Thought Provoking

Kevin Lewis

December 15, 2009

Prejudice and truth about the effect of testosterone on human bargaining behaviour

C. Eisenegger, M. Naef, R. Snozzi, M. Heinrichs & E. Fehr
Nature, forthcoming

Both biosociological and psychological models, as well as animal research, suggest that testosterone has a key role in social interactions. Evidence from animal studies in rodents shows that testosterone causes aggressive behaviour towards conspecifics. Folk wisdom generalizes and adapts these findings to humans, suggesting that testosterone induces antisocial, egoistic, or even aggressive human behaviours. However, many researchers have questioned this folk hypothesis, arguing that testosterone is primarily involved in status-related behaviours in challenging social interactions, but causal evidence that discriminates between these views is sparse. Here we show that the sublingual administration of a single dose of testosterone in women causes a substantial increase in fair bargaining behaviour, thereby reducing bargaining conflicts and increasing the efficiency of social interactions. However, subjects who believed that they received testosterone - regardless of whether they actually received it or not - behaved much more unfairly than those who believed that they were treated with placebo. Thus, the folk hypothesis seems to generate a strong negative association between subjects' beliefs and the fairness of their offers, even though testosterone administration actually causes a substantial increase in the frequency of fair bargaining offers in our experiment.


Testosterone, Facial Symmetry and Cooperation in the Prisoners' Dilemma

Santiago Sanchez-Pages & Enrique Turiegano
Physiology & Behavior, forthcoming

Recent research has analyzed how individual characteristics, like the exposure to different hormones and symmetry, affect decision-making and strategic behaviour. The present article investigates the effect of symmetry, of exposure to testosterone (T) in utero and during puberty and of current T on cooperation in a Prisoners' Dilemma Game (PDG). T is a hormone with well known effect on males' behaviour, and that promotes activities that seek to increase reproductive success. Fluctuating Asymmetry (FA) reflects the ability of the organism to maintain a stable development and it is usually employed as a variable reflecting genetic quality (low FA values are thought to signal higher genetic quality). Our results show that subjects with intermediate levels of second to fourth digit ratio (a proxy of exposure to T in utero) and with high FA cooperate more often in the PDG. We also observe that the latter effect is due to the fact that FA has an impact on subjects' expectations about the behaviour of their counterpart in the game. These results reinforce the described link between markers related to genetic quality and cooperative behaviour. This possible linkage of individual condition and pro-social behaviour in humans clearly merits further attention.


Three Randomized Controlled Trials of Early Long-Chain Polyunsaturated Fatty Acid Supplementation on Means-End Problem Solving in 9-Month-Olds

James Drover, Dennis Hoffman, Yolanda Castañeda, Sarah Morale & Eileen Birch
Child Development, September/October 2009, Pages 1376-1384

This study examines whether feeding infants formula supplemented with long-chain polyunsaturated fatty acids (LCPUFA) improves cognitive function of 9-month-olds. Participants included 229 infants from 3 randomized controlled trials. Children received either formula supplemented with docosahexaenoic acid and arachidonic acid, or a control formula beginning at 1-5 days (12-month feeding study), or following 6 weeks (6-week-weaning study) or 4-6 months of breastfeeding (4-to 6-month weaning study). Infants were assessed with a 2-step problem solving task. In the 12-month feeding and 6-week weaning studies, supplemented children had more intentional solutions (successful task completions) and higher intention scores (goal-directed behaviors) than controls. These results suggest that LCPUFA supplementation improves means-end problem solving.


The CHRNA6 Gene, Patience, and Voter Turnout

Christopher Dawes & Peter John Loewen
University of California Working Paper, October 2009

Political scientists have recently explored the genetic basis of political participation. Fowler, Baker & Dawes (2008) recently showed in two independent samples of twins that voter turnout is heritable and Fowler & Dawes (2008) identified two specific genes associated with turnout. Earlier work (Fowler & Kam 2006) has demonstrated a link between patience and turnout. We combine these insights by investigating two genes that are associated with patience and may explain variation in voter turnout. Using data from the National Longitudinal Study of Adolescent Health, we show that individuals with a version of the CHRNA6 gene are significantly less likely to have voted in the 2000 presidential election. We hypothesize that the association between the CHRNA6 gene and voting is mediated by patience.


Oxytocin receptor genetic variation relates to empathy and stress reactivity in humans

Sarina Rodrigues, Laura Saslow, Natalia Garcia, Oliver John & Dacher Keltner
Proceedings of the National Academy of Sciences, forthcoming

Oxytocin, a peptide that functions as both a hormone and neurotransmitter, has broad influences on social and emotional processing throughout the body and the brain. In this study, we tested how a polymorphism (rs53576) of the oxytocin receptor relates to two key social processes related to oxytocin: empathy and stress reactivity. Compared with individuals homozygous for the G allele of rs53576 (GG), individuals with one or two copies of the A allele (AG/AA) exhibited lower behavioral and dispositional empathy, as measured by the "Reading the Mind in the Eyes" Test and an other-oriented empathy scale. Furthermore, AA/AG individuals displayed higher physiological and dispositional stress reactivity than GG individuals, as determined by heart rate response during a startle anticipation task and an affective reactivity scale. Our results provide evidence of how a naturally occurring genetic variation of the oxytocin receptor relates to both empathy and stress profiles.


