Plasticity of gender difference in math performance

My Sept. 11 post mentioned studies of how construals can influence performance. Another example comes now from Dar-Nimrod and Heine, who manipulated participants' beliefs regarding the source of gender differences in math and measured their subsequent math performance (see figure). In study 1 (7), women undertook a Graduate Record Exam–like test in which they completed two math sections separated by a verbal section. The verbal section contained the manipulation in the form of reading comprehension essays. Each test condition used a different essay. Two of the essays argued that math-related sex differences were due to either genetic (G) or experiential causes (E). Both essays claimed that there are sex differences in math performance of the same magnitude. Two additional essays served as a traditional test of stereotype threat. One essay, designed to eliminate underperformance, argued that there are no math-related gender differences (ND). The other essay, designed as a standard stereotype-threat manipulation (S), primed sex without addressing the math stereotype. Controlling for performance on the first math section, they used analyses of covariance to demonstrate that women in the G and the S conditions exhibited similar performances on the second math test. Women in the E and the ND conditions, although not different from each other, significantly outperformed women in G and S conditions).



Click to enlarge figure. Legend: (Left) Study 1 results (133 women). Scores on second math test (controlling for scores on first test) after reading essays. (Right) Study 2 results (92 women), used a slightly different protocol (see methods)

These studies demonstrate that stereotype threat in women's math performance can be reduced, if not eliminated, when women are presented with experiential accounts of the origins of stereotypes. People appear to habitually think of some sex differences in genetic terms unless they are explicitly provided with alternative experiential arguments.

Imaging the brain during the motivated reasoning of political bias

Westen et al. report studies using functional neuroimaging to study the neural responses of 30 committed partisans during the U.S. Presidential election of 2004. They presented subjects with reasoning tasks involving judgments about information threatening to their own candidate, the opposing candidate, or neutral control targets. Motivated reasoning was associated with activations of the ventromedial prefrontal cortex, anterior cingulate cortex, posterior cingulate cortex, insular cortex, and lateral orbital cortex. As predicted, motivated reasoning was not associated with neural activity in regions previously linked to cold reasoning tasks and conscious (explicit) emotion regulation. The findings provide the neuroimaging evidence for phenomena variously described as motivated reasoning, implicit emotion regulation, and psychological defense. They suggest that motivated reasoning is qualitatively distinct from reasoning when people do not have a strong emotional stake in the conclusions reached.


Figure legend - Subjects' ratings of perceived contradictions in statements by Bush, Kerry, and neutral figures (higher ratings indicate greater perceived contradictions). Democrats and Republicans reasoned to distinctly different conclusions about their preferred candidates, with mirror-image responses: Democrats readily identified the contradictions in Bush's statements but not Kerry's, whereas Republicans readily identified the contradictions in Kerry's statements but not Bush's. In contrast, Democrats and Republicans reasoned similarly about the contradictions of politically neutral figures.


One of several figures showing imaging data - Three orthogonal views (axial, sagittal, coronal) of the areas of activation that differed when subjects were confronted with contradictory (threatening) information regarding their own party's candidate versus a neutral target person. ACC = anterior cingulate; mPFC = medial prefrontal cortex; pCING = posterior cingulate; PCU = precuneus; vmPFC = ventromedial prefrontal cortex.

Human fronto–mesolimbic networks guide decisions about charitable donation

Humans often sacrifice material benefits to endorse or to oppose societal causes based on moral beliefs. Charitable donation behavior, which has been the target of recent experimental economics studies, is an outstanding contemporary manifestation of this ability. Yet the neural bases of this unique aspect of human altruism, which extends beyond interpersonal interactions, remain obscure. Moll et al. have used functional magnetic resonance imaging while participants anonymously donated to or opposed real charitable organizations related to major societal causes. They show that the mesolimbic reward system is engaged by donations in the same way as when monetary rewards are obtained.
Furthermore, medial orbitofrontal–subgenual and lateral orbitofrontal areas, which also play key roles in more primitive mechanisms of social attachment and aversion, specificalculy mediate decisions to donate or to oppose societal causes. More anterior sectors of the prefrontal cortex are distinctively recruited when altruistic choices prevail over selfish material interests.


