Researchers identify components of speech recognition pathway in humans

Finding suggests speech perception evolved from animals.


Washington, D.C. — Neuroscientists at Georgetown University Medical Center (GUMC) have defined, for the first time, three different processing stages that a human brain needs to identify sounds such as speech — and discovered that they are the same as ones identified in non-human primates.

In the June 22 issue of the Journal of Neuroscience, the researchers say their discovery — made possible with the help of 13 human volunteers who spent time in a functional MRI machine — could potentially offer important insights into what can go wrong when someone has difficulty speaking, which involves hearing voice-generated sounds, or understanding the speech of others.

But more than that, the findings help shed light on the complex, and extraordinarily elegant, workings of the "auditory" human brain, says Josef Rauschecker, PhD, a professor in the departments of physiology/ biophysics and neuroscience and a member of the Georgetown Institute for Cognitive and Computational Sciences at GUMC.

"This is the first time we have been able to identify three discrete brain areas that help people recognize and understand the sounds they are hearing," says Rauschecker. "These sounds, such as speech, are vitally important to humans, and it is critical that we understand how they are processed in the human brain."
Rauschecker and his colleagues at Georgetown have been instrumental in building a unified theory about how the human brain processes speech and language. They have shown that both human and non-human primates process speech along two parallel pathways, each of which run from lower to higher functioning neural regions.

These pathways are dubbed the "what" and "where" streams and are roughly analogous to how the brain processes sight, but in different regions. The "where" stream localizes sound and the "what" pathway identifies the sound.
Both pathways begin with the processing of signals in the auditory cortex, located inside a deep fissure on the side of the brain underneath the temples - the so-called "temporal lobe." Information processed by the "what" pathway then flows forward along the outside of the temporal lobe, and the job of that pathway is to recognize complex auditory signals, which include communication sounds and their meaning (semantics). The "where" pathway is mostly in the parietal lobe, above the temporal lobe, and it processes spatial aspects of a sound — its location and its motion in space — but is also involved in providing feedback during the act of speaking.

Auditory perception - the processing and interpretation of sound information - is tied to anatomical structures; signals move from lower to higher brain regions, Rauschecker says. "Sound as a whole enters the ear canal and is first broken down into single tone frequencies, then higher-up neurons respond only to more complex sounds, including those used in the recognition of speech, as the neural representation of the sound moves through the various brain regions," he says.

In this study, Rauschecker and his colleagues — computational neuroscientist Maximilian Riesenhuber, Ph.D., and Mark Chevillet, a student in the Interdisciplinary Program in Neuroscience — identified the three distinct areas in the "what" pathway in humans that had been seen in non-human primates. Only two had been recognized before in previous human studies.

The first, and most primary, is the "core" which analyzes tones at the basic level of simple frequencies. The second area, the "belt", wraps around the core, and integrates several tones, "like buzz sounds," that lie close to each other, Rauschecker says. The third area, the "parabelt," responds to speech sounds such as vowels, which are essentially complex bursts of multiple frequencies.

Rauschecker is fascinated by the fact that although speech and language are considered to be uniquely human abilities, the emerging picture of brain processing of language suggests "in evolution, language must have emerged from neural mechanisms at least partially available in animals," he says. "There appears to be a conservation of certain processing pathways through evolution in humans and nonhuman primates."

Source EurekaAlert!

City living affects your brain, researchers find

The part of the brain that senses danger becomes overactive in city-dwellers when they are under stress.

The brains of people living in cities operate differently from those in rural areas, according to a brain-scanning study. Scientists found that two regions, involved in the regulation of emotion and anxiety, become overactive in city-dwellers when they are stressed and argue that the differences could account for the increased rates of mental health problems seen in urban areas.

Previous research has shown that people living in cities have a 21% increased risk of anxiety disorders and a 39% increased risk of mood disorders. In addition, the incidence of schizophrenia is twice as high in those born and brought up in cities.
In the new study, Professor Andreas Meyer-Lindenberg of the University of Heidelberg in Germany scanned the brains of more than 50 healthy volunteers, who lived in a range of locations from rural areas to large cities, while they were engaged in difficult mental arithmetic tasks. The experiments were designed to make the groups of volunteers feel anxious about their performance.

