Neuroscience

Linguistics and biology researchers propose a new theory on the deep roots of human speech.

“The sounds uttered by birds offer in several respects the nearest analogy to language,” Charles Darwin wrote in “The Descent of Man” (1871), while contemplating how humans learned to speak. Language, he speculated, might have had its origins in singing, which “might have given rise to words expressive of various complex emotions.”

Now researchers from MIT, along with a scholar from the University of Tokyo, say that Darwin was on the right path. The balance of evidence, they believe, suggests that human language is a grafting of two communication forms found elsewhere in the animal kingdom: first, the elaborate songs of birds, and second, the more utilitarian, information-bearing types of expression seen in a diversity of other animals.

“It’s this adventitious combination that triggered human language,” says Shigeru Miyagawa, a professor of linguistics in MIT’s Department of Linguistics and Philosophy, and co-author of a new paper published in the journal Frontiers in Psychology.

The idea builds upon Miyagawa’s conclusion, detailed in his previous work, that there are two “layers” in all human languages: an “expression” layer, which involves the changeable organization of sentences, and a “lexical” layer, which relates to the core content of a sentence. His conclusion is based on earlier work by linguists including Noam Chomsky, Kenneth Hale and Samuel Jay Keyser.

Based on an analysis of animal communication, and using Miyagawa’s framework, the authors say that birdsong closely resembles the expression layer of human sentences — whereas the communicative waggles of bees, or the short, audible messages of primates, are more like the lexical layer. At some point, between 50,000 and 80,000 years ago, humans may have merged these two types of expression into a uniquely sophisticated form of language.

“There were these two pre-existing systems,” Miyagawa says, “like apples and oranges that just happened to be put together.”

These kinds of adaptations of existing structures are common in natural history, notes Robert Berwick, a co-author of the paper, who is a professor of computational linguistics in MIT’s Laboratory for Information and Decision Systems, in the Department of Electrical Engineering and Computer Science.

“When something new evolves, it is often built out of old parts,” Berwick says. “We see this over and over again in evolution. Old structures can change just a little bit, and acquire radically new functions.”

A new chapter in the songbook

The new paper, “The Emergence of Hierarchical Structure in Human Language,” was co-written by Miyagawa, Berwick and Kazuo Okanoya, a biopsychologist at the University of Tokyo who is an expert on animal communication.

To consider the difference between the expression layer and the lexical layer, take a simple sentence: “Todd saw a condor.” We can easily create variations of this, such as, “When did Todd see a condor?” This rearranging of elements takes place in the expression layer and allows us to add complexity and ask questions. But the lexical layer remains the same, since it involves the same core elements: the subject, “Todd,” the verb, “to see,” and the object, “condor.”

Birdsong lacks a lexical structure. Instead, birds sing learned melodies with what Berwick calls a “holistic” structure; the entire song has one meaning, whether about mating, territory or other things. The Bengalese finch, as the authors note, can loop back to parts of previous melodies, allowing for greater variation and communication of more things; a nightingale may be able to recite from 100 to 200 different melodies.

By contrast, other types of animals have bare-bones modes of expression without the same melodic capacity. Bees communicate visually, using precise waggles to indicate sources of foods to their peers; other primates can make a range of sounds, comprising warnings about predators and other messages.

Humans, according to Miyagawa, Berwick and Okanoya, fruitfully combined these systems. We can communicate essential information, like bees or primates — but like birds, we also have a melodic capacity and an ability to recombine parts of our uttered language. For this reason, our finite vocabularies can generate a seemingly infinite string of words. Indeed, the researchers suggest that humans first had the ability to sing, as Darwin conjectured, and then managed to integrate specific lexical elements into those songs.

“It’s not a very long step to say that what got joined together was the ability to construct these complex patterns, like a song, but with words,” Berwick says.

As they note in the paper, some of the “striking parallels” between language acquisition in birds and humans include the phase of life when each is best at picking up languages, and the part of the brain used for language. Another similarity, Berwick notes, relates to an insight of celebrated MIT professor emeritus of linguistics Morris Halle, who, as Berwick puts it, observed that “all human languages have a finite number of stress patterns, a certain number of beat patterns. Well, in birdsong, there is also this limited number of beat patterns.”

Birds and bees

Norbert Hornstein, a professor of linguistics at the University of Maryland, says the paper has been “very well received” among linguists, and “perhaps will be the standard go-to paper for language-birdsong comparison for the next five years.”

Hornstein adds that he would like to see further comparison of birdsong and sound production in human language, as well as more neuroscientific research, pertaining to both birds and humans, to see how brains are structured for making sounds.

