Speech Listening Excites Tongue Muscles

The European Journal of Neuroscience published a TMS study done by L. Fadiga, L. Craighero, G. Buccino, and G. Rizzolatti, which investigated the neural mechanisms underlying speech perception. Through TMS, they demonstrated that while listening to speech, there is an increase of motor-evoked potentials recorded from the listeners’ tongue muscles when the words involve tongue movements upon pronunciation. The excitement of the listener’s motor cortex and thus tongue muscles was revealed by TMS. They also found stronger effects for words than for pseudo-words, meaning there is some motor result of recognizing an existing word (or at least one they are aware of). The activation is very specific because phonemes requiring a stronger use of the tongue muscles automatically excite motor centers controlling tongue muscles.

This is such an interesting phenomenon and seems like it could be linked to or part of the mirror neuron system. Evolutionarily, I’m not sure why this would be an important mechanism because I don’t see why it is advantageous to imitate the words of others, but perhaps on a simpler level, it helps with learning, identifying and speaking the same language. But I do think such findings will contribute to understanding speech problems and the way we perceive words and languages.

Insights on Language and the Brain Through TMS

J. T. Devlin and K. E. Watkins were published in the Oxford Journals, writing about the importance of TMS as a tool for brain research, particularly with language and speech. Though language research with TMS is still very young, they point out how clearly beneficial it is in studying both cognition and neurobiology. Findings include that susceptibility to unilateral lesions is related to pre-morbid language organization, and that left hemisphere activation is more critical for performance in aphasic people than right hemisphere activation. Also, use of TMS has demonstrated a link between action words and motor programs, as well as a possible evolutionary link between hand gestures and language. They found that speech perception signals the motor system to produce correlate movements. So applying the tools of TMS may help trace neural circuitry underlying human language processing. It seems like there is a lot of potential in this area of TMS and language and that discoveries are only accelerating. The implications of diagnosing, aiding in, or understanding development or speech problems are quite exciting.

Role of Music in Neuroscience

Robert Zatorre, in the journal Nature, surveys the importance of music in neuroscience, an area of research that is yet underdeveloped. Music allows us to study various aspects of neuroscience, including motor-skills, memory, and emotion, and processing music (listening to or making) requires a mixture of almost all cognitive functions. Certain neurological functions associated with music are unique to music, and others overlap with those in involved in other domains. For example, there is much evidence that speech processing mostly happens in the left hemisphere. And often musical function is intact even if the left hemisphere is severely damaged. Lesions and magnetic recording studies have shown that a certain region of the auditory cortex in the right hemisphere is much more specialized in pitch details than its counterpart in the left hemisphere.

Some lesions of auditory cortical regions result in a problem called amusia, which is a highly selective dysfunction in perceiving and interpreting music. Though they have no issues with speaking words or understanding/recognizing speech and everyday sounds, they cannot pick out wrong notes in music or recognize a familiar melody. The fine-grained pitch processing that is damaged in amusia and is essential and characteristic of music perception, helps in determining specifics of the brain on music and the brain on other functions.

Even in development, music is a large indicator of the plasticity of the brain. Music perception starts very early on, and babies are able to sort out and create rules for the musical sounds they hear. But obviously there are largely varying degrees of abilities and affinities for music throughout individuals. Years of training actually can change underlying structures of the nervous system, as evidenced through studies showing greater tissue density and enlargement of motor and auditory structures in musicians. The way that mechanism of music in the brain are so intricately woven but also changed contributes to the plasticity of the brain, and the importance of the environment’s effect on the brain.

Prefrontal Cortex and Empathic Response

In a study published in the MIT Press Journals, Shamay-Tsoory et al investigated empathy deficits after prefrontal damage. Patients with localized lesions in the prefrontal cortex were tested for empathic response, and they were compared to patients with posterior lesions as well as healthy control subjects. In order to study cognitive processes involved with empathy, they also looked at the relationships between empathy scores and performance on tasks that assess processes of cognitive flexibility, affect recognition, and theory of mind. They found that patients with prefrontal lesions, especially with damaged ventromedial prefrontal cortexes, had very impaired empathy abilities compared to those with posterior lesions and healthy subjects. Posterior lesion patients’ results were divided by hemisphere: if damaged in the right hemisphere they were impaired, but if damaged in the left, they were similar to healthy controls. These findings, along with other relationships between empathy and task performances, indicated that the right ventromedial cortex is important in integrating cognition that is crucial to producing empathic response. Also, more generally, they support that the prefrontal brain structures are necessary for mediating empathic responses.