Figure - Brain responses for monetary reward and donation. (a) Mesolimbic–striatal reward system, including the VTA and the dorsal and ventral sectors of the striatum (STR), activation for both pure monetary reward and noncostly donation (conjunction of pure reward vs. baseline and noncostly donation vs. baseline). (b) Subgenual area (SG) activation for decisions to donate (conjunction of costly and noncostly conditions) as compared with pure monetary reward.


Figure - Brain responses for opposition and costly decisions. (a) lOFC responses to decisions to oppose causes as compared with decisions involving pure monetary reward (conjunction of costly and noncostly conditions). (b) Comparison of costly decisions (sacrificing money either to donate or to oppose causes) to pure monetary rewards. Effects were observed in the anterior prefrontal cortex (aPFC), including the frontopolar cortex and the medial frontal gyrus (BA 10/11/32), and in the dorsal anterior cingulate cortex (dACC).

Early exposure to novelty enhances social, cognitive, and neuroendocrine development

An interesting article in the latest PNAS from the University of New Mexico and McEwen's laboratory at Rockefeller.... I can't say it any better than the (slightly edited) abstract does:

Mildly stressful early life experiences can potentially impact a broad range of social, cognitive, and physiological functions in humans, nonhuman primates, and rodents. Recent rodent studies favor a maternal-mediation hypothesis that considers maternal-care differences induced by neonatal stimulation as the cause of individual differences in offspring development. Using neonatal novelty exposure, a neonatal stimulation paradigm that dissociates maternal individual differences from a direct stimulation effect on the offspring, Tang et al. investigated the effect of early exposures to novelty on a diverse range of psychological functions using several assessment paradigms. Pups that received brief neonatal novelty exposures away from the home environment showed enhancement in spatial working memory, social competition, and corticosterone response to surprise during adulthood compared with their home-staying siblings. These functional enhancements in novelty-exposed rats occurred despite evidence that maternal care was directed preferentially toward home-staying instead of novelty-exposed pups, indicating that greater maternal care is neither necessary nor sufficient for these early stimulation-induced functional enhancements. The authors suggest a unifying maternal-modulation hypothesis, which distinguishes itself from the maternal-mediation hypothesis in that (i) neonatal stimulation can have direct effects on pups, cumulatively leading to long-term improvement in adult offspring; and (ii) maternal behavior can attenuate or potentiate these effects, thereby decreasing or increasing this long-term functional improvement.

Your Brain on Humor...an fMRI study

A popular psychological model suggests that humor involves detection and resolution of incongruity. Incongruity is generated when a prediction is not confirmed in the final part of a story. To comprehend humor, it is necessary to revisit the story, transforming an incongruous situation into a funny, congruous one. Bartolo et al. used cartoon pairs to elicit humor without language processing because previous studies involving verbal humor had been difficult to interpret.

Here is the cartoon pair:



They found activation of both the left and the right hemispheres when comparing funny versus nonfunny cartoons. In particular, as shown in Part A of the figure below, they found activation of the right inferior frontal gyrus (Brodman area 47, BA 47), the left superior temporal gyrus (BA 38), the left middle temporal gyrus (BA 21), and the left cerebellum. These areas had previously been implicated in a nonverbal task exploring attribution of intention. They suggest that the resolution of incongruity might occur through a process of intention attribution. Bartolo et al. also asked subjects to rate the funniness of each cartoon pair. A parametric analysis of Brain areas activated during humor appreciation (Part B of figure below)showed that the left amygdala (the small dot in center of the top two pictures in part B) was activated in relation to subjective amusement, suggesting a key role for the amygdala in giving humor an emotional dimension.

A genetic change in brain growth factor alters anxiety behavior in mice (and humans?)

