aarhus University, Denmark, recorded the brain responses of participants while they were listening to a 16-minute excerpt of the album Abbey Road by the Beatles. Following this, they used computational algorithms to extract a collection of musical features from the musical recording. Subsequently, they employed a collection of machine-learning methods to train a computer model that predicts how the features of the music change over time. Finally, they develop a classifier that predicts which part of the music the participant was listening to at each time.
The researchers found that most of the musical features included in the study could be reliably predicted from the brain data. They also found that the piece being listened to could be predicted significantly better than chance. Fairly large differences were however found between participants in terms of the prediction accuracy. An interesting finding was that areas outside of the auditory cortex, including motor, limbic, and frontal areas, had to be included in the models to obtain reliable predictions, providing thus evidence for the important role of these areas in the processing of musical features.
"We believe that decoding provides a method that complements other existing methods to obtain more reliable information about the complex processing of music in the brain", says Professor Petri Toiviainen from the University of Jyväskylä. "Our results provide additional evidence for the important involvement of emotional and motor areas in music processing."
(Source: jyu.fi)
Brain connections may explain why girls mature faster
Newcastle University scientists have discovered that as the brain re-organises connections throughout our life, the process begins earlier in girls which may explain why they mature faster during the teenage years.
As we grow older, our brains undergo a major reorganisation reducing the connections in the brain. Studying people up to the age of 40, scientists led by Dr Marcus Kaiser and Ms Sol Lim at Newcastle University found that while overall connections in the brain get streamlined, long-distance connections that are crucial for integrating information are preserved.
The researchers suspect this newly-discovered selective process might explain why brain function does not deteriorate – and indeed improves –during this pruning of the network. Interestingly, they also found that these changes occurred earlier in females than in males.
Explaining the work which is being published in Cerebral Cortex, Dr Kaiser, Reader in Neuroinformatics at Newcastle University, says: “Long-distance connections are difficult to establish and maintain but are crucial for fast and efficient processing. If you think about a social network, nearby friends might give you very similar information – you might hear the same news from different people. People from different cities or countries are more likely to give you novel information. In the same way, some information flow within a brain module might be redundant whereas information from other modules, say integrating the optical information about a face with the acoustic information of a voice is vital in making sense of the outside world.”
Brain “pruned”
The researchers at Newcastle, Glasgow and Seoul Universities evaluated the scans of 121 healthy participants between the ages of 4 and 40 years as this is where the major connectivity changes can be seen during this period of maturation and improvement in the brain. The work is part of the EPSRC-funded Human Green Brain project which examines human brain development.
Using a non-invasive technique called diffusion tensor imaging – a special measurement protocol for Magnetic Resonance Imaging (MRI) scanners – they demonstrated that fibres are overall getting pruned that period.
However, they found that not all projections (long-range connections) between brain regions are affected to the same extent; changes were influenced differently depending on the types of connections.
Projections that are preserved were short-cuts that quickly link different processing modules, e.g. for vision and sound, and allow fast information transfer and synchronous processing. Changes in these connections have been found in many developmental brain disorders including autism, epilepsy and schizophrenia.
The researchers have demonstrated for the first time that the loss of white matter fibres between brain regions is a highly selective process – a phenomenon they call preferential detachment. They show that connections between distant brain regions, between brain hemispheres, and between processing modules lose fewer nerve fibres during brain maturation than expected. The researchers say this may explain how we retain a stable brain network during brain maturation.
Commenting on the fact that these changes occurred earlier in females than males, Ms Sol Lim explains: “The loss of connectivity during brain development can actually help to improve brain function by reorganizing the network more efficiently. Say instead of talking to many people at random, asking a couple of people who have lived in the area for a long time is the most efficient way to know your way. In a similar way, reducing some projections in the brain helps to focus on essential information.”