Hopefully more confirmation of the importance of the ventromedial prefrontal cortex in empathy/empathic response will contribute to better diagnoses and understanding behind seemingly odd social consequences of those with this brain damage. Perhaps this will even allow researchers to tap into personality functions and disorders and how the brain plays a role in empathic behaviors.

Babies Process Words Like Grown-Ups

According to a study by Katherine E. Travis at the University of California, San Diego, babies actually process words using the same brain structures as adults, and they comprehend the meanings of many of the words they hear, or comprehend them as more than mere simple sounds. Using MEG (magnetoencephalography, a scan measuring magnetic fields emitted by neurons in the brain) and MRI (magnetic resonance imaging), Travis and others non-invasively studied brain activity in infants ranging from 12 to 18 months, and they discovered that the brain mechanisms adults use to access meanings of words- what they call a continually updated “mental database” of meanings- are the same ones that babies use.

Previously, scientists assumed that babies process words with an entirely separate learning mechanism, and that learning begins in a certain way early on and later evolves into the “adult way.” Despite lesions in Broca’s and Wernicke’s areas are known to be linked to language skills loss in adults, not much had been known or researched on such impact in childhood.

For some reason, this does not seem too surprising- that the same mechanisms are used in both early childhood and in adulthood, but that obviously the mechanism is developed and updated through time. It doesn’t seem particularly parsimonious for there to be an altogether different mechanism. Regardless, I think this research could help in predicting or diagnosing autism or language disabilities, as well as in opening doors for more discoveries with language.

No Harm By Migraines?

A recently published study in the British Medical Journal presents what may be relieving news for migraine sufferers. Research by Christophe Tzourio at the University Pierre et Marie Curie shows that even chronic and severe forms of migraines do not cause any damage to the brain. Interestingly, there has been research with MRI previously done, showing that those with chronic, full-on migraines are more likely to have tiny lesions to microvessels in the brain. The lesions occur when small cerebral arteries that supply blood to white matter deteriorate. The same types of lesions actually occur in elderly people, diabetics, and hypertensive people, and they are linked to depression, Alzheimer’s, stroke risk, and impaired memory. Tzourio tested cognitive abilities of over 800 senior citizens in France, of whom almost 15 percent had suffered migraines throughout their lives. No matter how debilitating the migraines, the senior citizens all had virtually indistinguishable scores. There was no cognitive damage detected by way of migraines. Thus, even with tiny lesions to brain microvessels, migraines seem to be “harmless.”

I would like to see further research done with this, because I am not sure that such a study provides significant enough evidence to confidently say that migraines do not cause cognitive damage or harm. Also, I wonder if this means that microvessel lesions are harmless? Obviously, it would be a great relief if these results are indeed true, but somehow it seems too sweeping a statement to conclude.

The Adolescent's Social Brain

Sarah-Jayne Blakemore’s article in Nature Reviews: Neuroscience about the social brain in adolescence highlights the undeniable social cognition and behavioral changes that accompany adolescence. She describes the way these changes occur alongside functional changes in the social brain, defined as the “network of brain regions that are involved in understanding others.” Providing mostly evidence from fMRIs, but also from EEGs and brain lesions, she concludes that particularly the medial prefrontal cortex and superior temporal sulcus are focal regions in the brain that undergo functional and structural changes throughout adolescence. Studies suggest that certain prefrontal activity increases from childhood to adolescence, then decreases from early adolescence to adulthood, which may be explained by elimination of unused synapses. In addition, adolescents seem to have higher levels of activity in the prefrontal cortex with face-processing, mentalizing tasks, and emotion-recognition than do adults.