The researchers acknowledge that further empirical studies on the subject would be desirable.

“It’s just a hypothesis,” Berwick says. “But it’s a way to make explicit what Darwin was talking about very vaguely, because we know more about language now.”

Miyagawa, for his part, asserts it is a viable idea in part because it could be subject to more scrutiny, as the communication patterns of other species are examined in further detail. “If this is right, then human language has a precursor in nature, in evolution, that we can actually test today,” he says, adding that bees, birds and other primates could all be sources of further research insight.

MIT-based research in linguistics has largely been characterized by the search for universal aspects of all human languages. With this paper, Miyagawa, Berwick and Okanoya hope to spur others to think of the universality of language in evolutionary terms. It is not just a random cultural construct, they say, but based in part on capacities humans share with other species. At the same time, Miyagawa notes, human language is unique, in that two independent systems in nature merged, in our species, to allow us to generate unbounded linguistic possibilities, albeit within a constrained system.

“Human language is not just freeform, but it is rule-based,” Miyagawa says. “If we are right, human language has a very heavy constraint on what it can and cannot do, based on its antecedents in nature.”

Hypnosis has begun to attract renewed interest from neuroscientists interested in using hypnotic suggestion to test predictions about normal cognitive functioning.

To demonstrate the future potential of this growing field, guest editors Professor Peter Halligan from the School of Psychology at Cardiff University and David A. Oakley of University College London, brought together leading researchers from cognitive neuroscience and hypnosis to contribute to this month’s special issue of the international journal, Cortex.

The issue illustrates how methodological and theoretical advances, using hypnotic suggestion, can return novel and experimentally verifiable insights for the neuroscience of consciousness and motor control. The research also includes novel brain imaging studies, which address sceptics’ concerns regarding the subjective reality and comparability of hypnotically suggested phenomena that previously depended on subjects’ largely unverifiable report and behaviour.

Halligan and Oakley also contribute to a new and revealing brain imaging study in the special issue that explores the brain systems involved in hypnotic paralysis. This research follows their earlier pioneering work on hypnotic leg paralysis reported in the Lancet in 2000.

Patients with “functional” or “psychogenic” conversion disorders present symptoms, such as paralyses, are clinically challenging. They comprise between 30 and 40% of patients attending neurology outpatient clinics and place a huge strain on public health services.

Professor Halligan of Cardiff University’s School of Psychology said: “This new study, working with colleagues at the Institute of Psychiatry in London, suggests that hypnosis can provide insights into of the brain systems involved in patients who display symptoms of neurological illness, but without evidence of brain damage. New insights show that symptoms experienced by patients with functional or dissociative conversion disorders (e.g. medically unexplained paralysis) can be simulated using targeted hypnotic suggestion.

"In this study we monitored brain activations of healthy volunteers with hypnosis induction who experienced paralysis-like experiences which could be turned ‘on’ and ‘off’. The suggestion resulted in subjects being unable to move a joystick together with a realistic and compelling experience of being unable to move and control their left hand despite trying.

"When compared to the completed movements, the suggested paralysis condition revealed increased activity in brain regions know to be active during motor planning and intention to move – and also brain areas involved in response selection and inhibition."

Comparing symptoms conveyed by conversion disorder patients and those produced by ‘paralysis’ suggestions in hypnosis, has revealed similar patterns of brain activation associated with attempted movement of the affected limb.

These findings could inform future studies of the brain mechanisms underpinning limb paralysis in patients with conversion disorders. More importantly they could lead to effective treatments.

Electrodes operated into the brain are today used in research and to treat diseases such as Parkinson’s. However, their use has been limited by their size. At Lund University in Sweden, researchers have, for the first time, succeeded in implanting an ultrathin nanowire-based electrode and capturing signals from the nerve cells in the brain of a laboratory animal.

The researchers work at Lund University’s Neuronano Research Centre in an interdisciplinary collaboration between experts in subjects including neurophysiology, biomaterials, electrical measurements and nanotechnology. Their electrode is composed of a group of nanowires, each of which measures only 200 nanometres (billionths of a metre) in diameter.

Such thin electrodes have previously only been used in experiments with cell cultures.

“Carrying out experiments on a living animal is much more difficult. We are pleased that we have succeeded in developing a functioning nano-electrode, getting it into place and capturing signals from nerve cells”, says Professor Jens Schouenborg, who is head of the Neuronano Research Centre.