Brain derived neurotrophic factor (BDNF) regulates neuronal survival, differentiation, and synaptic plasticity. There has been speculation that its genetic alteration might contribute to affective and anxiety disorders. A report by Chen et al. in the Oct. 6 issue of Science now shows that a genetic mutation in humans that changes a single amino acid (valine to methionine) in BDNT can be reproduced in transgenic mice. Transgenic mice heterozygous for the Met allele, like humans, have smaller hippocampal volumes and perform poorly on hippocampal-dependent memory tasks.

Subsequent analyses of these mice elucidated a phenotype that had not been established in human carriers: increased anxiety. When placed in conflict settings, transgenic mice homozygous for the Met allele displayed increased anxiety-related behaviors in three separate tests, suggesting a genetic link between BDNF and anxiety. Some genetic association studies in humans have found that the Met allele has been associated with increased trait anxiety, but other studies have not replicated these findings. The anxiety-related phenotype may have been easier to observe in mice for two reasons: First, mice were subjected to conflict tests to elicit the increased anxiety-related behavior, whereas human studies relied on questionnaires. Second, the anxiety-related phenotype was only present in mice homozygous for the Met allele, which suggested that association studies that focused primarily on humans heterozygous for the Met allele may not detect an association. In this context, another human genetic polymorphism in the serotonin transporter (5HTLPR) is associated with depression only in homozygote subjects with past trauma histories.

A neural network that shares a common genetic origin with human intelligence.

Pol et al. have explored the genetic influence on focal gray matter (GM, nerve cell bodies) and white matter (WM, myelin covered axon tracts) densities in magnetic resonance brain images of 54 monozygotic and 58 dizygotic twin pairs and 34 of their siblings. To explore the common genetic origin of focal GM and WM areas with intelligence, they obtained cross-trait/cross-twin correlations in which the focal GM and WM densities of each twin are correlated with the psychometric intelligence quotient of his/her cotwin. They found genes to significantly influence WM density of the superior occipitofrontal fascicle, corpus callosum, optic radiation, and corticospinal tract, as well as GM density of the medial frontal, superior frontal, superior temporal, occipital, postcentral, posterior cingulate, and parahippocampal cortices. Moreover, their results showed that verbal (VIQ) and nonverbal (performance) (PIQ) intelligence quotient share a common genetic origin with an anatomical neural network involving the frontal, occipital, and parahippocampal GM and connecting GM of the superior occipitofrontal fascicle, and corpus callosum.



Figure legend: Cross-trait/cross-twin correlations for GM and WM density and VIQ/PIQ in MZ and DZ twin pairs ranging from 0 to 0.5. The cross-trait/cross-twin correlations were significant for GM density with VIQ in the right parahippocampal gyrus and for WM density with PIQ in the right superior occipitofrontal fascicle. A significant cross-trait/cross-twin correlation indicates that the genes influencing GM and WM density partly overlap with the genes that influence VIQ/PIQ. Note that, for illustration purposes, positive cross-correlations as shown here were not thresholded for significance. By definition, the cross-correlations in voxels that were not significantly determined by genetic factors could not become significant (because both factors, i.e., GM and WM density and VIQ and PIQ measures, have to be determined by genes to allow for inferences that possible mutual genes determine that association). Negative cross-correlations (data not shown) were present, but none of these reached significance.

An Elephant "Speaks"......

I wanted to pass on this curious bit from the Oct. 6 issue of Science Magazine:

A couple of years ago, an elephant trainer at South Korea's zoo in Everland Resort outside Seoul thought he heard a human voice coming out of an elephant stall. The sounds turned out to be coming from one of his charges, Kosik.

Putting the end of his trunk into his mouth, the 15-year-old Indian elephant can say short words such as bal (foot), joa (good), and anja (sit). Elephants normally make sounds through their trunks, without using their mouths. Scientists believe that Kosik blows air out of his trunk, modifying its flow by aiming at different places in his mouth and thereby generating sounds through friction with molars, inner tusks, and tongue.

