Examples of the simple numerical and arithmetic tasks used in the study. Participants were asked to judge whether the numerical operation was correct or not. Credit: Center for Vital Longevity, University of Texas at Dallas. (up)
A new study by researchers at UT Dallas’ Center for Vital Longevity, Duke University, and the University of Michigan has found that the strength of communication between the left and right hemispheres of the brain predicts performance on basic arithmetic problems. The findings shed light on the neural basis of human math abilities and suggest a possible route to aiding those who suffer from dyscalculia— an inability to understand and manipulate numbers.
It has been known for some time that the parietal cortex, the top/middle region of the brain, plays a central role in so-called numerical cognition—our ability to process numerical information. Previous brain imaging studies have shown that the right parietal region is primarily involved in basic quantity processing (like gauging relative amounts of fruit in baskets), while the left parietal region is involved in more precise numerical operations like addition and subtraction. What has not been known is whether the two hemispheres can work together to improve math performance. The new study demonstrates that they can. The findings were recently published online in Cerebral Cortex.
In the study, conducted in Dallas and led by Dr. Joonkoo Park, now a postdoctoral fellow at Duke University, researchers used functional magnetic resonance imaging, or fMRI, to measure the brain activity of 27 healthy young adults while they performed simple numerical and arithmetic tasks. In one task, participants were asked to judge whether two groups of shapes contained the same or different numbers of items. In two other tasks, participants were asked to solve simple addition and subtraction problems.
Consistent with previous studies, the researchers found that the basic number-matching task activated the right parietal cortex, while the addition and subtraction tasks produced additional activity in the left parietal cortex. But they also found something new: During the arithmetic tasks, communication between the left and right hemispheres increased significantly compared with the number-matching task. Moreover, people who exhibited the strongest connection between hemispheres were the fastest at solving the subtraction problems.
“Our results suggest that subtraction performance is optimal when there is high coherence in the neural activity in these two brain regions. Two brain areas working together rather than either region alone appears to be key” said co-author Dr. Denise C. Park, co-director of the UT Dallas Center for Vital Longevity and Distinguished University Chair in the School of Behavioral and Brain Sciences. Park (no relation to the lead author) helped direct the study along with Dr. Thad Polk, professor of psychology at the University of Michigan.
Lead author Dr. Joonkoo Park points out that the findings suggest that disrupted or inefficient neural communication between the hemispheres may contribute to the impaired math abilities seen in dyscalculia, the numerical equivalent of dyslexia. “If such a causal link exists,” he said, “one very interesting avenue of research would be to develop training tasks to enhance parietal connectivity and to test whether they improve numerical competence.”
Such a training program might help develop math ability in children and could also help older adults whose arithmetic skills begin to falter as a normal part of age-related cognitive decline.
Journal: Cerebral Cortex
You already know it’s hard to balance your checkbook while simultaneously reflecting on your past. Now, investigators at the Stanford University School of Medicine—having done the equivalent of wire-tapping a hard-to-reach region of the brain—can tell us how this impasse arises.
The researchers showed that groups of nerve cells in a structure called the posterior medial cortex, or PMC, are strongly activated during a recall task such as trying to remember whether you had coffee yesterday, but just as strongly suppressed when you’re engaged in solving a math problem.
The PMC, situated roughly where the brain’s two hemispheres meet, is of great interest to neuroscientists because of its central role in introspective activities.
“This brain region is famously well-connected with many other regions that are important for higher cognitive functions,” said Josef Parvizi, MD, PhD, associate professor of neurology and neurological sciences and director of Stanford’s Human Intracranial Cognitive Electrophysiology Program. “But it’s very hard to reach. It’s so deep in the brain that the most commonly used electrophysiological methods can’t access it.”
In a study to be published online Sept. 3 in Proceedings of the National Academy of Sciences, Parvizi and his Stanford colleagues found a way to directly and sensitively record the output from this ordinarily anatomically inaccessible site in human subjects. By doing so, the researchers learned that particular clusters of nerve cells in the PMC that are most active when you are recalling details of your own past are strongly suppressed when you are performing mathematical calculations. Parvizi is the study’s senior author. The first and second authors, respectively, are postdoctoral scholars Brett Foster, PhD, and Mohammed Dastjerdi, PhD.
Much of our understanding of what roles different parts of the brain play has been obtained by techniques such as functional magnetic resonance imaging, which measures the amount of blood flowing through various brain regions as a proxy for activity in those regions. But changes in blood flow are relatively slow, making fMRI a poor medium for listening in on the high-frequency electrical bursts (approximately 200 times per second) that best reflect nerve-cell firing. Moreover, fMRI typically requires pooling images from several subjects into one composite image. Each person’s brain physiognomy is somewhat different, so the blending blurs the observable anatomical coordinates of a region of interest.
Nonetheless, fMRI imaging has shown that the PMC is quite active in introspective processes such as autobiographical memory processing (“I ate breakfast this morning”) or daydreaming, and less so in external sensory processing (“How far away is that pedestrian?”). “Whenever you pay attention to the outside world, its activity decreases,” said Parvizi.