The results, published in Nature, showed that the amygdala of participants who currently live in cities was over-active during stressful situations. "We know what the amygdala does; it's the danger-sensor of the brain and is therefore linked to anxiety and depression," said Meyer-Lindenberg.
Another region called the cingulate cortex was overactive in participants who were born in cities. "We know [the cingulate cortex] is important for controlling emotion and dealing with environmental adversity."

This excess activity could be at the root of the observed mental health problems, said Meyer-Lindenberg. "We speculate that stress might cause these abnormalities in the first place – that speculation lies outside what we can show in our study, it is primarily based on the fact that this specific brain area is very sensitive to developmental stress. If you stress an animal, you will find even structural abnormalities in that area and those may be enduring and make an animal anxious. What we're proposing is that stress causes these things and stress is where they are expressed and then lead to an increased risk of mental illness."

By 2050, almost 70% of people are predicted to be living in urban areas. On average, city dwellers are "wealthier and receive improved sanitation, nutrition, contraception and healthcare", wrote the researchers in Nature. But urban living is also associated with "increased risk for chronic disorders, a more demanding and stressful social environment and greater social disparities. The biological components of this complex landscape of risk and protective factors remain largely uncharacterised."

In an accompanying commentary in Nature, Dr Daniel Kennedy and Prof Ralph Adolphs, both at the California Institute of Technology, said that there are wide variations in a people's preferences for, and ability to cope with, city life.
"Some thrive in New York city; others would happily swap it for a desert island. Psychologists have found that a substantial factor accounting for this variability is the perceived degree of control that people have over their daily lives. Social threat, lack of control and subordination are all likely candidates for mediating the stressful effects of city life, and probably account for much of the individual differences."

Working out what factors in a city cause the stress in the first place is the next step in trying to understand the mental health effects of urban areas. Meyer-Lindenberg said that social fragmentation, noise or over-crowding might all be factors. "There's prior evidence that if someone invades your personal space, comes too close to you, it's exactly that amygdala-cingulate circuit that gets [switched on] so it could be something as simple as density."

He said the research could be used, in future, to inform city design.
"What we can do is try and make cities better places to live in from the view of mental health. Up to now, there really isn't a lot of evidence-base to tell a city planner what would be good, what would be bad."

Source The Guardian 

Breeding with Neanderthals helped humans go global

WHEN the first modern humans left Africa they were ill-equipped to cope with unfamiliar diseases. But by interbreeding with the local hominins, it seems they picked up genes that protected them and helped them eventually spread across the planet.

The publication of the Neanderthal genome last year offered proof that Homo sapiens bred with Neanderthals after leaving Africa. There is also evidence that suggests they enjoyed intimate relations with other hominins including the Denisovans, a species identified last year from a Siberian fossil.

But what wasn't known is whether the interbreeding made any difference to their evolution. To find out Peter Parham of Stanford University in California took a closer look at the genes they picked up along the way.

He focused on human leukocyte antigens (HLAs), a family of about 200 genes that is essential to our immune system. It also contains some of the most variable human genes: hundreds of versions - or alleles - exist of each gene in the population, allowing our bodies to react to a huge number of disease-causing agents and adapt to new ones.

The humans that left Africa probably carried only a limited number of HLA alleles as they likely travelled in small groups. Worse, their HLAs would have been adapted to African diseases.

When Parham compared the HLA genes of people from different regions of the world with the Neanderthal and Denisovan HLAs, he found evidence that non-African humans picked up new alleles from the hominins they interbred with.

One allele, HLA-C*0702, is common in modern Europeans and Asians but never seen in Africans; Parham found it in the Neanderthal genome, suggesting it made its way into H. sapiens of non-African descent through interbreeding. HLA-A*11 had a similar story: it is mostly found in Asians and never in Africans, and Parham found it in the Denisovan genome, again suggesting its source was interbreeding outside of Africa.