Zoo veterinarians and engineers from Soongsil University in Seoul have conducted tests with Kosik. The acoustical properties of the sounds he makes are similar to those of sounds made by his trainer, Jong Gap Kim. In effect, the scientists say, Kosik is acting like a parrot. Scientists plan to conduct further studies to find out how Kosik came to mimic his trainer. Veterinarian Yang Bum Kim says elephants, who are about as smart as human toddlers, are very group-oriented and tend to copy those closest to them, suggesting that Kosik has a strong bond with trainer Kim. Kosik's parroting is not the first case of elephant mimicry. Last year, Nature published a paper on an African elephant that made "rumbling" sounds like a truck.

Biology of emotional linkages and merging of physiologies

Daniel Goleman offers a brief essay in the science section of the Oct. 10 New York Times on the biology of healing and emotional linkages between friends or married couples. The fact that mirroring systems (the subject of several previous posts in this blog) can rapidly synchronize people's posture, vocal pacing, movement, and emotional state can turn two discrete physiologies into a connected circuit that allows the biology of one person to influence that of the other. "This radically expands the scope of biology and neuroscience from focusing on a single body or brain to looking at the interplay between two at a time. In short, my hostility bumps up your blood pressure, your nurturing love lowers mine. Potentially, we are each other’s biological enemies or allies."

"There is now no doubt that this same connectivity can offer a biologically grounded emotional solace. Physical suffering aside, a healing presence can relieve emotional suffering. A case in point is a functional magnetic resonance imaging study of women awaiting an electric shock. When the women endured their apprehension alone, activity in neural regions that incite stress hormones and anxiety was heightened. As James A. Coan reported last year in an article in Psychophysiology, when a stranger held the subject’s hand as she waited, she found little relief. When her husband held her hand, she not only felt calm, but her brain circuitry quieted, revealing the biology of emotional rescue.

...But as all too many people with severe chronic diseases know, loved ones can disappear, leaving them to bear their difficulties in lonely isolation. Social rejection activates the very zones of the brain that generate, among other things, the sting of physical pain...a hospital patient’s family and friends help just by visiting, whether or not they quite know what to say."

A striking difference in brain function in autism: Failure to deactivate.

Kennedy et al report interesting functional magnetic resonance imaging (fMRI) data on normal compared with autistic brains. From their article:

Internally directed processes, such as self-reflective thought and most higher-order social and emotional processes, consistently activate a medial cortical network involving several brain regions, namely, the medial prefrontal cortex (MPFC) and adjacent rostral anterior cingulate cortex (rACC), posterior cingulate cortex (PCC), and precuneus (PrC). Interestingly, this network is active when normal subjects are passively resting, leading many to speculate that these internally directed thoughts dominate the resting state. Self-reports from subjects while at rest further support this interpretation, wherein they typically describe "autobiographical reminiscences, either recent or ancient, consisting of familiar faces, scenes, dialogues, stories, and melodies". Conversely, activity in this midline "resting network" is reduced when subjects perform externally directed, attention-demanding, goal-oriented tasks (such as the Stroop task or math calculations), and the resulting "deactivation" of this network is thought to be an indicator of an interruption of ongoing internally directed thought processes. Thus, measuring deactivation provides a means by which rest-associated functional activity can be quantitatively examined.

Applying this approach to autism, Kennedy et al found that the autism group failed to demonstrate this deactivation effect. Furthermore, there was a strong correlation between a clinical measure of social impairment and functional activity within the ventral medial prefrontal cortex. They speculate that the lack of deactivation in the autism group is indicative of abnormal internally directed processes at rest, which may be an important contribution to the social and emotional deficits of autism.

The power of positive (and negative) thinking about aging

I wanted to pass on the graphic below, from the Thursday, Oct. 5 New York Times, taken from an article on robustness versus frailty in aging. Why do some people still run marathons at age 72 while others show 'frailty', i.e. weakness, exhaustion, weight loss, and loss of muscle mass and strength? In many cases undetected cardiovascular constrictions may be at issue. What is striking is the apparent correlation of positive attitude towards aging with staying healthy longer. This is yet another example of how anticipation can shape an actual outcome. (see the 9/11/06 post on construals and performance).


