Posts tagged neuroscience

Vivid hallucinations experienced by people with sight loss last far longer and have more serious consequences than previously thought, according to new research from King’s College London and the Macular Society. 

The study is the largest survey of the phenomenon, known as Charles Bonnet Syndrome, and documented the experiences of 492 visually impaired people who had experienced visual hallucinations. The findings, published in the British Journal of Ophthalmology, show there is a serious discrepancy between medical opinion and the realities of the condition.

Charles Bonnet Syndrome is widely considered by the medical profession to be benign and short-lived. However, the new research shows that 80% of respondents had hallucinations for five years or more and 32% found them predominantly unpleasant, distressing and negative. 

The study described this group of people as having “negative outcome Charles Bonnet Syndrome”. The group was more likely to have frequent, fear inducing, longer duration hallucinations, which affected daily activities. They were more likely to attribute hallucinations to serious mental illness and were less likely to have been warned about the possibility of hallucinations before they started. 

Of respondents, 38% regarded their hallucinations as startling, terrifying or frightening when they first occurred and 46% said hallucinations had an effect on their ability to complete daily tasks. 36% of people who discussed the issue with a medical professional said the professional was “unsure or did not know” about the diagnosis.

Dr Dominic ffytche, who led the research at the Institute of Psychiatry at King’s, says:  “Charles Bonnet Syndrome has been traditionally thought of as benign. Indeed, it has been questioned whether it should even be considered a medical condition given it does not cause problems and goes away by itself. The results of our survey paint a very different picture.

“With no specific treatments for Charles Bonnet Syndrome, the survey highlights the importance of raising awareness to reduce the distress it causes, particularly before symptoms start. All people with Charles Bonnet Syndrome are relieved or reassured to find out about the cause of their hallucinations and our evidence shows the knowledge may help reduce negative outcome.”

People with macular disease are particularly prone to Charles Bonnet hallucinations. They are thought to be a reaction of the brain to the loss of visual stimulation. More than half of people with severe sight loss experience them but many do not tell others for fear they will be thought to have a serious mental illness. 

Age-related macular (AMD) degeneration affects the central vision and is the most common cause of sight loss in the UK. Nearly 600,000 people have late-stage AMD today and more people will become affected as our population ages. Around half will have hallucinations at some stage. 

Tony Rucinski, Chief Executive, the Macular Society, said: “It is essential that people affected by sight loss are given information about Charles Bonnet Syndrome at diagnosis or as soon after as possible. 

“Losing your sight is bad enough without the fear that you have something like dementia as well. We need medical professionals to recognise the seriousness of Charles Bonnet Syndrome and ensure that people don’t suffer unnecessarily. More research is also needed to investigate Charles Bonnet Syndrome and possible ways of reducing its impact.”

Dr ffytche is also leading a large NIHR funded research programme on visual hallucinations to develop a much-needed evidence base to inform NHS practice in managing and treating the symptoms. 

Most schools across the United States provide simple vision tests to their students—not to prescribe glasses, but to identify potential problems and recommend a trip to the optometrist. Researchers are now on the cusp of providing the same kind of service for autism.

Researchers at Duke University have developed software that tracks and records infants’ activity during videotaped autism screening tests. Their results show that the program is as good at spotting behavioral markers of autism as experts giving the test themselves, and better than non-expert medical clinicians and students in training.

The results appear online in the journal Autism Research and Treatment.

“We’re not trying to replace the experts,” said Jordan Hashemi, a graduate student in computer and electrical engineering at Duke. “We’re trying to transfer the knowledge of the relatively few autism experts available into classrooms and homes across the country. We want to give people tools they don’t currently have, because research has shown that early intervention can greatly impact the severity of the symptoms common in autism spectrum disorders.”

The study focused on three behavioral tests that can help identify autism in very young children.

In one test, an infant’s attention is drawn to a toy being shaken on the left side and then redirected to a toy being shaken on the right side. Clinicians count how long it takes for the child’s attention to shift in response to the changing stimulus. The second test passes a toy across the infant’s field of view and looks for any delay in the child tracking its motion. In the last test, a clinician rolls a ball to a child and looks for eye contact afterward—a sign of the child’s engagement with their play partner.

In all of the tests, the person administering them isn’t just controlling the stimulus, he or she is also counting how long it takes for the child to react—an imprecise science at best. The new program allows testers to forget about taking measurements while also providing more accuracy, recording reaction times down to tenths of a second.

“The great benefit of the video and software is for general practitioners who do not have the trained eye to look for subtle early warning signs of autism,” said Amy Esler, an assistant professor of pediatrics and autism researcher at the University of Minnesota, who participated in some of the trials highlighted in the paper.

