Culture Shapes Arithmetic in the Brain

A collaborative study by Chinese and American authors has suggested that our mother tongue might influence the development of the brain circuits involved in processing numbers and arithmetic. They used Arabic digits (a symbol system shared by both languages, rather than phonological or orthographic symbols) to present simple problems (as in 3 + 4 = ?). Using functional MRI, they demonstrated a differential cortical representation of numbers between native Chinese and English speakers (NCS and NES). Contrasting to native English speakers, who largely employ a language process that relies on the left perisylvian cortices for mental calculation such as a simple addition task, native Chinese speakers, instead, engage a visuo-premotor association network for the same task.

"Remarkable differences between NES and NCS were found during the condition of Number representation, especially in the left hemisphere ( B and D). The activation in NES is greater in the left SMA, Broca area, and Wernicke area (Wn), compared with the corresponding areas in NCS. Meanwhile, the occipito-parietal pathway, sensorimotor areas (including the cerebellum), as well as the frontal cortex, show a similar level of activation for both NCS and NES during the Number condition, which is congruent with the suggestion that the classical number-processing model involves verbal, analogue, and visual components. Importantly, much larger brain activation was found at a region in-between BA6, BA8, and BA9 in NCS. We termed this region as a premotor association area (PMA), which has been previously associated with visuo-spatial processing and various functions more closely related to cognitive than to motor processes in humans and nonhuman primates as well."

The authors note that, in addition to mother tongue, it is possible that different teaching methods across cultures, or variations in genetic disposition, could also prime the brains of Chinese and English speakers to solve mathematical equations in different ways.

MRI Detection of Brain Awareness in the Vegetative State

A fascinating report by Owen et al in Science documents one case in which a woman, completely unresponsive and diagnosed as being in a vegetative state, showed responses in her language and motor brain areas that were indistinguishable from normal. From a review by Miller: "Five months after an auto accident, she was unresponsive, unable to communicate, and met the clinical criteria for vegetative state. However, fMRI scans showed that language-processing regions of her brain became active when words were spoken to her but not when she was exposed to nonspeech sounds. Sentences containing ambiguous words such as "creek/creak" activated additional language regions, as they do in healthy people. These findings indicated that she retained some ability to process language... In another test, the researchers instructed the woman to picture herself playing tennis or walking through her house. In healthy people, imagining each activity activates a different set of brain areas involved in planning movements. The patient's fMRI scans showed an identical pattern--clear evidence, Owen and colleagues say, that she made a conscious decision to follow their instructions."

"Although some researchers aren't convinced Owen's team has cinched the case for consciousness in this woman, most agree that the fMRI scans reveal evidence of cognition that could not have been anticipated from standard MRI scans....Owen hopes to build on this work to develop a battery of fMRI tests for measuring cognitive functions in brain-damaged patients who are unable to communicate. He says this approach might someday be used to customize a patient's rehabilitation. For instance, if a patient's fMRI scans revealed an incapacitated visual system but a working auditory system, therapists could employ speech and sound."

Fatherhood changes the prefrontal cortex.

Like human fathers, male marmosets help raise their young. Neuroimaging studies show that stimuli related to one's own child activate the anterior paracingulate and orbitofrontal areas of the prefrontal cortex (PFC). The PFC shows structural plasticity in adulthood and contains receptors for several neuropeptides implicated in parental behavior, such as vasopressin, oxytocin and prolactin. Kozorovitskiy et al now report in Nature Neuroscience that first-time and experienced marmoset fathers have enhanced density of dendritic spines on pyramidal neurons in prefrontal cortex as compared to non-fathers. In parallel, the abundance of vasopressin V1a receptors and the proportion of V1a receptor–labeled dendritic spines increase. How this links to function and behavior is not known, and it would be interesting to see if similar changes are seen in the brains of nonparental caregivers (since marmosets breed cooperatively).

Left) Marmoset father carrying infants. Right) Pyramidal neuron of a marmoset father, with close-up views of apical (a) and basal (b) dendrites.