(Source: ncl.ac.uk)
Contrast Agent Linked with Brain Abnormalities on MRI
For the first time, researchers have confirmed an association between a common magnetic resonance imaging (MRI) contrast agent and abnormalities on brain MRI, according to a new study published online in the journal Radiology. The new study raises the possibility that a toxic component of the contrast agent may remain in the body long after administration.
Brain MRI exams are often performed with a gadolinium-based contrast medium (Gd-CM). Gadolinium’s paramagnetic properties make it useful for MRI, but the toxicity of the gadolinium ion means it must be chemically bonded with non-metal ions so that it can be carried through the kidneys and out of the body before the ion is released in tissue. Gd-CM is considered safe in patients with normal kidney function.
However, in recent years, clinicians in Japan noticed that patients with a history of multiple administrations of Gd-CM showed areas of high intensity, or hyperintensity, on MRI in two brain regions: the dentate nucleus (DN) and globus pallidus (GP). The precise clinical ramifications of hyperintensity are not known, but hyperintensity in the DN has been associated with multiple sclerosis, while hyperintensity of the GP is linked with hepatic dysfunction and several diseases.
To learn more, the researchers compared unenhanced T1-weighted MR images (T1WI) of 19 patients who had undergone six or more contrast-enhanced brain scans with 16 patients who had received six or fewer unenhanced scans. The hyperintensity of both the DN and the GP correlated with the number of Gd-CM administrations.
"Hyperintensity in the DN and GP on unenhanced MRI may be a consequence of the number of previous Gd-CM administrations," said lead author Tomonori Kanda, M.D., Ph.D., from Teikyo University School of Medicine in Tokyo and the Hyogo Cancer Center in Akashi, Japan. "Because gadolinium has a high signal intensity in the body, our data may suggest that the toxic gadolinium component remains in the body even in patients with normal renal function."
Dr. Kanda noted that because patients with multiple sclerosis tend to undergo numerous contrast-enhanced brain MRI scans, the hyperintensity of the DN seen in these patients may have more to do with the large cumulative gadolinium dose than the disease itself.
The mechanisms by which Gd-CM administration causes hyperintensity of the DN and GP remain unclear, Dr. Kanda said. Previous studies on animals and humans have shown that the ion can be retained in bone and tissue for several days or longer after administration.
"The hyperintensity of DN and GP on unenhanced T1WI may be due to gadolinium deposition in the brain independent of renal function, and the deposition may remain in the brain for a long time," Dr. Kanda suggested.
Dr. Kanda emphasized that there is currently no proof that gadolinium is responsible for hyperintensity on brain MRI. Further research based on autopsy specimens and animal experiments will be needed to clarify the relationship and determine if the patients with MRI hyperintensity in their brains have symptoms.
"Because patients who have multiple contrast material injections tend to have severe diseases, a slight symptom from the gadolinium ion may be obscured," Dr. Kanda said.
There are two types of Gd-CM , linear and macrocyclic, with distinct chemical compositions. Since the patients in the study received only the linear type, additional research is needed to see if the macrocyclic type can prevent MRI hyperintensity, according to Dr. Kanda.
Brain Chemical Ratios Help Predict Developmental Delays in Preterm Infants
Researchers have identified a potential biomarker for predicting whether a premature infant is at high risk for motor development problems, according to a study published online in the journal Radiology.
"We are living in an era in which survival of premature birth is more common," said Giles S. Kendall, Ph.D., consultant for the neonatal intensive care unit at University College London Hospitals NHS Foundation Trust and honorary senior lecturer of neonatal neuroimaging and neuroprotection at the University College London. "However, these infants continue to be at risk for neurodevelopmental problems."
Patients in the study included 43 infants (24 male) born at less than 32 weeks gestation and admitted to the neonatal intensive care unit (NICU) at the University College of London between 2007 and 2010. Dr. Kendall and his research team performed magnetic resonance imaging (MRI) and MR spectroscopy (MRS) exams on the infants at their approximate expected due dates (or term-equivalent age). MRS measures chemical levels in the brain.