Parham points out that because Neanderthals and Denisovans had lived outside Africa for over 200,000 years by the time they encountered H. sapiens, their HLAs would have been well suited to local diseases, helping to protect migrating H. sapiens too.

While only 6 per cent of the non-African modern human genome comes from other hominins, the share of HLAs acquired during interbreeding is much higher. Half of European HLA-A alleles come from other hominins, says Parham, and that figure rises to 72 per cent for people in China, and over 90 per cent for those in Papua New Guinea.

This suggests they were increasingly selected for as H. sapiens moved east. That could be because humans migrating north would have faced fewer diseases than those heading towards the tropics of south-east Asia, says Chris Stringer of the Natural History Museum in London.

Parham presented his work at a Royal Society discussion meeting on human evolution in London last week.

 Source New Scientist

Teens look to parents more than friends for sexual role models

Recent adolescent sexual health study shatters stereotypes

This release is available in French. MONTREAL, June 15, 2011 – The results of a national online study show that 45% consider their parents to be their sexuality role model. Shattering stereotypes that parents and society hold about teen sexuality, the survey also revealed that only 32% looked to their friends and just 15% took inspiration from celebrities. Dr. Jean-Yves Frappier, a researcher at the University of Montreal's affiliated CHU Sainte-Justine Hospital Research Centre will be presenting the results at the Canadian Paediatric Society's 88th Annual Conference on June 18, 2011.

Importantly, the survey also revealed that many of the teenagers who look to their parents live in families where sexuality is openly discussed, and that moreover, teenagers in these families have a greater awareness of the risks and consequences of sexually transmitted infections. "Good communication within families and especially around sexual health issues is associated with more responsible behaviours," Frappier said.
However, 78% of the mothers who participated in the survey believed that their children modeled their friends' sexual behaviour, and that a lack of involvement of communication with fathers is especially detrimental. "Parents seem to underestimate their role and the impact that they have," Frappier noted. "Health professionals and the media have an important role to play in empowering parents and enabling them to increase their communications with their children with regards to sexual health issues."

The survey involved 1139 mothers of teenagers and 1171 youths between 14 and 17 years of age. The questionnaire touched on topics such as sources of sexual health information, communication about sexual health, family functioning and sexual activities. This study was financed in part by a grant from Merck Frosst Co. The University of Montreal is known officially as Université de Montréal. The Research Centre of the CHU Sainte-Justine is known officially as the Centre de recherche du Centre hospitalier universitaire Sainte-Justine.

Source  EurekaAlert!

It is human nature to cooperate with strangers

It seems humans really are the cooperative ape. A nomadic society in east Africa that lacks a centralised government can still regularly muster armies of several hundred warriors, most of whom are strangers to each other.

We are the only species prepared to cooperate in large numbers with unrelated individuals. The feeling was that such behaviour was a recent development, requiring a centralised political authority. Now it seems possible that such cooperation could have predated these organisational structures and may have featured in numerous large prehistoric societies hundreds of thousands of years ago.

Sarah Mathew and Robert Boyd of the University of California in Los Angeles interviewed 118 Turkana men. An ethnic group from east Africa, the Turkana live in small households that regularly move around to find fresh pasture for their animals. If a small group of Turkana men want to seize livestock from other ethnic groups they can rally a raiding party of several hundred men through word of mouth.

The interviews revealed that these raids are risky – on a given raid each man has a 1.1 per cent chance of being killed – and some men are reluctant to participate. On 43 per cent of raids, at least one man deserted before combat, and in 45 per cent of battles someone behaved in a cowardly fashion. Such "cheats" are informally judged by the community, and may be tied to a tree and beaten. Mathew and Boyd speculate that this punishment helps drive cooperation in the absence of centralised government.

Samuel Bowles of the Santa Fe Institute in New Mexico agrees that punishment may have spurred the development of large-scale cooperation. He says this cooperation may have set modern humans on the path to success.

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1105604108

Source New Scientist