Click to enlarge picture.

On average, people who had a positive view of aging when 50 years old lived an average of 7.6 years longer than those who did not hold those views. It is, of course, hard to sort out what is cause and what is effect. Some of the people with negative attitude about aging may have intuited or know that they were not really physically well. Still it seems likely that self image and stereotypes of aging play a strong role.

From the article: "When Becca Levy, a psychologist at Yale University, began her work on stereotypes’ effects on the elderly, she was not sure that she would find anything of note. ... a method that was used to study the effects of stereotypes about race and gender. The idea is to flash provocative words too quickly for people to be aware they read them. In her first study, Dr. Levy tested the memories of 90 healthy older people. Then she flashed positive words about aging like “guidance,” “wise,” “alert,” “sage” and “learned” and tested them again. Their memories were better and they even walked faster. Next, she flashed negative words like “dementia,” “decline,” “senile,” “confused” and “decrepit.” This time, her subjects’ memories were worse, and their walking paces slowed.

Thomas Hess, a psychology professor at North Carolina State University, came to a similar conclusion about the effects of stereotypes of aging. In his studies, older people did significantly worse on memory tests if they were first told something that would bring to mind aging stereotypes. It could be as simple as saying the study was on how aging affects learning and memory. They did better on memory tests if Dr. Hess first told them something positive, like saying that there was not much of a decline in memory with age."

Clever experiment: distinction of self and other in mirroring motor neurons.

Extravagant claims have been made about systems of neurons that are active both during execution of a motion or emotion and observing others doing the same thing. (Example: Ramachandran's "Mirrors Neurons will do for psychology what DNA did for Biology."). They are suggested to be a basis of empathy and the development of language.

The fact that the brain might represent others' actions like one's own raise the issue of how we distinguish self from other. What keeps us from constantly miming the actions of others? (This happens in echopraxia, the involuntary repetition or imitation of the observed movements of others.) Schütz-Bosbach et al have done a very clever experiment to examine this by manipulating the sense of body ownership (using the “rubber-hand illusion”) to compare effects of observing actions that either were or were not illusorily attributed to the subject's own body.



"When subjects watch a rubber hand being stroked while they feel synchronous stroking of their own unseen hand, they feel that the rubber hand becomes part of their body. Identical asynchronous stroking has no effect. Thus, the sense of owning the rubber hand requires congruence of visual and tactile stimulation. The neural counterparts of this sense of ownership have been identified in premotor and sensorimotor cortices. The rubber-hand illusion therefore allows balanced comparison between the self and the other because a single stimulus (here, the hand of another person rather than a rubber hand) is either linked to the self or not depending on the pattern of previous stimulation. We used a real human hand instead of the conventional rubber hand because several studies show stronger mirroring effects for viewing a live action than for viewing artificial equivalents."

They show that observing another's actions facilitated the motor system, whereas observing identical actions, which were illusorily attributed to the subject's own body, showed the opposite pattern. Thus, motor facilitation strongly depends on the agent to whom the observed action is attributed. This result contradicts previous concepts of equivalence between one's own actions and actions of others and suggests that social differentiation, not equivalence, is characteristic of the human action system.... "This suggests that the neural mechanisms underlying action observation are intrinsically social. These mechanisms map the actions of others to corresponding actions on one's own body but do not simply represent the other agent as a derivative of, or even an equal to, the self." In contrast, there appears to be an agent-specific representation in the primary motor cortex.