God on the Brain

The Economist has a nice review and critical discussion of work by Mario Beauregard and collaborators at the Univ. of Montreal doing fMRI imaging of the brains of Carmelite nuns as they recall experiences of mystical union (by definition such experiences can not be summoned at will). The idea is based on the fact that imagining an experience usually activates the same brain regions that are active when the experience is actually taking place. Not surprisingly, there is no "God spot" in the brain, and activity in a number of brain regions, notably emotional areas, correlates with the recall of union. From their abstract in Neuroscience Letters (Volume 405, Issue 3 , 25 September 2006): "The brain activity of Carmelite nuns was measured while they were subjectively in a state of union with God. This state was associated with significant loci of activation in the right medial orbitofrontal cortex, right middle temporal cortex, right inferior and superior parietal lobules, right caudate, left medial prefrontal cortex, left anterior cingulate cortex, left inferior parietal lobule, left insula, left caudate, and left brainstem. Other loci of activation were seen in the extra-striate visual cortex. These results suggest that mystical experiences are mediated by several brain regions and systems."

Brain imaging has been to used to study a number of other altered states of consciousness, such as the phantom limb phenomenon and out of body experiences. Brain damage in the region of junction of the temporal and parietal lobes can alter perception of personal and extrapersonal space, and other studies have shown the changes in activation in this region correlates with meditative experiences of sensing sensing a greater interconnectedness of things, and dissolution of self into some larger entity.

The central role of "construals" in determining performance... the power of brief interventions

An article in the Sept. 1 issue of Science by Cohen et. al. and an accompanying review by Wilson point out the power of brief interventions that change people's self- and social perceptions.

You may... "undoubtedly be surprised, or even incredulous, that a 15-min intervention can reduce the racial achievement gap by 40%. Yet this is precisely what Cohen et al. .... African American seventh graders randomly assigned to write about their most important values achieved significantly better end-of-semester grades than students in a control condition. How can this be?"

The table shows the result of this and similar studies (click to enlarge):

Legend: Brief theory-based interventions improved students' grades [increases shown on a four-point grade point average (GPA) scale, relative to randomly assigned control groups].

"The Cohen et al. study and the others like it illustrate key social psychological points. It can be as important to change people's "construals"--their interpretations of the social world and their place in it--as it is to change the objective environment....It is not clear why students in the Cohen et al. sample failed to self-affirm on their own. Why did it take an in-class essay to focus students' attention on values that were important to them? Issues of generalizability also arise, such as whether the self-affirmation exercise would work with younger age groups."

Seligman's Happiness Regimen...

An article in the August issue of Discover Magazine discusses whether we can train ourselves to be happy. Classes are now taught on obtaining happiness, and utilize such exercises as writing and reciting a "gratitude" letter to a friend and jotting down three happy events of each day every night for a week. Instead of trying to figure out why you are sad, the emphasis is on training the mind to focus on the past as being very positive.


credit: Discover Magazine

The article focuses on an interview with Martin Seligman, who coined the term positive psychology in 1998 when he was president of the American Psychological Association. The association's official journal devoted its entire January 2000 issue to the subject. Some 350 psychologists from 23 countries attended the seventh annual Positive Psychology International Summit last October; as evidence of the movement's mainstream credentials, the next one, this fall, is cosponsored by Toyota. You can now subscribe to the Journal of Happiness Studies and buy one of Seligman's best-selling books, like Authentic Happiness or Learned Optimism.

...Happiness is a surprisingly contentious subject, and at least some psychologists argue that "think positive" exhortations should be left to pop purveyors like Norman Vincent Peale and Tony Robbins. "We live in a culture that already expects you to be happy all the time. I call it the tyranny of the positive attitude," grouses Barbara Held, professor of psychology at Bowdoin College and the author of Stop Smiling, Start Kvetching. In Held's view, having the positive psychology movement throw its weight behind that cultural bias serves up a double whammy: People who feel bad must now shoulder the added weight of feeling defective for feeling bad. "People say we are trying to tell people what kind of lives to lead," Seligman responds. "But I'm old-fashioned about science. I think science needs to be descriptive. I am just trying to describe." He wants to leave the choice of whether to follow to others.