“The software has the potential to automatically analyze a child’s eye gaze, walking patterns or motor behaviors for signs that are distinct from typical development,” Esler said. “These signs would signal to doctors that they need to refer a family to a specialist for a more detailed evaluation.”

According to Hashemi and his adviser, Guillermo Sapiro, professor of electrical and computer engineering and biomedical engineering at Duke, because the program is non-invasive, it could be useful immediately in homes and clinics. Neither, however, expects it to become widely used—not because clinicians, teachers and parents aren’t willing, but because the researchers are working on an even more practical solution.

Later this year, the Duke team (which includes students and faculty from engineering and psychiatry) plans to test a new tablet application that could do away with the need for a person to administer any tests at all. The program would watch for physical and facial responses to visual cues played on the screen, analyze the data and automatically report any potential red flags. Any parent, teacher or clinician would simply need to download the app and sit their child down in front of it for a few minutes.

The efforts are part of the Information Initiative at Duke, which connects researchers from disparate fields to experts in computer programming to help analyze large data sets.

“We’re currently working with autism experts at Duke Medicine to determine what sorts of easy tests could be used on just a computer or tablet screen to spot any potential concerns,” said Sapiro. “The goal is to mimic the same sorts of social interactions that the tests with the toys and balls measure, but without the toys and balls. The research has shown that the earlier autism can be spotted, the more beneficial intervention can be. And we want to provide everyone in the world with the ability to spot those signs as early as possible.”

(Source: pratt.duke.edu)

A type of retina cell plays a more critical role in vision than previously known, a team led by Johns Hopkins University researchers has discovered.

Working with mice, the scientists found that the ipRGCs – an atypical type of photoreceptor in the retina – help detect contrast between light and dark, a crucial element in the formation of visual images. The key to the discovery is the fact that the cells express melanopsin, a type of photopigment that undergoes a chemical change when it absorbs light.

“We are quite excited that melanopsin signaling contributes to vision even in the presence of functional rods and cones,” postdoctoral fellow Tiffany M. Schmidt said.

Schmidt is lead author of a recently published study in the journal Neuron. The senior author is Samer Hattar, associate professor of biology in the university’s Krieger School of Arts and Sciences. Their findings have implications for future studies of blindness or impaired vision.

Rods and cones are the most well-known photoreceptors in the retina, activating in different light environments. Rods, of which there are about 120 million in the human eye, are highly sensitive to light and turn on in dim or low-light environments. Meanwhile the 6 million to 7 million cones in the eye are less sensitive to light; they drive vision in brighter light conditions and are essential for color detection.

Rods and cones were thought to be the only light-sensing photoreceptors in the retina until about a decade ago when scientists discovered a third type of retinal photoreceptor – the ipRGC, or intrinsically photosensitive retinal ganglion cell – that contains melanopsin. Those cells were thought to be needed exclusively for detecting light for non-image-dependent functions, for example, to control synchronization of our internal biological clocks to daytime and the constriction of our pupils in response to light.

“Rods and cones were thought to mediate vision and ipRGCs were thought to mediate these simple light-detecting functions that happen outside of conscious perception,” Schmidt said. “But our experiments revealed that ipRGCs influence a greater diversity of behaviors than was previously known and actually contribute to an important aspect of image-forming vision, namely contrast detection.”

The Johns Hopkins team along with other scientists conducted several experiments with mice and found that when melanopin was present in the retinal ganglion cells, the mice were better able to see contrast in a Y-shaped maze, known as the visual water task test. In the test, mice are trained to associate a pattern with a hidden platform that allows them to escape the water. Mice that had the melanopsin gene intact had higher contrast sensitivity than mice that lack the gene.

“Melanopsin signaling is essential for full contrast sensitivity in mouse visual functions,” said Hattar. “The ipRGCs and melanopsin determine the threshold for detecting edges in the visual scene, which means that visual functions that were thought to be solely mediated by rods and cones are now influenced by this system. The next step is to determine if melanopsin plays a similar role in the human retina for image-forming visual functions.”

(Source: releases.jhu.edu)

A precise rhythm of electrical impulses transmitted from cells in the inner ear coaches the brain how to hear, according to a new study led by researchers at the University of Pittsburgh School of Medicine. They report the first evidence of this developmental process today in the online version of Neuron.

The ear generates spontaneous electrical activity to trigger a response in the brain before hearing actually begins, said senior investigator Karl Kandler, Ph.D., professor of otolaryngology and neurobiology, Pitt School of Medicine. These patterned bursts start at inner hair cells in the cochlea, which is part of the inner ear, and travel along the auditory nerve to the brain.

"It’s long been speculated that these impulses are intended to ‘wire’ the brain auditory centers," he said. "Until now, however, no one has been able to provide experimental evidence to support this concept."