Language, embodiment, and the cognitive niche

This is the title of an essay by Andy Clark in Trends in Cognitive Sciences (Vol 10, no. 8., pp. 370-374, 2006). It discusses an alternatives to the "Pure Translation" view, stemming from Fodor, that knowing a natural language is knowing how to pair its expressions with encoding in some other, more fundamental inner code ('mentalese', or the Language of Thought). Rather language is viewed as a kind of self-constructed cognitive niche, a scaffold of words that is used to loop back upon itself to build the "thinking about thinking" that may be our best candidate for a distinctively human capacity, dependent upon language for its very existence. According to this model words and structured linguistic encoding act to stabilize and discipline (or 'anchor') intrinsically fluid and context-sensitive modes of thought and reason. Words and linguistic strings are among the most powerful and basic tools that we use to discipline and stabilize dynamic processes of reason and recall. Words, rather than being cues for the retrieval of meanings from some kind of passive storage, might be thought of as sensorily encountered items that 'act directly on mental states'. As embodied agents we are able to create and maintain a wide variety of cognitively empowering, self-stimulating loops whose activity is as much as aspect of our thinking as its result.

Looking beyond the Pure Translation view, language is treated as an aspect of thought, rather than just its public reflection. We eliminate the Central Executive where all the 'real thinking' happens and replace Pure Translation with an appeal to complex, distributed coordination dynamics: a 'wordful mind' that is populated by loops without leaders, that defies any simple logic of inner versus out, or of tool versus user... a mind where words really work.

Distinct roles of anterior cingulate and prefrontal cortex in the acquisition and performance of a cognitive skill

Fincham and Anderson have examined the functional roles of two cortical regions important in learning and then carrying out a cognitive skill : one in the left anterior cingulate cortex (ACC) that seems to reflect goal-relevant control demand, and one in the left prefrontal cortex (PFC) that reflects memory retrieval demand.


Fig. 1. Axial and saggital views of a). ACC (Brodmann's area 24/32 and b.) PFC (Brodmann's area 9/46), Note that the regions are left-lateralized.

Two slow event-related brain imaging experiments were conducted, adapting a cognitive skill acquisition paradigm. The first experiment found that both left ACC and left PFC activity increased parametrically with task difficulty. Using a slight modification of the same basic paradigm, the second experiment attempted to decouple retrieval and control demands over the course of learning. Participants were imaged early in training and again several days later, after substantial additional training in the task. There was a clear dissociation between activity in the left PFC and the left ACC. Although the PFC region showed a substantial decrease in activity over the course of learning, reflecting greater ease of retrieval, the ACC showed the opposite pattern of results with significantly greater activity after training, reflecting increased control demand.

Your brain can put your body wherever it likes....

Increasingly there seems to be little point in hanging on to new age spiritual, paranormal, or esoteric fantasies about altered mental states in which we seem to leave our bodies. We're actually not going anywhere... our brains are just making it up. We can, readily alter our sense of body ownership, as in the well known "rubber hand" illusion.

A nice graphic in today's New York Times prompts me to go ahead and mention a recent report from Blanke and coworkers in Nature that I was going to pass by, because it has received wide notice in the press and other blogs. This paper adds to a growing literature whose bottom line is that perturbation of nerve firing in brain areas near where the temporal and parietal lobes meet can cause a variety of distortions of our subjective sense of our body in space. Most commonly this is felt as an "out of body experience" where we are looking at ourselves from some external perspective or experiencing a 'shadow' version of ourselves. Here is the graphic from the New York Times based on work from the Blanke laboratory:


(Click to enlarge)

Does absolute brain size matter?

In recent years it has become unfashionable to talk about absolute brain size as a measure of cognitive capacity. The common assumption is that it is only meaningful to consider brain size if body size, or some relative measure, is taken into account. The idea is that since the brain, like any other organ, scales with body size, the validity of the use of brain size as a measure of intelligence or information processing capacity rests upon the size of the brain relative to the size of the body.

A review by Marino of an article by Sherwood et al. in PNAS suggests that in ignoring absolute brain size we may have thrown out the baby with the bath water. The Sherwood paper addresses the general question of whether human brains should best be thought of as large hominoid brains, or, alternatively, as a singularly endowed product of evolution somewhat apart from the rest of primate brain evolution. They indeed find that the human frontal cortex displays a higher ratio of glia to neurons than in other primates. However, and importantly, this relative difference is predicted by the allometric scaling inherent in the enlargement of the human brain. In other words, overall or absolute brain size constitutes a key factor in the ratio of glia to neurons. The authors suggest that the greater numbers of glia in the human neocortex may be due to the increased energetic costs of larger dendritic arbors and longer fiber projections within the context of the large human brain. The bottom line is that the human brain conforms to the general mammalian pattern of higher glia–neuron ratios with larger brains.