To learn what specific parts of this region are doing during, say, recall versus arithmetic requires more-individualized anatomical resolution than an fMRI provides. Otherwise, Parvizi said, “if some nerve-cell populations become less active and others more active, it all washes out, and you see no net change.” So you miss what’s really going on.
For this study, the Stanford scientists employed a highly sensitive technique to demonstrate that introspective and externally focused cognitive tasks directly interfere with one another, because they impose opposite requirements on the same brain circuitry.
The researchers took advantage of a procedure performed on patients who were being evaluated for brain surgery at the Stanford Epilepsy Monitoring Unit, associated with Stanford University Medical Center. These patients were unresponsive to drug therapy and, as a result, suffered continuing seizures. The procedure involves temporarily removing small sections of a patient’s skull, placing a thin plastic film containing electrodes onto the surface of the brain near the suspected point of origin of that patient’s seizure (the location is unique to each patient), and then monitoring electrical activity in that region for five to seven days—all of it spent in a hospital bed. Once the epilepsy team identifies the point of origin of any seizures that occurred during that time, surgeons can precisely excise a small piece of tissue at that position, effectively breaking the vicious cycle of brain-wave amplification that is a seizure.
Implanting these electrode packets doesn’t mean piercing the brain or individual cells within it. “Each electrode picks up activity from about a half-million nerve cells,” Parvizi said. “It’s more like dotting the ceiling of a big room, filled with a lot of people talking, with multiple microphones. We’re listening to the buzz in the room, not individual conversations. Each microphone picks up the buzz from a different bunch of partiers. Some groups are more excited and talking more loudly than others.”
The experimenters found eight patients whose seizures were believed to be originating somewhere near the brain’s midline and who, therefore, had had electrode packets placed in the crevasse dividing the hemispheres. (The brain’s two hemispheres are spaced far enough apart to slip an electrode packet between them without incurring damage.)
The researchers got permission from these eight patients to bring in laptop computers and put the volunteers through a battery of simple tasks requiring modest intellectual effort. “It can be boring to lie in bed waiting seven days for a seizure to come,” said Foster. “Our studies helped them pass the time.” The sessions lasted about an hour.
On the laptop would appear a series of true/false statements falling into one of four categories. Three categories were self-referential, albeit with varying degrees of specificity. Most specific was so-called “autobiographical episodic memory,” an example of which might be: “I drank coffee yesterday.” The next category of statements was more generic: “I eat a lot of fruit.” The most abstract category, “self-judgment,” comprised sentences along the lines of: “I am honest.”
A fourth category differed from the first three in that it consisted of arithmetical equations such as: 67 + 6 = 75. Evaluating such a statement’s truth required no introspection but, instead, an outward, more sensory orientation.
For each item, patients were instructed to press “1” if a statement was true, “2” if it was false.
Significant portions of the PMC that were “tapped” by electrodes became activated during self-episodic memory processing, confirming the PMC’s strong role in recall of one’s past experiences. Interestingly, true/false statements involving less specifically narrative recall—such as, “I eat a lot of fruit”—induced relatively little activity. “Self-judgment” statements—such as, “I am attractive”—elicited none at all. Moreover, whether a volunteer judged a statement to be true or false made no difference with respect to the intensity, location or duration of electrical activity in activated PMC circuits.
This suggests, both Parvizi and Foster said, that the PMC is not the brain’s “center of self-consciousness” as some have proposed, but is more specifically engaged in constructing autobiographical narrative scenes, as occurs in recall or imagination.
Foster, Dastjerdi and Parvizi also found that the PMC circuitry activated by a recall task took close to a half-second to fire up, ruling out the possibility that this circuitry’s true role was in reading or making sense of the sentence on the screen. (These two activities are typically completed within the first one-fifth of a second or so.) Once activated, these circuits remained active for a full second.
Yet all the electrodes that lit up during the self-episodic condition were conspicuously deactivated during arithmetic calculation. In fact, the circuits being monitored by these electrodes were not merely passively silent, but actively suppressed, said Parvizi. “The more a circuit is activated during autobiographical recall, the more it is suppressed during math. It’s essentially impossible to do both at once.”
A new study published in The Journal of Sexual Medicine reveals that for the first time, stimulation of the vagina, cervix, or clitoris was shown to activate three separate and distinct sites in the sensory cortex.
Some sexuality experts have claimed that the major source of genital sensation is from the clitoris, with relatively little sensation produced by vaginal or cervical stimulation.
Researchers led by Barry R. Komisaruk, B.S., Ph.D., of Rutgers University, used functional magnetic resonance imaging (fMRI) to map sensory cortical responses to clitoral, vaginal, cervical, and nipple self-stimulation in 11 healthy women, ages 23-56. For points of reference on the homunculus (also referred to as the “point-to-point body map” or a diagram showing where nerves from different parts of the body are represented in the brain) researchers also mapped responses to stimulation of the thumb and great toe.