He sees this as a real breakthrough, but also as only a step on the way. The research group has already worked for several years to develop electrodes that are thin and flexible enough not to disturb the brain tissue, and with material that does not irritate the cells nearby. They now have the first evidence that it is possible to obtain useful nerve signals from nanometre-sized electrodes.

The research will now take a number of directions. The researchers want to try and reduce the size of the base to which the nanowires are attached, improve the connection between the electrode and the electronics that receive the signals from the nerve cells, and experiment with the surface structure of the electrodes to see what produces the best signals without damaging the brain cells.

“In the future, we hope to be able to make electrodes with nanostructured surfaces that are adapted to the various parts of the nerve cells – parts that are no bigger than a few billionths of a metre. Then we could tailor-make each electrode based on where it is going to be placed and what signals it is to capture or emit”, says Jens Schouenborg.

When an electrode is inserted into the brain of a patient or a laboratory animal, it is generally anchored to the skull. This means that it doesn’t move smoothly with the brain, which floats inside the skull, but rather rubs against the surrounding tissue, which in the long term causes the signals to deteriorate. The Lund group’s electrodes will instead be anchored by their surface structure.

“With the right pattern on the surface, they will stay in place yet still move with the body – and the brain – thereby opening up for long-term monitoring of neurones”, explains Jens Schouenborg.

He praises the collaboration between medics, physicists and others at the Neuronano Research Centre, and mentions physicist Dmitry B. Suyatin in particular. He is the principal author of the article which the researchers have now published in the international journal PLOS ONE.

The overall goal of the Neuronano Research Centre is to develop electrodes that can be inserted into the brain to study learning, pain and other mechanisms, and, in the long term, to treat conditions such as chronic pain, depression and Parkinson’s disease.

Study finds fog-like condition related to chemotherapy’s effect on new brain cells and rhythms.

It’s not unusual for cancer patients being treated with chemotherapy to complain about not being able to think clearly, connect thoughts or concentrate on daily tasks. The complaint – often referred to as chemo-brain – is common. The scientific cause, however, has been difficult to pinpoint.

New research by Rutgers University behavioral neuroscientist Tracey Shors offers new clues for this fog-like condition, medically known as chemotherapy-induced cognitive impairment. In a featured article published in the European Journal of Neuroscience, Shors and her colleagues argue that prolonged chemotherapy decreases the development of new brain cells, a process known as neurogenesis, and disrupts ongoing brain rhythms in the part of the brain responsible for making new memories. Both, she says, are affected by learning and in some cases are necessary for learning to occur.

“One of the things that these brain rhythms do is to connect information across brain regions,” says Shors, Professor II in the Department of Psychology and Center for Collaborative Neuroscience at Rutgers. “We are starting to have a better understanding of how these natural rhythms are used in the process of communication and how they change with experience.”

Working in the Shors laboratory, postdoctoral fellow Miriam S. Nokia from the Department of Psychology at the University of Jyvaskyla in Finland and Rutgers neuroscience graduate student Megan Anderson treated rats with a chemotherapy drug – temozolomide (TMZ) – used on individuals with either malignant brain tumors or skin cancer to stop rapidly dividing cells that have gone out of control and resulted in cancer.

In this study, scientists found that the production of new healthy brain cells treated with the TMZ was reduced in the hippocampus by 34 percent after being caught in the crossfire of the drug’s potency. The cell loss, coupled with the interference in brain rhythms, resulted in the animal being unable to learn difficult tasks.

Shors says the rats had great difficulty learning to associate stimulus events if there was a time gap between the activities but could learn simple task if the stimuli were not separated in time.  Interestingly, she says, the drug did not disrupt the memories that were already present when the treatment began.

For cancer patients undergoing long-term chemotherapy this could mean that although they are able to do simple everyday tasks, they find it difficult to do more complicated activities like processing long strings of numbers, remembering recent conversations, following instructions and setting priorities. Studies indicate that while most cancer patients experience short-term memory loss and disordered thinking, about 15 percent of cancer patients suffer more long-lasting cognitive problems as a result of the chemotherapy treatment.

“Chemotherapy is an especially difficult time as patients are learning how to manage their treatment options while still engaging in and appreciating life. The disruptions in brain rhythms and neurogenesis during treatment may explain some of the cognitive problems that can occur during this time. The good news is that these effects are probably not long-lasting,” says Shors.

A University of Illinois study has established a possible link between high-fat diets and such childhood brain-based conditions as attention deficit hyperactivity disorder (ADHD) and memory-dependent learning disabilities.