Blakemore also points out that many questions are still unanswered, including how the environment influences brain development in adolescence and what triggers reorganization of synapses during puberty. Such questions regarding adolescent behavioral changes should not be simply studied using neurobiology, but also considering hormonal and social differences. Regardless, the adolescent social brain is a relatively unpopular topic of research, which makes this article even more intriguing. Hopefully more speculations will spur further studies that may affect education, upbringing, legal treatment, mental illnesses, etc. for adolescents.

Moral Reasoning and Antisocial Behavior

Neural correlates of moral reasoning and antisocial behavior may be linked, according to Adrian Raine and Yaling Yang at the University of Southern California. Their ideas and research, published in the SCAN (Social Cognitive and Affective Neuroscience) Journal, indicate that the brain regions associated with both moral judgments and antisocial behavior overlap significantly. The brain areas that are compromised in antisocial, violent and psychopathic people and are also activated in moral decision-making (for “normal people”) include the ventral regions of the prefrontal cortex, angular gyrus, and amygdala. Thus, the immoral and abnormal behaviors of antisocial individuals may perhaps be attributed to impairments or disruptions of regions active in moral and cognition and emotion.

Although the research is still lacking with regard to more specific loci within these brain regions and the neural basis for moral processes is yet to be well understood, there are still some interesting points in this article. There could be implications in neuroethics with cases of psychopathic individuals and punishment or justice. Also, further research could possibly contribute to more proper diagnoses of antisocial people and other severe personality disorders with relevant deficiencies.

The Role of the Middle Temporal Visual Area in Slow Driving, Schizophrenia, and Depression

Why are older people generally less astute drivers? To answer this, Professor Duje Tadin and others at the University of Rochester conducted research at the Harvard Medical School that was published in the Journal of Neuroscience. They discovered using transcranial magnetic stimulation (TMS) that the middle temporal visual area (the MT) is responsible for suppressing irrelevant background motion in order to focus more on important motion of smaller foreground objects. Tadin and the team placed magnetic coils at the back of subject’s heads and inhibited the functioning of the MT temporarily by stimulating it for 15 minutes with electrical signals. During this time, they tested how well subjects could identify larger and smaller objects’ motions. They better identified large, background objects’ motions, indicating that a less active or functionally inhibited MT might cause better perception of background motion for older people.

How do they know this? It was previously found that elderly people and schizophrenic or depressed people better perceive background motion. This is due to the brain’s limited power and resources; when more focus is spent on a certain task, there is inevitably less focus on another task using the same resources. Thus, this finding can be useful diagnostically in suggesting or confirming a person’s conditions of schizophrenia or depression, although it seems limited in practical usefulness related to the elderly in general (besides knowledge of the neurobiological reason behind slower driving with age). Hopefully its usefulness in diagnosing such afflictions can also lead to better understanding and treatment of the problems associated with schizophrenia and depression.

Social Emotions and the Amygdala

According to a study conducted by Ralph Adolphs, Simon Baron-Cohen, and Daniel Tranel, amygdala damage causes impaired recognition of social emotions. They tested the recognition of basic emotions, complex mental states, and social emotions from whole faces and eyes using an established set of stimuli. According to this, amygdala damage impairs recognition of emotions in general, but it impairs recognition of complex mental states (thoughtful, quizzical, bored, arrogant, admiring, guilt, flirty) more than basic emotions (happy, sad, angry, etc). Also, it was found that the impairment occurred both when the subjects were shown whole faces and just the eye region. Lastly, the main finding was that damage to the amygdala impairs recognition specifically of social emotions, which were a subset of the complex mental states mentioned above (guilt, arrogance, admiration, flirtatiousness), again by both the whole face and by the eye region.

These findings have certain implications regarding autism. Since autistic people often have impaired recognition of social emotions (similar to subjects in the study), this study’s results suggest that amygdala dysfunction affects social cognition of autistic individuals.

The conclusions from this research seem quite convincing, but it would be interesting to see a wider range of emotions tested, and more specific definitions or methods of assigning traits under categories of “complex mental states” and “social emotions.”