To map neural connectivity, Dr. Kandler’s team prepared sections of a mouse brain containing the auditory pathways in a chemical that is inert until UV light hits it. Then, they pulsed laser light at a neuron, making the chemical active, which excites the nerve cells to generate an electrical impulse. They then tracked the spread of the impulse to adjacent cells, allowing them to map the network a neuron at a time.

All mice are born unable to hear, a sense that develops around two weeks after birth. But even before hearing starts, the ear produces rhythmic bursts of electrical activity which causes a broad reaction in the brain’s auditory processing centers. As the beat goes on, the brain organizes itself, pruning unneeded connections and strengthening others. To investigate whether the beat is indeed important for this reorganization, the team used genetically engineered mice that lack a key receptor on the inner hair cells which causes them to change their beat.

"In normal mice, the wiring diagram of the brain gets sharper and more efficient over time and they begin to hear," Dr. Kandler said. "But this doesn’t happen when the inner ear beats in a different rhythm, which means the brain isn’t getting the instructions it needs to wire itself correctly. We have evidence that these mice can detect sound, but they have problems perceiving the pitch of sounds."

In humans, such subtle hearing deficits are associated with Central Auditory-Processing Disorders (CAPD), difficulty processing the meaning of sound. About 2 to 3 percent of children are affected with CAPD and these children often have speech and language disorders or delays, and learning disabilities such as dyslexia. In contrast to causes of hearing impairments due to ear deficits, the causes underlying CAPD have remained obscure.

"Our findings suggest that an abnormal rhythm of electrical impulses early in life may be an important contributing factor in the development of CAPD. More research is needed to find out whether this also holds true for humans, but our results point to a new direction that is worth following up," Dr. Kandler said.

(Source: eurekalert.org)

How does a DJ mix two songs to make the beat seem common to both tracks? A successful DJ makes the transition between tracks appear seamless while a bad mix is instantly noticeable and results in a ‘galloping horses’ effect that disrupts the dancing of the crowd. How accurate does beat mixing need to be to enhance, rather than disrupt perceived rhythm?

In a study published today (Wednesday 21 May 2014) in the journal Proceedings of the Royal Society B, scientists from the Universities of Birmingham and Cambridge present a new model that predicts whether or not two tracks will seem to share a common beat. This model also promises to help us understand how groups of people often start moving in synchrony, for example, football fans bouncing up and down at a stadium, or crowds falling into step when walking over a bridge.

‘We found that the time window in which two beat lines are heard as one isn’t fixed - it changes according to the statistical properties of each beat line, including how consistent or predictable they are,’ said Dr Mark Elliott, lead researcher on the study from the University of Birmingham’s School of Psychology. ‘For example, with two very consistent beat lines we only allow a very small time difference between them before we consider them to be separate. By analogy, given that DJs tend to play songs with a strong bass beat, they need to be very accurate in aligning the beats of the two songs if they are to be heard as one so as not to disrupt the flow of dancing. Our model and experiments reveal the timing properties of separate beat lines that determine whether they will be heard as one or two.’

Dr Elliott and his colleagues tested their model using a laboratory task that involved people tapping their fingers in time with two similar beat lines played simultaneously, one defined by high pitched tones, the other low pitched tones. The concurrency of the lines was varied such that the high and low pitched tones were played close together in time or far apart. Furthermore, the separation between the high-low tones was either consistent or randomly varied across the experiment. The researchers determined when people change from tapping along to a single beat formed from the two tones or targeted one of the tones while ignoring the other. They found that the time separation between tones that was required for people to judge them as distinct beats varied according to the consistency of the timings between the tones. Subsequently, these judgments influenced the timing of their movements.

Dr Elliott added, ‘People develop an expectation of when in time the next beat will occur. In defining the beat, they use the separation and consistency of the beat lines to determine whether the two tones should be combined together or whether just one tone should be attended to and the other ignored. Our model was able to predict the timing of participants’ movements based on the timing statistics of the tones we presented. Therefore, it not only allows us to calculate whether two beats will be heard as one, but also means we can predict the subtle effects the perception of an underlying rhythm can have on the movements people make to keep in synchrony with more complex beats.’

Dr Elliott is currently involved in a study, in collaboration with the University of Leeds, investigating the timing accuracy of movements in professional DJs compared to classical musicians and non-musicians. In addition, the findings of the current research are being applied to other areas: ‘We are currently investigating how spontaneous synchronisation of movements occurs within crowds. For example, in football stadiums the crowd sometimes starts to bounce up and down together. When the crowd moves together like this, it can create problems with structural vibration. Working with vibration engineers from the Universities of Sheffield and Exeter, we are applying our models to understand how such crowd dynamics might arise from the way each person adjusts their timing in relation to timing information from the people around them.’

(Source: birmingham.ac.uk)