“We found that a high-fat diet rapidly affected dopamine metabolism in the brains of juvenile mice, triggering anxious behaviors and learning deficiencies. Interestingly, when methylphenidate (Ritalin) was administered, the learning and memory problems went away,” said Gregory Freund, a professor in the U of I College of Medicine and a member of the university’s Division of Nutritional Sciences.

The research was published in Psychoneuroendocrinology.

Freund said that altered dopamine signaling in the brain is common to both ADHD and the overweight or obese state. “And an increase in the number of dopamine metabolites is associated with anxiety behaviors in children,” he added.

Intrigued by the recent upsurge in both child obesity and adverse childhood psychological conditions, including impulsivity, depression, and ADHD, Freund’s team examined the short-term effects of a high-fat (60% calories from fat) versus a low-fat (10% calories from fat) diet on the behavior of two groups of four-week-old mice. A typical Western diet contains from 35 to 45 percent fat, he said.

“After only one week of the high-fat diet, even before we were able to see any weight gain, the behavior of the mice in the first group began to change,” he said.

Evidence of anxiety included increased burrowing and wheel running as well a reluctance to explore open spaces. The mice also developed learning and memory deficits, including decreased ability to negotiate a maze and impaired object recognition.

Switching mice from a high-fat to a low-fat diet restored memory in one week, he noted.

In mice that continued on the high-fat diet, impaired object recognition remained three weeks after the onset of symptoms. But Freund knows from other studies that brain biochemistry normalizes after 10 weeks as the body appears to compensate for the diet. At that point, brain dopamine has returned to normal, and mice have become obese and developed diabetes.

“Although the mice grow out of these anxious behaviors and learning deficiencies, the study suggests to me that a high-fat diet could trigger anxiety and memory disorders in a child who is genetically or environmentally susceptible to them,” he said.

Because the animals adapt to the high-fat fare, the scientists also hypothesized that abruptly removing fat from the diet might negatively affect anxiety, learning, and memory.

The researchers had expected that the high-fat diet would stimulate inflammation, which is associated with obesity, but they saw no evidence of an inflammatory response in the brain after one or three weeks on the high-fat regimen.

Instead, they saw evidence that a high-fat diet initiates chemical responses that are similar to the ones seen in addiction, with dopamine, the chemical important to the addict’s pleasurable experiences, increasing in the brain.

Supposedly ‘primitive’ reflexes may involve more sophisticated brain function than previously thought, according to researchers at Imperial College London.

The vestibular-ocular reflex (or VOR), common to most vertebrates, is what allows us to keep our eyes focused on a fixed point even while our heads are moving. Up until now, scientists had assumed this reflex was controlled by the lower brainstem, which regulates eating, sleeping and other low-level tasks.

Researchers at Imperial’s Division of Brain Sciences conducted tests to examine this reflex in left- and right-handed subjects, revealing that handedness plays a key role in the way it operates. This suggests that higher-level functions in the cortex, which govern handedness, are involved in the control of primitive reflexes such as the VOR.

The research, published in the Journal of Neuroscience, involved seating volunteers in a motorised chair which was then spun around at a speed of one revolution every four seconds. This allowed the experimenters to study the VOR by measuring the time it took for the eyes to adjust to the spinning motion. The subjects were then presented with what are known as bistable visual phenomena, optical illusions which appear to flip between two images. Famous examples include the duck which resembles a rabbit, and the cube outline which appears to come out of and go into the page simultaneously.

Scientists already know that this bistable perception is controlled by a part of the cortex which governs more complex, decision-based tasks. Because of this, researcher Qadeer Arshad and his colleagues did not expect to find any link between the two processes.

They were surprised to find that processing bistable phenomena disrupted people’s ability to stabilise their gaze, following rightward rotation in right handers and leftward rotation in left handers. Arshad said “This is the first time that anything of this kind has been shown. Up until now, the vestibular-ocular reflex was considered a low-level reflex, not even approaching higher-order brain function. Now it seems that this primitive reflex was specialised into the cortex, the part of the brain which governs our sense of direction.”

This study could help scientists understand why some people become dizzy through experiencing purely visual stimuli, such as flickering lights or busy supermarket aisles. Professor Adolfo Bronstein, a co-author on the paper, said “Most causes of dizziness start with an inner ear - or vestibular - disorder but this initial phase tends to settle quite rapidly.  In some patients, however, dizziness becomes a problematic long term problem and their dizziness becomes visually induced. The experimental set-up we used would be ideally suited to help us understand how visual stimuli could lead to long-term dizziness. In fact, we have already carried out research at Imperial around using complex visual stimuli to treat patients with long-term dizziness”