Neuroscience

Article Date: 03 Feb 2012 - 0:00 PST

We all know that it can take a little while for our hearing to bounce back after listening to our iPods too loud or attending a raucous concert. But new research at the University of Michigan Health System suggests over-exposure to noise can actually cause more lasting changes to our auditory circuitry - changes that may lead to tinnitus, commonly known as ringing in the ears.

U-M researchers previously demonstrated that after hearing damage, touch-sensing “somatosensory” nerves in the face and neck can become overactive, seeming to overcompensate for the loss of auditory input in a way the brain interprets - or “hears” - as noise that isn’t really there.

The new study, which appears in The Journal of Neuroscience, found that somatosensory neurons maintain a high level of activity following exposure to loud noise, even after hearing itself returns to normal.

The findings were made in guinea pigs, but mark an important step toward potential relief for people plagued by tinnitus, says lead investigator Susan E. Shore, Ph.D., of U-M’s Kresge Hearing Research Institute and a professor of otolaryngology and molecular and integrative physiology at the U-M Medical School.

“The animals that developed tinnitus after a temporary loss in their hearing after loud noise exposure were the ones who had sustained increases in activity in these neural pathways,” Shore says. “In the future it may be possible to treat tinnitus patients by dampening the hyperactivity by reprogramming these auditory-touch circuits in the brain.”

In normal hearing, a part of the brain called the dorsal cochlear nucleus is the first stop for signals arriving from the ear via the auditory nerve. But it’s also a hub where “multitasking” neurons process other sensory signals, such as touch, together with hearing information.

During hearing loss, the other sensory signals entering the dorsal cochlear nucleus are amplified, Shore’s earlier research found. This overcompensation by the somatosensory neurons, which carry information about touch, vibration, skin temperature and pain, is believed to fuel tinnitus in many cases.

Tinnitus affects up to 50 million people in the United States and millions more worldwide, according to the American Tinnitus Association. It can range from intermittent and mildly annoying to chronic, severe and debilitating. There is no cure.

It especially affects baby boomers, who, as they reach an age at which hearing tends to diminish, increasingly find that tinnitus moves in. The condition most commonly occurs with hearing loss, but can also follow head and neck trauma, such as after an auto accident, or dental work. Tinnitus is the number one disability afflicting members of the armed forces.

The involvement of touch sensing (or “somatosensory”) nerves in the head and neck explains why many tinnitus sufferers can change the volume and pitch of the sound by clenching their jaw, or moving their head and neck, Shore explains.

While the new study builds on previous discoveries by Shore and her team, many aspects are new.

“This is the first research to show that, in the animals that developed tinnitus after hearing returned to normal, increased excitation from the somatosensory nerves in the head and neck continued. This dovetails with our previous research, which suggests this somatosensory excitation is a major component of tinnitus,” says Shore, who serves on the scientific advisory committee of the American Tinnitus Association.

“The better we understand the underlying causes of tinnitus, the better we’ll be able to develop new treatments,” she adds.

Source: Medical News Today 

Article Date: 03 Feb 2012 - 0:00 PST

For Bradley Duchaine, there is definitely more than meets the eye where faces are concerned.

With colleagues at Birkbeck College in the University of London, he is investigating the process of facial recognition, seeking to understand the complexity of what is actually taking place in the brain when one person looks at another.

His studies target people who display an inability to recognize faces, a condition long known as prosopagnosia. Duchaine is trying to understand the neural basis of the condition while also make inferences about what is going wrong in terms of information processing - where in the stages that our brains go through to recognize a face is the system breaking down. A paper published in Brain details the most recent experimental results.

“We refer to prosopagnosia as a ‘selective’ deficit of face recognition, in that other cognitive process do not seem to be affected,” explains Duchaine, an associate professor of psychological and brain sciences. “[People with the condition] might be able to recognize voices perfectly, which demonstrates that it is really a visual problem. In what we call pure cases, people can recognize cars perfectly, and they can recognize houses perfectly. It is just faces that are a problem.”