You might enjoy having a look at the the Positive Psychology Center and Authentic Happiness wesites.

The Expert Mind

I've been meaning to mention an interesting article in the August issue of Scientific American, by Philip Ross, on how people become experts in different fields of accomplishment.

Some clips ard paraphrase from that article: Some of the most clear research on expertise has studied skill at chess, which can be clearly measured. What emerges is that the expert relies not so much on an intrinsically stronger power of analysis as on a store of structured knowledge. Similar results have been demonstrated in bridge players (who can remember cards played in many games), computer programmers (who can reconstruct masses of computer code) and musicians (who can recall long snatches of music). Ability in one area tends not to transfer to another. American psychologist Edward Thorndike first noted this lack of transference over a century ago, when he showed that the study of Latin, for instance, did not improve command of English and that geometric proofs do not teach the use of logic in daily life.


Figure from Amidzic et al. (2001) Brain activity in chess masters is different from the pattern observed in novices. Relationship between chess-playing skill (Elo rating scale) and the relative share of dipoles located in medial temporal lobe structures (black) and in the frontal and parietal cortices (red). In weaker players more activfity occurred in the brain's medial temporal lobe than in the frontal and parietal cortices, which suggests that the amateurs were analyzing unusual new moves. In gradmasters, however, the frontal and parietal cortices were more active, indicating that they were retrieving information from long term memory.

It takes enormous effort to build these structures in the mind. Herbert Simon coined a psychological law of his own, the 10-year rule, which states that it takes approximately a decade of heavy labor to master any field. Even child prodigies, such as Gauss in mathematics, Mozart in music and Bobby Fischer in chess, must have made an equivalent effort, perhaps by starting earlier and working harder than others. K.A. Ericsson argues that what matters is not experience per se but "effortful study," which entails continually tackling challenges that lie just beyond one's competence...Having reached an acceptable performance--for instance, keeping up with one's golf buddies or passing a driver's exam--most people relax. Their performance then becomes automatic and therefore impervious to further improvement. In contrast, experts-in-training keep the lid of their mind's box open all the time, so that they can inspect, criticize and augment its contents and thereby approach the standard set by leaders in their fields...

At this point, many skeptics will finally lose patience. Surely, they will say, it takes more to get to Carnegie Hall than practice, practice, practice. Yet this belief in the importance of innate talent, strongest perhaps among the experts themselves and their trainers, is strangely lacking in hard evidence to substantiate it...motivation appears to be a more important factor than innate ability in the development of expertise. It is no accident that in music, chess and sports--all domains in which expertise is defined by competitive performance rather than academic credentialing--professionalism has been emerging at ever younger ages, under the ministrations of increasingly dedicated parents and even extended families.

Neural operations that give rise to a unitary sense of self.

An interesting article by Moran et. al. in Journal of Cognitive Neuroscience: They examined whether the cognitive and affective components of self-reflection can be dissociated using functional magnetic resonance imaging. Using a simple paradigm in which subjects judged the personal relevance of personality characteristics that were either favorable (e.g., "honest") or unfavorable (e.g., "lazy"), they found that distinct neural circuits in adjacent regions of the prefrontal cortex subserve cognitive and emotional aspects of self-reflection. The medial prefrontal cortex responded only to material that was self-descriptive, and this did not differ as a function of the valence of the trait. When material was judged to be self-relevant, the valence of the material was resolved in an adjacent region of ventral anterior cingulate.