The imaging studies were focused on the white matter of the brain, which is composed of nerve fibers that connect the functional centers of the brain.
"The white matter is especially fragile in the newborn and at risk for injury," Dr. Kendall explained.
One year later, 40 of the 43 infants were evaluated using the Bayley Scales of Infant and Toddler Development, which assess fine motor, gross motor and communication abilities. Of the 40 infants evaluated, 15 (38 percent) had abnormal composite motor scores and four (10 percent) showed cognitive impairment.
Statistical analysis of the MRS results and Bayley Scales scores revealed that the presence of two chemical ratios—increased choline/creatine (Cho/Cr) and decreased N-acetylaspartate/choline (NAA/Cho)—at birth were significantly correlated with developmental delays one year later.
"Low N-acetylaspartate/choline and rising choline/creatine observed during MRS at the baby’s expected due date predicted with 70 percent certainty which babies were at high risk for motor development problems at one year," Dr. Kendall said.
Dr. Kendall said a tool to predict the likelihood of a premature baby having neurodevelopmental problems would be useful in determining which infants should receive intensive interventions and in testing the effectiveness of those therapies.
"Physiotherapy interventions are available but are very expensive, and the vast majority of premature babies don’t need them," Dr. Kendall said. "Our hope is to find a robust biomarker that we can use as an outcome measure so that we don’t have to wait five or six years to see if an intervention has worked."
Dr. Kendall said severe disability associated with premature births has decreased over the past two decades as a result of improved care techniques in the NICU. However, many premature infants today have subtle abnormalities that are difficult to detect with conventional MRI.
"There’s a general shift away from simply ensuring the survival of these infants to how to give them the best quality of life," he said. "Our research is part of an effort to improve the outcomes for prematurely born infants and to identify earlier which babies are at greater risk."
‘Chemobrain’ linked to disrupted brain networks
For some cancer patients, the mental fogginess that develops with chemotherapy lingers long after treatment ends. Now research in breast cancer patients may offer an explanation.
Patients who experience “chemobrain” following treatment for breast cancer show disruptions in brain networks that are not present in patients who do not report cognitive difficulties, according to researchers at Washington University School of Medicine in St. Louis.
Results of the small study were reported Thursday, Dec. 12 at a poster presentation at the San Antonio Breast Cancer Symposium.
According to the researchers, many breast cancer patients who receive chemotherapy report long-term problems with memory, attention, learning, visual-spatial skills and other forms of information processing. The brain mechanisms contributing to these difficulties are poorly understood.
The investigators used an imaging technique called resting state functional-connectivity magnetic resonance imaging (rs-fcMRI) to assess the wiring among regions of the brain in 28 patients treated at Siteman Cancer Center at Barnes-Jewish Hospital and Washington University. Fifteen patients reported they were “extremely” or “strongly” affected by cognitive difficulties. The remaining 13 reported no cognitive impairment.
The imaging studies suggest that standard chemotherapy given to breast cancer patients may alter connectivity in brain networks, especially in the frontal parietal control regions responsible for executive function, attention and decision-making.
“Chemobrain is most likely a global phenomenon in the brain, but a set of regions involved in executive control, called the frontal-parietal network, is perhaps the most affected brain system,” said Jay F. Piccirillo, MD, professor of otolaryngology and a member of the research team with expertise in the use of brain imaging to study tinnitus, or phantom noise. “We’re confirming previous studies that also have shown this. And we’re developing a solid multidisciplinary working group at Washington University to determine how we can help these women.”
Other studies also have used neuroimaging techniques to observe the neural disruptions associated with Alzheimer’s disease, depression and stroke. Washington University researchers are beginning to investigate whether cancer patients experiencing chemobrain may benefit from therapies similar to those that help patients with other cognitive disorders.
(Source: news.wustl.edu)