In brain areas key to specific human abilities, such as area 44( language production) and area 32 (theory-of-mind tasks in humans) Sherwood et al. find no significant species differences and suggest that the energetics of frontal cortex, even in these regions, have been largely conserved over the past 25 million years of primate brain evolution. Their overall conclusion is striking: "... human cognitive and linguistic specializations have emerged by elaborating on higher-order executive functions of the prefrontal cortex ... that evolved earlier in the primate lineage".

The fundamental insight supported by Sherwood et al. is that the human brain is not unique or anomalous, rather it is a product of changes in brain anatomy that are well predicted by scaling expectations for any nonhuman anthropoid primate. There is a growing body of evidence for this conclusion. For instance, several studies have shown that the human frontal cortex occupies the same proportion of total cortex in humans as it does in great apes. Similarly, the human brain possesses the degree of cortical gyrification expected for a primate of our brain size.

While this may be the emerging consensus there is also evidence from MRI scans of 11 different primate species that reach opposite conclusions, namely that: (1) that the human neocortex is significantly larger than expected for a primate of our brain size, (2) that the human prefrontal cortex is significantly more convoluted than expected for our brain size, and (3) that increases in cerebral white matter volume outpace increases in neocortical gray matter volume among anthropoid primates. (see Rilling and Insel, "The primate neocortex in comparative perspective using magnetic resonance imaging." Journal of Human Evolution Volume 37, Issue 2 , August 1999, Pages 191-223.)

Recollection, familiarity, and novelty in different areas of medial temporal lobes.

Daselaar et. al. have used MRI to observe memory retrieval accompanied by specific contextual details (recollection) or on the feeling that an item is old (familiarity) or new (novelty) in the absence of contextual details. There have been indications that recollection, familiarity, and novelty involve different medial temporal lobe subregions, but available evidence is scarce and inconclusive. Within the medial temporal lobes (MTLs), they found a triple dissociation among the posterior half of the hippocampus, which was associated with recollection, the posterior parahippocampal gyrus, which was associated with familiarity, and anterior half of the hippocampus and rhinal regions, which were associated with novelty. Furthermore, multiple regression analyses based on individual trial activity showed that all three memory signals, i.e., recollection, familiarity, and novelty, make significant and independent contributions to recognition memory performance.


FIG. 1. A triple dissociation within the medial temporal lobe (MTL) regarding recollection, familiarity, and novelty.

Functional dissociations among recollection, familiarity, and novelty were also found in posterior midline, left parietal cortex, and prefrontal cortex regions.


FIG. 2. Brain regions outside MTL showing recollection-, familiarity, and novelty-related activity.

There has been debate in the behavioral memory literature over whether recollection and familiarity/novelty processes are independent, given reports of correlations between behavioral measures of recollection and familiarity. The anatomical dissociations shown by the present fMRI evidence fit better with the assumption of independence.

Sex and Death in Suicide Attackers

I'm passing on verbatim this brief review from a recent issue of Science on sex differences in the motivation of suicide bombers:

"The motivations of suicide bombers differ depending on their sex, says a researcher at the University of Virginia, Charlottesville. Psychiatrist J. Anderson Thomson Jr. says that whereas males see themselves as part of a larger entity, females seem more propelled by individual motives."