Figure Legend: Whole-brain ANOVA analysis revealed a main effect of self-relevance (top left) in the medial prefrontal cortex (MPFC) and posterior cingulate cortex (pCC), a main effect of valence (top right) in the ventral anterior cingulate cortex (vACC), and a self-relevance by valence interaction (bottom left) in the vACC, the dorsal anterior cingulate cortex (dACC), and the supplementary motor area (SMA). To qualitatively identify whether brain regions identified in the ANOVA analysis showed a strong bias toward one of the two main effects, a self-relevance/valence sensitivity measure (F ratio) was computed on a voxel-by-voxel basis by dividing the self-relevance F score for each voxel by the valence F score. Voxels that did not yield a significant main effect of either self-relevance or valence were excluded from further analysis to avoid spurious F ratio effects. To facilitate visualization of this sensitivity measure, F ratios were transformed to a logarithmic scale. Voxels that were more sensitive to trait valence yielded negative values (blue color scale), whereas voxels that were more sensitive to self-relevance yielded positive values (yellow color scale). Voxels at the tail end of the color scales were those voxels that exhibited the greatest bias toward trait valence and self-relevance, respectively. Voxels in the MPFC (BA 10) and two regions of the pCC (BA 29/30 and BA 23) demonstrated greater sensitivity to self-relevance, whereas voxels in the vACC (BA 25) demonstrated greater sensitivity to trait valence.

Avoiding Punishment is its Own Reward...

Work by Kim et al employs functional imaging to suggest a similar role for the human medial orbitofrontal cortex in processing the receipt of a reward and the successful avoidance of an aversive outcome.


Figure: Medial OFC showing a significant increase in activity after avoidance of an aversive outcome as well as after obtaining reward. No other brain areas showed significant effects at p < 0.001.

These results are compatible with the possibility that activity in the medial OFC during avoidance reflects an intrinsic reward signal that serves to reinforce avoidance behavior. Activity in the medial OFC not only increased after avoiding an aversive outcome or receiving reward, but also decreased after failing to obtain a reward or receiving an aversive outcome. Consequently, this region shows a fully opponent response profile to rewarding and aversive outcomes and their omission.

Making faces in the brain

Some regions of the inferior temporal cortex (IT) respond with high selectivity to faces. Afraz et al. have shown a causal link between activity of these region and actual face perception measured behaviorally. Artificially activating the right neurons at the right time causes visual perception of a face. This new result shows that such neurons directly underlie the recognition of complex objects. Their abstract:

"The inferior temporal cortex (IT) of primates is thought to be the final visual area in the ventral stream of cortical areas responsible for object recognition. Consistent with this hypothesis, single IT neurons respond selectively to highly complex visual stimuli such as faces. However, a direct causal link between the activity of face-selective neurons and face perception has not been demonstrated. In the present study of macaque monkeys, we artificially activated small clusters of IT neurons by means of electrical microstimulation while the monkeys performed a categorization task, judging whether noisy visual images belonged to 'face' or 'non-face' categories. Here we show that microstimulation of face-selective sites, but not other sites, strongly biased the monkeys' decisions towards the face category. The magnitude of the effect depended upon the degree of face selectivity of the stimulation site, the size of the stimulated cluster of face-selective neurons, and the exact timing of microstimulation. Our results establish a causal relationship between the activity of face-selective neurons and face perception."

Evidence for stroke-induced neurogenesis in the human brain

The Work of Bhardwaj et. al. mentioned in the Aug. 22 blog posting has made the point that under normal conditions new neurons are not born at detectable levels in the adult human brain. These measurements had a detection limit of ~ 1%, however, and would not have been expected to note small amounts of nerve cell proliferation occurring near areas damaged by stroke. Jin et al. now report in PNAS that in patients with stroke, cells that express markers associated with newborn neurons are present in the ischemic penumbra surrounding cerebral cortical infarcts, where these cells are preferentially localized in the vicinity of blood vessels. These findings suggest that stroke-induced compensatory neurogenesis may occur in the human brain, where it could contribute to postischemic recovery and represent a target for stroke therapy.

Start your own religion....