High pregnancy anxiety during mid-gestation is associated with decreased gray matter density in 6-9-year-old children

Claudia Buss, Elysia Poggi Davis, Tugan Muftuler, Kevin Head & Curt Sandman
Psychoneuroendocrinology, January 2010, Pages 141-153

Because the brain undergoes dramatic changes during fetal development it is vulnerable to environmental insults. There is evidence that maternal stress and anxiety during pregnancy influences birth outcome but there are no studies that have evaluated the influence of stress during human pregnancy on brain morphology. In the current prospective longitudinal study we included 35 women for whom serial data on pregnancy anxiety was available at 19 (±0.83), 25 (±0.9) and 31 (±0.9) weeks gestation. When the offspring from the target pregnancy were between 6 and 9 years of age, their neurodevelopmental stage was assessed by a structural MRI scan. With the application of voxel-based morphometry, we found regional reductions in gray matter density in association with pregnancy anxiety after controlling for total gray matter volume, age, gestational age at birth, handedness and postpartum perceived stress. Specifically, independent of postnatal stress, pregnancy anxiety at 19 weeks gestation was associated with gray matter volume reductions in the prefrontal cortex, the premotor cortex, the medial temporal lobe, the lateral temporal cortex, the postcentral gyrus as well as the cerebellum extending to the middle occipital gyrus and the fusiform gyrus. High pregnancy anxiety at 25 and 31 weeks gestation was not significantly associated with local reductions in gray matter volume.This is the first prospective study to show that a specific temporal pattern of pregnancy anxiety is related to specific changes in brain morphology. Altered gray matter volume in brain regions affected by prenatal maternal anxiety may render the developing individual more vulnerable to neurodevelopmental and psychiatric disorders as well as cognitive and intellectual impairment.


Timing and Trajectories of Fetal Growth Related to Cognitive Development in Childhood

Ondine von Ehrenstein, Rafael Mikolajczyk & Jun Zhang
American Journal of Epidemiology, 1 December 2009, Pages 1388-1395

The authors investigated timing and trajectories of fetal growth in relation to childhood development in the National Institute of Child Health and Human Development-Scandinavian Study of Successive Small-for-Gestational Age Births (1986-1988) (n = 1,059). Fetal size was assessed by ultrasound at 17, 25, and 33 gestational weeks and at birth. Bayley Scales of Infant Development and the Wechsler Preschool and Primary Scale of Intelligence-Revised tests were conducted at ages 1 and 5 years, respectively, producing mental and psychomotor development indexes and verbal and performance intelligence quotients. Relative fetal size was calculated as a standard deviation score at each data point; growth trajectories were explored with longitudinal mixture models. Fetal size at 17, 25, and 33 weeks was positively associated with mental development index; larger size at 33 weeks and at birth was associated with higher verbal intelligence quotient scores (2.61, 95% confidence interval: 1.06, 4.15 and 1.90, 95% confidence interval: 0.67, 3.13 increase per 1 standard deviation score, respectively); findings were similar for performance intelligence quotient. Seven trajectories were identified; scores were lower for "small" and "medium-to-small" trajectories than for "medium" and "big" (representing normal size) trajectories: mental development index (P < 0.01), performance intelligence quotient (P < 0.001), and verbal intelligence quotient (P < 0.001). Overall, larger fetal size in the second and third trimesters was positively associated with childhood development. Fetal growth trajectories may matter beyond birth.


Caffeine Consumption and Cognitive Function at Age 70: The Lothian Birth Cohort 1936 Study

Janie Corley, Xueli Jia, Janet Kyle, Alan Gow, Caroline Brett, John Starr, Geraldine McNeill & Ian Deary
Psychosomatic Medicine, forthcoming

Objective: To investigate the association between caffeine consumption and cognitive outcomes in later life.

Methods: Participants were 923 healthy adults from the Lothian Birth Cohort 1936 Study, on whom there were intelligence quotient (IQ) data from age 11 years. Cognitive function at age 70 years was assessed, using tests measuring general cognitive ability, speed of information processing, and memory. Current caffeine consumption (using multiple measures of tea, coffee, and total dietary caffeine) was obtained by self-report questionnaire, and demographic and health information was collected in a standardized interview.

Results: In age- and sex-adjusted models, there were significant positive associations between total caffeine intake and general cognitive ability and memory. After adjustment for age 11 IQ and social class, both individually and together, most of these associations became nonsignificant. A robust positive association, however, was found between drinking ground coffee (e.g., filter and espresso) and performance on the National Adult Reading Test (NART, p = .007), and the Wechsler Test of Adult Reading (WTAR, p = .02). No gender effects were observed, contrary to previous studies. Generally, higher cognitive scores were associated with coffee consumption, and lower cognitive scores with tea consumption, but these effects were not significant in the fully adjusted model.