Results found that stimulation of each of these genital regions in fact produces a significant and strong activation of specific and different sites in the sensory cortex.
The three representations are clustered in the same sensory cortical region as the genitals of men on the homunculus.
Nipple self-stimulation activated not only the chest region of the homunculus as expected, but also surprisingly the genital region of the sensory homunculus, suggesting a neurological basis for women’s reports that nipple stimulation feels erotic.
“Our findings demonstrate undeniably that there is a major input to the sensory cortex in response to stimulation of not only the clitoris, but of the vagina and cervix as well, which also evidently receive a significant and substantial sensory nerve supply,” Komisaruk concludes. “This lays the groundwork for an understanding of how genital stimulation spreads sequentially through the brain from initial activation of the sensory cortex to eventually activate the brain regionsthat produce orgasm.”
Irwin Goldstein, editor-in-chief of The Journal of Sexual Medicine, further explained the enormous significance of this ground breaking sexual medicine research. “In the 1930’s-1950’s, researchers localized in the brain exactly where all sensations in man were represented, including male genitalia. Data regarding location of clitoral sensation were only studied in 2010, some sixty years later. This current study in The Journal of Sexual Medicine reveals, for the first time, brain sensation localization data not only from the clitoris, but from the vagina, cervix and nipples. Being able to demonstrate the multiple locations in the brain where stimulation of different female genital regions are represented and how these brain locations inter-relate helps us to better understand women’s sexual function.”
Fluctuations of serotonin levels in the brain, which often occur when someone hasn’t eaten or is stressed, affects brain regions that enable people to regulate anger, new research from the University of Cambridge has shown.
Although reduced serotonin levels have previously been implicated in aggression, this is the first study which has shown how this chemical helps regulate behaviour in the brain as well as why some individuals may be more prone to aggression. The research findings were published September 15, in the journal Biological Psychiatry.
For the study, healthy volunteers’ serotonin levels were altered by manipulating their diet. On the serotonin depletion day, they were given a mixture of amino acids that lacked tryptophan, the building block for serotonin. On the placebo day, they were given the same mixture but with a normal amount of tryptophan.
The researchers then scanned the volunteers’ brains using functional magnetic resonance imaging (fMRI) as they viewed faces with angry, sad, and neutral expressions. Using the fMRI, they were able to measure how different brain regions reacted and communicated with one another when the volunteers viewed angry faces, as opposed to sad or neutral faces.
The research revealed that low brain serotonin made communications between specific brain regions of the emotional limbic system of the brain (a structure called the amygdala) and the frontal lobes weaker compared to those present under normal levels of serotonin. The findings suggest that when serotonin levels are low, it may be more difficult for the prefrontal cortex to control emotional responses to anger that are generated within the amygdala.
Using a personality questionnaire, they also determined which individuals have a natural tendency to behave aggressively. In these individuals, the communications between the amygdala and the prefrontal cortex was even weaker following serotonin depletion. ‘Weak’ communications means that it is more difficult for the prefrontal cortex to control the feelings of anger that are generated within the amygdala when the levels of serotonin are low. As a result, those individuals who might be predisposed to aggression were the most sensitive to changes in serotonin depletion.
Dr Molly Crockett, co-first author who worked on the research while a PhD student at Cambridge’s Behavioural and Clinical Neuroscience Institute (and currently based at the University of Zurich) said: “We’ve known for decades that serotonin plays a key role in aggression, but it’s only very recently that we’ve had the technology to look into the brain and examine just how serotonin helps us regulate our emotional impulses. By combining a long tradition in behavioral research with new technology, we were finally able to uncover a mechanism for how serotonin might influence aggression.”
Dr Luca Passamonti, co-first author who worked on the research while a visiting scientist at the Cognition and Brain Sciences Unit of the Medical Research Council in Cambridge (and currently based at the Consiglio Nazionale delle Ricerche (CNR), Unità di Ricerca Neuroimmagini, Catanzaro), said: “Although these results came from healthy volunteers, they are also relevant for a broad range of psychiatric disorders in which violence is a common problem. For example, these results may help to explain the brain mechanisms of a psychiatric disorder known as intermittent explosive disorder (IED). Individuals with IED typically show intense, extreme and uncontrollable outbursts of violence which may be triggered by cues of provocation such as a facial expression of anger.
“We are hopeful that our research will lead to improved diagnostics as well as better treatments for this and other conditions.”
This study was supported by the James S. McDonnell Foundation
Luca Passamonti, Molly J. Crockett, Annemieke M. Apergis-Schoute, Luke Clark, James B. Rowe, Andrew J. Calder, Trevor W. Robbins. Effects of Acute Tryptophan Depletion on Prefrontal-Amygdala Connectivity While Viewing Facial Signals of Aggression. Biological Psychiatry, 13 September 2011 DOI:10.1016/j.biopsych.2011.07.033