The invention of religions is a universal characteristic of human cultures. An article by Michael Luo in the Aug. 28 New York Times describes an interesting film project attempting to follow one example. Andy Deemer's film project placed advertisements seeking participants for a very real, albeit unusual, social experiment: take $5,000 to start your own religious movement, in exchange for allowing a film crew to follow you around as you try to get under way. It turns out that 40 to 45 new religious groups are emerging a year, compared with just a handful a year a little over a century ago. The New York City area has long been a hotbed for new religions, as well as the staging ground for overseas religious movements trying to make the leap into America. New religions tend to form in urban areas, where it is much easier to gather an initial group. Some of the movements that began in this country in the New York City area include Hare Krishna, modern incarnations of Wicca and an array of guru-centered groups. Other successful movements include Scientology, probably the most successful religion of the past century; Unification Church, led by the Rev. Sun Myung Moon; Church Universal and Triumphant, a New Age group; and the Universal Life Church.

After interviewing candidates who ranged from genuine to humorous to bizarre, Joshua Boden (35) was chosen to attempt to establish his "Church of Now", a God-optional religion that lists 14 precepts, including, “The only ‘sin’ is not living fully,” and, “This life is the one that counts; this IS your eternal reward.” The religion has elements of Buddhism, Taoism and New Age thinking. Although some of the beliefs might sound unorthodox and nonreligious (“Laughter is a must!”), Mr. Boden is earnest in his beliefs and his desire to establish a spiritual community. The going as been rocky so far. Potential followers indicated the presentation was not persuasive and authoritative ("Believe this!") enough.

More on the impulsive teenage brain

Nature has a feature by Kendall Powell on how teenage brain's work (see also my 7/07 post). Abstracting from that review:

An NIMH research team, led by Jay Giedd, has made a movie of normal brain changes from ages 5 to 20. It reveals that the grey matter thickens in childhood but then thins in a wave that begins at the back of the brain and reaches the front by early adulthood (see movie, below). The process completes itself sooner in girls than in boys. This corresponds to a long-held assumption that adolescence sees the prefrontal cortex regions that handle executive functions 'waking up' and to the conventional wisdom that girls mature faster in this respect.
(Click on the thin rectangular box below this line if you want to start the movie)

A reward centre on overdrive coupled with planning regions not yet fully functional could make an adolescent an entirely different creature to an adult when it comes to seeking pleasure. In adolescents given a medium or large reward, the nucleus accumbens (part of the reward center of the brain) reacts more strongly than in children or adults

A speculation is that the lag between the frontal regions and the reward centre is an evolutionary feature, not a bug. "You need to engage in high-risk behaviour to leave your village and find a mate," and risk-taking soars at just the same time as hormones drive adolescents to seek out sexual partners.... in rodents, primates and even some birds, adolescence is a time of risky business, seeking out same-age peers and fighting with parents, which "all help get the adolescent away from the home territory".

"I don't think we can fight the biology of wanting to take risks and try on different identities. ...As a society, we can give kids creative, positive outlets that do not lead to irreversible mistakes...Attempts to push kids towards safe sex or pharmaceutical temperance shouldn't be expected to succeed if they simply explain consequences....Adolescents have some fundamental qualities to them that are not voluntary and not easily modified by rational, information-based interventions."

A warning...prenatal ultrasound waves disrupt embryonic brain cell migration in mice.

Ang et al report: Neurons of the cerebral neocortex in mammals, including humans, are generated during fetal life in the proliferative zones and then migrate to their final destinations by following an inside-to-outside sequence. The present study examined the effect of ultrasound waves (USW) on neuronal position within the embryonic cerebral cortex in mice. We used a single BrdU injection to label neurons generated at embryonic day 16 and destined for the superficial cortical layers. Our analysis of over 335 animals reveals that, when exposed to USW for a total of 30 min or longer during the period of their migration, a small but statistically significant number of neurons fail to acquire their proper position and remain scattered within inappropriate cortical layers and/or in the subjacent white matter. The magnitude of dispersion of labeled neurons was variable but systematically increased with duration of exposure to USW. These results call for a further investigation in larger and slower-developing brains of non-human primates and continued scrutiny of unnecessarily long prenatal ultrasound exposure.