The condition may be acquired as the result of a stroke, for example. But in the recent study, Duchaine focused on developmental prosopagnosia, in which a person fails to develop facial recognition abilities.

“Other parts of the brain develop apparently normally,” Duchaine says. “These are intelligent people who have good jobs and get along fine but they can’t recognize faces.”

The primary experimental tool in this experiment was the electroencephalogram (EEG), which has the advantage of providing excellent temporal resolution - pinpointing the timing of the brain’s electrical response to a given stimulus.

Duchaine and his colleagues placed a series of electrodes around the scalps of prosopagnosics and showed them images of famous faces and non-famous faces, recording their responses. As expected, many of the famous faces were not recognized.

They found an electrical response at about 250 milliseconds (ms) after seeing the faces. Among the control group of non-prosopagnosics, a real difference was observed between their responses to famous and non-famous faces. In half the prosopagnosics there was not. Surprisingly, however, in the other half of the prosopagnosic test subjects they did find a difference.

“On the many trials where half failed to categorize a famous face as familiar, they nevertheless showed an EEG difference around 250ms after stimulus presentation between famous and non-famous faces like normal subjects do. Normal subjects also show a difference between famous and non-famous about 600ms after presentation, but the prosopagnosics did not show this difference,” Duchaine observes.

This pattern of results suggests the prosopagnosics unconsciously recognized the famous faces at an early stage (250ms) but this information was lost by the later stage (600ms). Duchaine concludes that even though they are not consciously aware that this is a famous face, some part of their brain at this stage in the process is aware and is recognizing that face, a phenomenon termed covert face recognition.

He suggests that the other half of the prosopagnosics, who showed no difference between responses at 250ms, were experiencing a malfunction in their face processing system already at this early stage suggesting a different type of prosopagnosia.

“The temporal lobe contains a number of face processing areas, so you can imagine there are many different ways that this system can malfunction. Not only can an area not work, connections between areas might not work yielding probably dozens of these different variants of this condition,” he surmises.

Covert recognition has been demonstrated in prosopagnosia acquired through brain damage, but Duchaine’s work is the first convincing demonstration of covert recognition in developmental prosopagnosia, the much more common form. 

Source: Medical News Today

ScienceDaily (Feb. 2, 2012) — One of the most distinctive signs of the development of Alzheimer’s disease is a change in the behavior of a protein that neuroscientists call tau. In normal brains, tau is present in individual units essential to neuron health. In the cells of Alzheimer’s brains, by contrast, tau proteins aggregate into twisted structures known as “neurofibrillary tangles.” These tangles are considered a hallmark of the disease, but their precise role in Alzheimer’s pathology has long been a point of contention among researchers.

Now, University of Texas Medical Branch at Galveston researchers have found new evidence that confirms the significance of tau to Alzheimer’s. Instead of focusing on tangles, however, their work highlights the intermediary steps between a single tau protein unit and a neurofibrillary tangle — assemblages of two, three, four, or more tau proteins known as “oligomers,” which they believe are the most toxic entities in Alzheimer’s.

"What we discovered is that there are smaller structures that form before the neurofibrillary tangles, and they are much more toxic than the big structures," said Rakez Kayed, UTMB assistant professor and senior author of a paper on the work now online in the FASEB Journal. “And we established that they were toxic in real human brains, which is important to developing an effective therapy.”

According to Kayed, a key antibody developed at UTMB called T22 enabled the team to produce a detailed portrait of tau oligomer behavior in human brain tissue. Specifically designed to bond only to tau oligomers (and not lone tau proteins or neurofibrillary tangles), the antibody made it possible for the researchers to use a variety of analytical tools to compare samples of Alzheimer’s brain with samples of age-matched healthy brain.

"One thing that’s remarkable about this research is that before we developed this antibody, people couldn’t even see tau oligomers in the brain," Kayed said. "With T22, we were able to thoroughly characterize them, and also study them in human brain cells."

Among the researchers’ most striking findings: in some of the Alzheimer’s brains they examined, tau oligomer levels were as much as four times as high as those found in age-matched control brains.

