Posts tagged Broca's area
Articles and news from the latest research reports.
Our Brains are Hardwired for Language
People blog, they don’t lbog, and they schmooze, not mshooze. But why is this? Why are human languages so constrained? Can such restrictions unveil the basis of the uniquely human capacity for language?
A groundbreaking study published in PLOS ONE by Prof. Iris Berent of Northeastern University and researchers at Harvard Medical School shows the brains of individual speakers are sensitive to language universals. Syllables that are frequent across languages are recognized more readily than infrequent syllables. Simply put, this study shows that language universals are hardwired in the human brain.
LANGUAGE UNIVERSALS
Language universals have been the subject of intense research, but their basis remains elusive. Indeed, the similarities between human languages could result from a host of reasons that are tangential to the language system itself. Syllables like lbog, for instance, might be rare due to sheer historical forces, or because they are just harder to hear and articulate. A more interesting possibility, however, is that these facts could stem from the biology of the language system. Could the unpopularity of lbogs result from universal linguistic principles that are active in every human brain?
THE EXPERIMENT
To address this question, Dr. Berent and her colleagues examined the response of human brains to distinct syllable types—either ones that are frequent across languages (e.g., blif, bnif), or infrequent (e.g., bdif, lbif). In the experiment, participants heard one auditory stimulus at a time (e.g., lbif), and were then asked to determine whether the stimulus includes one syllable or two while their brain was simultaneously imaged.
Results showed the syllables that were infrequent and ill-formed, as determined by their linguistic structure, were harder for people to process. Remarkably, a similar pattern emerged in participants’ brain responses: worse-formed syllables (e.g., lbif) exerted different demands on the brain than syllables that are well-formed (e.g., blif).
UNIVERSALLY HARDWIRED BRAINS
The localization of these patterns in the brain further sheds light on their origin. If the difficulty in processing syllables like lbif were solely due to unfamiliarity, failure in their acoustic processing, and articulation, then such syllables are expected to only exact cost on regions of the brain associated with memory for familiar words, audition, and motor control. In contrast, if the dislike of lbif reflects its linguistic structure, then the syllable hierarchy is expected to engage traditional language areas in the brain.
While syllables like lbif did, in fact, tax auditory brain areas, they exerted no measurable costs with respect to either articulation or lexical processing. Instead, it was Broca’s area—a primary language center of the brain—that was sensitive to the syllable hierarchy.
These results show for the first time that the brains of individual speakers are sensitive to language universals: the brain responds differently to syllables that are frequent across languages (e.g., bnif) relative to syllables that are infrequent (e.g., lbif). This is a remarkable finding given that participants (English speakers) have never encountered most of those syllables before, and it shows that language universals are encoded in human brains.
The fact that the brain activity engaged Broca’s area—a traditional language area—suggests that this brain response might be due to a linguistic principle. This result opens up the possibility that human brains share common linguistic restrictions on the sound pattern of language.
FURTHER EVIDENCE
This proposal is further supported by a second study that recently appeared in the Proceedings of the National Academy of Science, also co-authored by Dr. Berent. This study shows that, like their adult counterparts, newborns are sensitive to the universal syllable hierarchy.
The findings from newborns are particularly striking because they have little to no experience with any such syllable. Together, these results demonstrate that the sound patterns of human language reflect shared linguistic constraints that are hardwired in the human brain already at birth.
With right-handed people, it is positioned in the left side of the brain; left-handed people have it (usually) in the right side: the location of speech production has been known for quite some time. But it is not that simple, states psychologist Gesa Hartwigsen, Professor at Kiel University. In her current scientific publication, published in the magazine Proceedings of the National Academy of Science of the USA (PNAS), she investigates which areas in the brain really are in charge of speech, and how these interact. Her findings are supposed to help patients who have speech production problems or aphasia following a stroke.
Comprehending & Speaking
Gesa Hartwigsen and her team started by analysing speech production. They let healthy right-handed test persons listen to words, which they should then repeat. “These were pseudo words such as `beudo`. In German, they don’t have any associated meaning. Therefore, when hearing and repeating these words, no areas of the brain that had a connection to the meaning of what had been heard were activated”, said Hartwigsen.
The psychologist applies a combination of non-invasive methods (fMRI– functional magnetic resonance imaging and TMS – transcranial magnetic stimulation) to deduce what happens in the brain during the test. “We thus proved that the left hemisphere, as expected, was activated during speech production, while the right hemisphere did not actively contribute to language function”, explains Hartwigsen. This is the regular functionality within a healthy brain. From these results as well as others, scientists had up to now deduced that the right hemisphere did not contribute to speech production in the healthy system and was therefore suppressed.
Interfering & Measuring
With a second test, the Kiel University scientists simulated a dysfunction in the brain comparable to a stroke. A magnetic coil transmits a current pulse that interrupts the function of the area responsible for producing speech (Broca’s Area) in the left hemisphere. This completely harmless method influences the speech production of the volunteers for about 30 to 45 minutes. “During this period, the ability to listen and repeat was tested again. While we observed a suppressed activity in the left hemisphere during repeating, with some test persons taking longer to repeat the pseudo words, we also found unexpected activities in the right hemisphere”, reports Hartwigsen.