Are you beautiful??

The following is from a curious website "Beauty Check" at the Univ. of Regensberg, Germany. A summary of the research is given there.

Here are the composite prototypes they offer:






Characteristics of the male "Sexy face" in the comparison to the "unsexy face":

* Browner skin
* Narrower facial shape
* Less fat
* Fuller and more symmetrical lips
* Darker eye brows
* More and darker lashes
* Upper half of the face broader in relation to the lower
* Higher cheek bones
* Prominent lower jaw
* More prominent chin
* No receding brows
* Thinner lids
* No wrinkles between nose and corner of the mouth





Characteristic features of the female "sexy face" in comparison to the "unsexy face":

* Suntanned skin
* Narrower facial shape
* Less fat
* Fuller lips
* Slightly bigger distance of eyes
* Darker, narrower eye brows
* More, longer and darker lashes
* Higher cheek bones
* Narrower nose
* No eye rings
* Thinner lids

Modulation of competing memory systems by distraction

Foerde et al. show that the relative contributions to a learning task of the declarative memory system of the medial temporal lobe (including the hippocampus) and the habit learning system of the striatum (including basal ganglia) can be altered by the presence of a secondary task during learning. If distractions cause the learning to decrease the relative involvement of the declarative system relative to the habit system, then the resulting learning is not as flexibly applied in new situations:

"Different forms of learning and memory depend on functionally and anatomically separable neural circuits [Squire, L. R. (1992) Psychol. Rev. 99, 195–231]. Declarative memory relies on a medial temporal lobe system, whereas habit learning relies on the striatum [Cohen, N. J. & Eichenbaum, H. (1993) Memory, Amnesia, and the Hippocampal System (MIT Press, Cambridge, MA)]. How these systems are engaged to optimize learning and behavior is not clear. Here, we present results from functional neuroimaging showing that the presence of a demanding secondary task during learning modulates the degree to which subjects solve a problem using either declarative memory or habit learning. Dual-task conditions did not reduce accuracy but reduced the amount of declarative learning about the task. Medial temporal lobe activity was correlated with task performance and declarative knowledge after learning under single-task conditions, whereas performance was correlated with striatal activity after dual-task learning conditions. These results demonstrate a fundamental difference in these memory systems in their sensitivity to concurrent distraction. The results are consistent with the notion that declarative and habit learning compete to mediate task performance, and they suggest that the presence of distraction can bias this competition. These results have implications for learning in multitask situations, suggesting that, even if distraction does not decrease the overall level of learning, it can result in the acquisition of knowledge that can be applied less flexibly in new situations."

The Buddha's Biology

I want to mention a book by that I have found to be a useful summary and distillation of correspondences between classical Buddhist psychology and modern psychology and evolutionary biology. Don't let its self-helpy new-agey title put you off (Buddha's Nature: A Practical Guide to Discovering Your Place in the Cosmos). It's by a crazy guy named Wes Nisker, a stand up Buddhist comic and veteran of the sixties and seventies new age San Francisco scene whose other writings include "The Big Bang, The Buddha, and the Baby Boom" and "The Essential Crazy Wisdom". It is a largely accurate descriptions of how Buddhism's four foundations of mindfulness can be taken to correspond to the bottom-up construction of our nervous system and consciousness, and to stages in the evolution of our nervous systems.

Sensing or exploring the nature of our elemental physical existence, our body breathing and homeostasis, is a focus of the Buddha's First Foundation of Mindfulness. This first foundation corresponds to physical elements of the body and homeostasis (regulation of blood flow, body temperature, etc.) These functions center in primitive brain stem structures we share with reptiles and other vertebrates. This core regulates interactions with the physical world elemental to having a self that we seldom think about - like breathing, supporting ourselves against gravity, seeing, tasting, smelling, touching, hearing.