Other experiments revealed specific biochemical behavior and structures taken on by oligomers, and demonstrated their presence outside neurons — in particular, on the walls of blood vessels.

"We think this is going to make a big impact scientifically, because it opens up a lot of new areas to study," Kayed said. "It also relates to our main focus, developing a cure for Alzheimer’s. And I find that very, very exciting."

Provided by University of Texas Medical Branch at Galveston

Source: ScienceDaily

Article Date: 02 Feb 2012 - 1:00 PST

Holding information within one’s memory for a short while is a seemingly simple and everyday task. We use our short-term memory when remembering a new telephone number if there is nothing to write at hand, or to find the beautiful dress inside the store that we were just admiring in the shopping window. Yet, despite the apparent simplicity of these actions, short-term memory is a complex cognitive act that entails the participation of multiple brain regions. However, whether and how different brain regions cooperate during memory has remained elusive. A group of researchers from the Max Planck Institute for Biological Cybernetics in Tubingen, Germany have now come closer to answering this question. They discovered that oscillations between different brain regions are crucial in visually remembering things over a short period of time.

It has long been known that brain regions in the frontal part of the brain are involved in short-term memory, while processing of visual information occurs primarily at the back of the brain. However, to successfully remember visual information over a short period of time, these distant regions need to coordinate and integrate information.

To better understand how this occurs, scientists from the Max Planck Institute of Biological Cybernetics in the department of Nikos Logothetis recorded electrical activity both in a visual area and in the frontal part of the brain in monkeys. The scientists showed the animals identical or different images within short intervals while recording their brain activity. The animals then had to indicate whether the second image was the same as the first one.

The scientists observed that, in each of the two brain regions, brain activity showed strong oscillations in a certain set of frequencies called the theta-band. Importantly, these oscillations did not occur independently of each other, but synchronized their activity temporarily: “It is as if you have two revolving doors in each of the two areas. During working memory, they get in sync, thereby allowing information to pass through them much more efficiently than if they were out of sync,” explains Stefanie Liebe, the first author of the study, conducted in the team of Gregor Rainer in cooperation with Gregor Hörzer from the Technical University Graz. The more synchronized the activity was, the better could the animals remember the initial image. Thus, the authors were able to establish a direct relationship between what they observed in the brain and the performance of the animal.

The study highlights how synchronized brain oscillations are important for the communication and interaction of different brain regions. Almost all multi-faceted cognitive acts, such as visual recognition, arise from a complex interplay of specialized and distributed neural networks. How relationships between such distributed sites are established and how they contribute to represent and communicate information about external and internal events in order to attain a coherent percept or memory is still poorly understood.

Source: Medical News Today

February 1st, 2012 in Psychology & Psychiatry 

These are examples of famous faces and non-famous faces used in Bradley Duchaine’s prosopagnosia experiment. Paired famous and non-famous faces are shown in corresponding positions. Credit: Bradley Duchaine

For Bradley Duchaine, there is definitely more than meets the eye where faces are concerned.

With colleagues at Birkbeck College in the University of London, he is investigating the process of facial recognition, seeking to understand the complexity of what is actually taking place in the brain when one person looks at another.

His studies target people who display an inability to recognize faces, a condition long known as prosopagnosia. Duchaine is trying to understand the neural basis of the condition while also make inferences about what is going wrong in terms of information processing-where in the stages that our brains go through to recognize a face is the system breaking down. A paper published in Brain details the most recent experimental results.

"We refer to prosopagnosia as a ‘selective’ deficit of face recognition, in that other cognitive process do not seem to be affected," explains Duchaine, an associate professor of psychological and brain sciences. "[People with the condition] might be able to recognize voices perfectly, which demonstrates that it is really a visual problem. In what we call pure cases, people can recognize cars perfectly, and they can recognize houses perfectly. It is just faces that are a problem."

The condition may be acquired as the result of a stroke, for example. But in the recent study, Duchaine focused on developmental prosopagnosia, in which a person fails to develop facial recognition abilities.