Conclusions: The present study is rare in having childhood IQ in a large sample of older people. The results suggest that the significant caffeine intake-cognitive ability associations are bidirectional-because childhood IQ and estimated prior IQ are associated with the type of caffeine intake in old age-and partly confounded by social class.


Tobacco smoking produces widespread dominant brain wave alpha frequency increases

Edward Domino, Lisong Ni, Michael Thompson, Huilei Zhang, Hiroki Shikata, Hiromi Fukai, Takeshi Sakaki & Ippei Ohya
International Journal of Psychophysiology, December 2009, Pages 192-198

The major pharmacological ingredient in tobacco smoke is nicotine, a mild stimulant known to alter brain electrical activity. The objective of this study was to determine if tobacco smoking in humans produces localized or widespread neocortical dominant alpha electroencephalographic (EEG) frequency increases consistent with nicotine stimulation of the brainstem activating system in animals. Twenty-two male volunteer non-deprived tobacco smokers were studied. They were asked not to smoke for at least 1 h before the experiment in mid-morning as part of their usual smoking schedule. In the laboratory, they sham smoked and then smoked their favorite tobacco cigarette. Two experimental sessions (#1 and #2) were conducted, separated by a one to two month interval. In both sessions, there were minor statistically significant increases in the dominant alpha frequencies after sham smoking. In both sessions, after the subjects smoked a favorite tobacco cigarette there was a significant generalized increase in dominant alpha EEG frequencies in most scalp recording sites. This study demonstrates that tobacco smoking produces widespread bilateral neocortical increases in dominant alpha EEG frequencies consistent with the stimulant effects of nicotine on the brainstem reticular activating system.


Breastfeeding, Maternal Education and Cognitive Function: A Prospective Study in Twins

M. Bartels, C. van Beijsterveldt & D. Boomsma
Behavior Genetics, November 2009, Pages 616-622

The effect of breastfeeding on cognitive abilities is examined in the offspring of highly educated women and compared to the effects in women with low or middle educational attainment. All offspring consisted of 12-year old mono- or dizygotic twins and this made it possible to study the effect of breastfeeding on mean cognition scores as well as the moderating effects of breastfeeding on the heritability of variation in cognition. Information on breastfeeding and cognitive ability was available for 6,569 children. Breastfeeding status was prospectively assessed in the first years after birth of the children. Maternal education is positively associated with performance on a standardized test for cognitive ability in offspring. A significant effect of breastfeeding on cognition was also observed. The effect was similar for offspring with mothers with a high, middle, and low educational level. Breast-fed children of highly educated mothers score on average 7.6 point higher on a standardized test of cognitive abilities (CITO test; range 500-550; effects size = .936) than formula-fed children of mothers with a low education. Individual differences in cognition scores are largely accounted for by additive genetic factors (80%) and breastfeeding does not modify the effect of genetic factors in any of the three strata of maternal education. Heritability was slightly lower in children with a mother with a middle-level education.


Cardiovascular fitness is associated with cognition in young adulthood

Maria Åberg, Nancy Pedersen, Kjell Torén, Magnus Svartengren, Björn Bäckstrand, Tommy Johnsson, Christiana Cooper-Kuhn, David Åberg, Michael Nilsson & Georg Kuhn
Proceedings of the National Academy of Sciences, 8 December 2009, Pages 20906-20911

During early adulthood, a phase in which the central nervous system displays considerable plasticity and in which important cognitive traits are shaped, the effects of exercise on cognition remain poorly understood. We performed a cohort study of all Swedish men born in 1950 through 1976 who were enlisted for military service at age 18 (N = 1,221,727). Of these, 268,496 were full-sibling pairs, 3,147 twin pairs, and 1,432 monozygotic twin pairs. Physical fitness and intelligence performance data were collected during conscription examinations and linked with other national databases for information on school achievement, socioeconomic status, and sibship. Relationships between cardiovascular fitness and intelligence at age 18 were evaluated by linear models in the total cohort and in subgroups of full-sibling pairs and twin pairs. Cardiovascular fitness, as measured by ergometer cycling, positively associated with intelligence after adjusting for relevant confounders (regression coefficient b = 0.172; 95% CI, 0.168-0.176). Similar results were obtained within monozygotic twin pairs. In contrast, muscle strength was not associated with cognitive performance. Cross-twin cross-trait analyses showed that the associations were primarily explained by individual specific, non-shared environmental influences (≥80%), whereas heritability explained <15% of covariation. Cardiovascular fitness changes between age 15 and 18 y predicted cognitive performance at 18 y. Cox proportional-hazards models showed that cardiovascular fitness at age 18 y predicted educational achievements later in life. These data substantiate that physical exercise could be an important instrument for public health initiatives to optimize educational achievements, cognitive performance, as well as disease prevention at the society level.


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