These core structures also regulate our urge to remedy hunger, to have sex, to approach or avoid, to flee or fight when suddenly presented with very threatening situations. Our experience of these primary and instinctual basic drives, in its urgency and automaticity, has a very different quality than our experience of thoughts or more complicated emotions. The Buddha's Second Foundation of Mindfulness rests on the sentience of the nervous system which can note these elemental feelings, impressions of pleasant/unpleasant/neutral/painful, etc. We can, in more quiet moments of reflection or meditation note the more muted `flickers' of these primal forces, appearing and disappearing almost as transient quantal energies.

Our human introspective access to, observation of, emotional feelings more nuanced than the basic drives mentioned above is the focus of the Buddha's third foundation of mindfulness (affection, fear, anger, sadness, playfulness, etc.). These are regulated by a new kind of cortex that appears in mammals between the brain stem and the outer layer of the cortex, usually referred to as the limbic system.

Finally, our higher level cognitive abilities associated with the newer cortex (neocortex) that forms the top layers or our brain - our ability to note how thoughts and feelings are produced, as natural occurrences like breathing or the heartbeat - are a focus of the Buddha's fourth foundation of mindfulness.

Nisker's book has several sections of exercises or meditations useful in sensing layers of the self, its evolutionary nature, and its symbiosis with the external social and physical world.

An RNA gene expressed during cortical development evolved rapidly in humans

I can't say it any better than the abstract by Pollard et al. does:

"The developmental and evolutionary mechanisms behind the emergence of human-specific brain features remain largely unknown. However, the recent ability to compare our genome to that of our closest relative, the chimpanzee, provides new avenues to link genetic and phenotypic changes in the evolution of the human brain. We devised a ranking of regions in the human genome that show significant evolutionary acceleration. Here we report that the most dramatic of these 'human accelerated regions', HAR1, is part of a novel RNA gene (HAR1F) that is expressed specifically in Cajal–Retzius neurons in the developing human neocortex from 7 to 19 gestational weeks, a crucial period for cortical neuron specification and migration. HAR1F is co-expressed with reelin, a product of Cajal–Retzius neurons that is of fundamental importance in specifying the six-layer structure of the human cortex. HAR1 and the other human accelerated regions provide new candidates in the search for uniquely human biology."

The work suggests that protein-coding genes may not be the movers and shakers of human evolution. Rather, the non-coding 'dark matter' of genomes may harbour most of these vital changes, such as the set of 49 HAR regions - with HAR1 having accrued 18 changes in sequence since our divergence from chimpanzees, whereas only 1 or 2 substitutions would have been expected by chance.

No more new neurons for you: Stable neuron numbers from cradle to grave

These are the titles of a review in PNAS and another in Science of a PNAS paper by Bhardwaj et al. that unequivocally settles a hotly contested issue. It had been reported that a large number of neurons stream daily from proliferative layers near the cerebral ventricle to the overlaying neocortex in adult nonhuman primates, raising speculation that new neurons are continuously added to the adult human cerebral cortex. However, this finding could not be confirmed in either the primate or rodent cortex. Bhardwaj et al. took advantage of the integration of 14C, generated by nuclear bomb tests during the Cold War, in DNA to establish the age of neurons in the major areas of the human cerebral neocortex. Together with the analysis of the neocortex from patients who received BrdU, which integrates in the DNA of dividing cells, their results demonstrate that, whereas nonneuronal cells turn over, neurons in the human cerebral neocortex are not generated in adulthood at detectable levels but are generated before birth.

Thus new neurons are not born in the adult human brain, and changes required for memory, learning, and injury repair must involve alterations or growth of connections between existing nerve cells.

Twin Valley Classical Piano Music

Totally unrelated to the subject area of this blog, but for those of you who know me I thought I would mentioned that I've started to put some of the 2006 classical piano recordings that I am doing on this website.