"Other parts of the brain develop apparently normally," Duchaine says. "These are intelligent people who have good jobs and get along fine but they can’t recognize faces."

The primary experimental tool in this experiment was the electroencephalogram (EEG), which has the advantage of providing excellent temporal resolution-pinpointing the timing of the brain’s electrical response to a given stimulus.

Duchaine and his colleagues placed a series of electrodes around the scalps of prosopagnosics and showed them images of famous faces and non-famous faces, recording their responses. As expected, many of the famous faces were not recognized.

They found an electrical response at about 250 milliseconds (ms) after seeing the faces. Among the control group of non-prosopagnosics, a real difference was observed between their responses to famous and non-famous faces. In half the prosopagnosics there was not. Surprisingly, however, in the other half of the prosopagnosic test subjects they did find a difference.

"On the many trials where half failed to categorize a famous face as familiar, they nevertheless showed an EEG difference around 250ms after stimulus presentation between famous and non-famous faces like normal subjects do. Normal subjects also show a difference between famous and non-famous about 600ms after presentation, but the prosopagnosics did not show this difference," Duchaine observes.

This pattern of results suggests the prosopagnosics unconsciously recognized the famous faces at an early stage (250ms) but this information was lost by the later stage (600ms). Duchaine concludes that even though they are not consciously aware that this is a famous face, some part of their brain at this stage in the process is aware and is recognizing that face, a phenomenon termed covert face recognition.

He suggests that the other half of the prosopagnosics, who showed no difference between responses at 250ms, were experiencing a malfunction in their face processing system already at this early stage suggesting a different type of prosopagnosia.

"The temporal lobe contains a number of face processing areas, so you can imagine there are many different ways that this system can malfunction. Not only can an area not work, connections between areas might not work yielding probably dozens of these different variants of this condition," he surmises.

Covert recognition has been demonstrated in prosopagnosia acquired through brain damage, but Duchaine’s work is the first convincing demonstration of covert recognition in developmental prosopagnosia, the much more common form.

Provided by Dartmouth College

"Just another pretty face: Professor investigates neural basis of prosopagnosia." February 1st, 2012. http://medicalxpress.com/news/2012-02-pretty-professor-neural-basis-prosopagnosia.html

February 1st, 2012 in Physics / General Physics 

Scientists have found that the capacity of the human brain to process and record information - and not economic constraints - may constitute the dominant limiting factor for the overall growth of globally stored information. These findings have just been published in an article in EPJ B by Claudius Gros and colleagues from the Institute for Theoretical Physics at Goethe University Frankfurt in Germany.

The authors first looked at the distribution of 633 public internet files by plotting the number of videos, audio and image files against the size of the files. They gathered files which were produced by humans or intended for human use with the spider file search engine Findfiles.net. They chose to focus on files which are hosted on domains pointing from the online encyclopaedia Wikipedia and the open web directory dmoz.

Assuming that economic costs for data production are proportional to the amount of data produced, these costs should be driving the generation of information exponentially. However, the authors found that, in fact, economic costs were not the limiting factors for data production. The absence of exponential tails for the graph representing the number of files indicates this conclusion.

They found that underlying neurophysiological processes influence the brain’s ability to handle information. For example, when a person produces an image and attributes a subjective value to it, for example, a given resolution, he or she is influenced by his or her perception of the quality of that image. Their perception of the amount of information gained when increasing the resolution of a low-quality image is substantially higher than when increasing the resolution of a high-quality photo by the same degree. This relation is known as the Weber-Fechner law.

The authors observed that file-size distributions obey this Weber-Fechner law. This means that the total amount of information cannot grow faster than our ability to digest or handle it.

More information: Gros C., Kaczor G., Markovic D., (2012) Neuropsychological constraints to human data production on a global scale, European Physical Journal B (EPJ B) 85: 28, DOI 10.1140/epjb/e2011-20581-3

Provided by Springer

"Brain capacity limits exponential online data growth." February 1st, 2012.http://www.physorg.com/news/2012-02-brain-capacity-limits-exponential-online.html