"Male suicide attackers are not lone losers but members of tightly knit bands bound by ties of rage and religion. Their behavior is consistent with our ancient history of "male-bonded coalitionary violence," involving "lethal raids" practiced by small bands against their enemies, argues Thomson. But women do not fit this pattern. In a paper delivered at the biennial meeting of the International Society for Human Ethology in Detroit, Michigan, last month, Thomson mentioned Chechen, Palestinian, and Hindu female suicide terrorists who had been shunned for adultery or because they had been raped, divorced because of infertility, or whose husbands or brothers had been murdered by the enemy. In these cases, he asserts, the motives have more to do with shame or personal revenge than a larger cause. And rather than being motivated by bonds with their fellows, Thompson added, all these women were "recruited, trained, directed, or in some manner controlled by men." Brian Jenkins, a longtime terrorism expert at the RAND Corp. in Santa Monica, California, says that although the paper offers only anecdotal evidence, it contains "some interesting insights. … There clearly is a sex difference." "

Brain correlates of hysteria.

The Tuesday Science section of the New York Times (Sept 26) has an interesting article on hysteria, a fashionable syndrome in the Victorian era which has "disappeared" during this century. Actually the term "conversion disorder" is now used to describe an ill-defined syndrome with no obvious physical cause, usually involving paralysis of a portion of the body or seizures. Sigmund Freud suggested from his case studies that hysteria is something in the psyche or the mind being expressed physically in the body.


The 19th-century French neurologist Jean-Martin Charcot, shown lecturing on hysteria

Peter W. Halligan at Cardiff, co-founder of the journal Cognitive Neuropsychiatry and his colleagues "analyzed the brain function of a woman who was paralyzed on the left side of her body (Cognition, 64, B1-B8, 1997). First they conducted numerous tests to ensure that she had no identifiable organic lesion...When the woman tried to move her “paralyzed leg,” her primary motor cortex was not activated as it should have been; instead her right orbitofrontal and right anterior cingulate cortex, parts of the brain that have been associated with action and emotion, were activated. They reasoned that these emotional areas of the brain were responsible for suppressing movement in her paralyzed leg."






Fig. 1. Relative rCBF (blood flow measured by magnetic resonance imaging) increases associated with movement of the right (good) leg. The figure reveals relative rCBF increases when the normal (right) leg is moved that do not occur when attempts to move the bad (left) leg are made. There is left hemisphere neuronal activation centered on the primary sensory and motor cortex. Additional activation is seen in the left inferior parietal cortex and the right inferior temporal cortex.
Fig. 2. Relative rCBF increases associated with attempted movement of the left (bad) leg. This reveals relative rCBF increases during attempts to move the bad (left) leg that did not occur when the good (right) leg was moved. There is activation in the right anterior cingulate and the right orbito-frontal cortex.

“The patient willed her leg to move,” Dr. Halligan said. “But that act of willing triggered this primitive orbitofrontal area and activated the anterior cingulate to countermand the instruction to move the leg. She was willing it, but the leg would not move.”

"Subsequent studies have bolstered the notion that parts of the brain involved in emotion may be activated inappropriately in patients with conversion disorder and may inhibit the normal functioning of brain circuitry responsible for movement, sensation and sight......Both its persistence and its pervasiveness suggest that hysteria may be derived from an instinctual response to threat. Total shutdown, in the form of paralysis, for example, is not an entirely untoward or unheard of response to an untenable situation. (Think of deer in the headlights.)"

Analogs of human language areas in monkey brains...

A recent article in Nature Neuroscience describes how species-specific calls activate homologs of Broca's (speech generation) and Wernicke's (speech comprehension) areas in the macaque monkey. The authors identified neural systems associated with perceiving species-specific vocalizations in rhesus macaques using positron emission tomography (PET). These vocalizations evoked distinct patterns of brain activity in homologs of the human perisylvian language areas. Rather than resulting from differences in elementary acoustic properties, this activity seemed to reflect higher order auditory processing. Their finding suggests the possibility that the last common ancestor of macaques and humans, which lived 25–30 million years ago, possessed key neural mechanisms that were plausible candidates for exaptation during the evolution of language.


Figure, Broca's area of the human brain (on the right) includes Brodmann's area 44. The macaque brain (on the left, actually smaller than a human brain) has a corresponding area.