The right hemisphere showed increased activity during pseudo word repetition. The more the activity in the right Borca’s Area increased, the faster the volunteers were able to solve their speech tests. The right hemisphere also increased its facilitatory influence on the right hemisphere, a finding that was not observed prior to the TMS-induced lesion. “This reaction lends further support to the notion that the right hemisphere area reacts to the dysfunction of the left hemisphere and tries to compensate for the lesion.” Does the right hemisphere have a supporting influence and does it play an active role in speech production? So far, the common opinion was that it does not.
Result & Outlook
The findings of Gesa Hartwigsen and her team show an interaction of both hemispheres during speech repetition. When the left hemisphere is suppressed for example by a stroke, the right hemisphere could actively facilitate speech production. “By stimulating the right hemisphere, it could be possible to support speech recovery”, speculates the scientist. Here, timing would be very important. “Right after a stroke, we could support the right hemisphere. But when the remaining areas of the left hemisphere are ready to do their work again, it might be more helpful if the right hemisphere was suppressed. During this phase, we could stimulate the left hemisphere instead. The correct timing can therefore be crucial for recovery of speech after a stroke.”
In collaboration with the Department of Neurology at Kiel University, a stroke specialist from Leipzig and doctoral students of Medicine and Psychology, Gesa Hartwigsen has started a follow-up study on the recent publication. “We would like to find out more about the collaboration of the hemispheres and the right timing in helping stroke patients to recover”, says Hartwigsen. Her field of research is fairly new within the cognitive neuroscience. Nevertheless, she is positive that it will offer practical help in the form of concrete therapies within the next ten to fifteen years.
Shout now! ‒ How Nerve Cells Initiate Voluntary Calls
University of Tübingen neuroscientists show that monkeys can decide to call out or keep silent
“Should I say something or not?” Human beings are not alone in pondering this dilemma – animals also face decisions when they communicate by voice. University of Tübingen neurobiologists Dr. Steffen Hage and Professor Andreas Nieder have now demonstrated that nerve cells in the brain signal the targeted initiation of calls – forming the basis of voluntary vocal expression. Their results are published in “Nature Communications.”
When we speak, we use the sounds we make for a specific purpose – we intentionally say what we think, or consciously withhold information. Animals, however, usually make sounds according to what they feel at that moment. Even our closest relations among the primates make sounds as a reflex based on their mood. Now, Tübingen neuroscientists have shown that rhesus monkeys are able to call (or be silent) on command. They can instrumentalize the sounds they make in a targeted way, an important behavioral ability which we also use to put language to a purpose.
To find out how the neural cells in the brain catalyse the production of controled vocal noises, the researchers taught rhesus monkeys to call out quickly when a spot appeared on a computer screen. While the monkeys solved puzzles, measurements taken in their prefrontal cortex revealed astonishing reactions in the cells there. The nerve cells became active whenever the monkey saw the spot of light which was the instruction to call out. But if the monkey simply called out spontaneously, these nerve cells were not activated. The cells therefore did not signaled for just any vocalisation – only for calls that the monkey actively decided to make.
The results published in “Nature Communications” provide valuable insights into the neurobiological foundations of vocalization. “We want to understand the physiological mechanisms in the brain which lead to the voluntary production of calls,” says Dr. Steffen Hage of the Institute for Neurobiology, “because it played a key role in the evolution of human ability to use speech.” The study offers important indicators of the function of part of the brain which in humans has developed into one of the central locations for controlling speech. “Disorders in this part of the human brain lead to severe speech disorders or even complete loss of speech in the patient,” Professor Andreas Nieder explains. The results – giving insights into how the production of sound is initiated – may help us better understand speech disorders.
(Source: uni-tuebingen.de)
In the 19th century, a speechless patient wasted away in the Bicetre Hospital in France for 21 years. He was known as ‘Tan’ for the only word he could say, and for 150 years, his identity has remained a mystery. In 1861, as Tan lay dying, the famous physician Paul Broca encountered the patient. When the ill-fated patient died, Broca autopsied his brain. Broca noticed a lesion in a part of the brain tucked up behind the eyes. He concluded that the brain region was responsible for language processing. But despite Tan becoming one of the most famous medical patients in history, he was never identified until now.
A 2007 study in the journal Brain revealed the extent of the lesion using MRI imaging. A recent study identified the patient as a Monsieur Louis Leborgne, a craftsman who had suffered from epilepsy his whole life.
Neuroscientists find Broca’s area is really two subunits, each with its own function
A century and a half ago, French physician Pierre Paul Broca found that patients with damage to part of the brain’s frontal lobe were unable to speak more than a few words. Later dubbed Broca’s area, this region is believed to be critical for speech production and some aspects of language comprehension.
However, in recent years neuroscientists have observed activity in Broca’s area when people perform cognitive tasks that have nothing to do with language, such as solving math problems or holding information in working memory. Those findings have stimulated debate over whether Broca’s area is specific to language or plays a more general role in cognition.
A new study from MIT may help resolve this longstanding question. The researchers, led by Nancy Kanwisher, the Walter A. Rosenblith Professor of Cognitive Neuroscience, found that Broca’s area actually consists of two distinct subunits. One of these focuses selectively on language processing, while the other is part of a brainwide network that appears to act as a central processing unit for general cognitive functions.
"I think we’ve shown pretty convincingly that there are two distinct bits that we should not be treating as a single region, and perhaps we shouldn’t even be talking about ‘Broca’s area’ because it’s not a functional unit," says Evelina Fedorenko, a research scientist in Kanwisher’s lab and lead author of the new study, which recently appeared in the journal Current Biology.