Mind-body problem

Kevin Lewis

November 25, 2012

Our fragile intellect

Gerald Crabtree
Trends in Genetics, forthcoming

Part I: New developments in genetics, anthropology, and neurobiology predict that a very large number of genes underlie our intellectual and emotional abilities, making these abilities genetically surprisingly fragile.

Part II: Analysis of human mutation rates and the number of genes required for human intellectual and emotional fitness indicates that we are almost certainly losing these abilities. If so, how did we get them in the first place, and when did things begin to change?


Metabolic constraint imposes tradeoff between body size and number of brain neurons in human evolution

Karina Fonseca-Azevedo & Suzana Herculano-Houzel
Proceedings of the National Academy of Sciences, 6 November 2012, Pages 18571-18576

Despite a general trend for larger mammals to have larger brains, humans are the primates with the largest brain and number of neurons, but not the largest body mass. Why are great apes, the largest primates, not also those endowed with the largest brains? Recently, we showed that the energetic cost of the brain is a linear function of its numbers of neurons. Here we show that metabolic limitations that result from the number of hours available for feeding and the low caloric yield of raw foods impose a tradeoff between body size and number of brain neurons, which explains the small brain size of great apes compared with their large body size. This limitation was probably overcome in Homo erectus with the shift to a cooked diet. Absent the requirement to spend most available hours of the day feeding, the combination of newly freed time and a large number of brain neurons affordable on a cooked diet may thus have been a major positive driving force to the rapid increased in brain size in human evolution.


A Knowledge-Based Theory of Rising Scores on "Culture-Free" Tests

Mark Fox & Ainsley Mitchum
Journal of Experimental Psychology: General, forthcoming

Secular gains in intelligence test scores have perplexed researchers since they were documented by Flynn (1984, 1987). Gains are most pronounced on abstract, so-called culture-free tests, prompting Flynn (2007) to attribute them to problem-solving skills availed by scientifically advanced cultures. We propose that recent-born individuals have adopted an approach to analogy that enables them to infer higher level relations requiring roles that are not intrinsic to the objects that constitute initial representations of items. This proposal is translated into item-specific predictions about differences between cohorts in pass rates and item-response patterns on the Raven's Matrices (Flynn, 1987), a seemingly culture-free test that registers the largest Flynn effect. Consistent with predictions, archival data reveal that individuals born around 1940 are less able to map objects at higher levels of relational abstraction than individuals born around 1990. Polytomous Rasch models verify predicted violations of measurement invariance, as raw scores are found to underestimate the number of analogical rules inferred by members of the earlier cohort relative to members of the later cohort who achieve the same overall score. The work provides a plausible cognitive account of the Flynn effect, furthers understanding of the cognition of matrix reasoning, and underscores the need to consider how test-takers select item responses.


Linking brains and brawn: Exercise and the evolution of human neurobiology

David Raichlen & John Polk
Proceedings of the Royal Society: Biological Sciences, 7 January 2013

The hunting and gathering lifestyle adopted by human ancestors around 2 Ma required a large increase in aerobic activity. High levels of physical activity altered the shape of the human body, enabling access to new food resources (e.g. animal protein) in a changing environment. Recent experimental work provides strong evidence that both acute bouts of exercise and long-term exercise training increase the size of brain components and improve cognitive performance in humans and other taxa. However, to date, researchers have not explored the possibility that the increases in aerobic capacity and physical activity that occurred during human evolution directly influenced the human brain. Here, we hypothesize that proximate mechanisms linking physical activity and neurobiology in living species may help to explain changes in brain size and cognitive function during human evolution. We review evidence that selection acting on endurance increased baseline neurotrophin and growth factor signalling (compounds responsible for both brain growth and for metabolic regulation during exercise) in some mammals, which in turn led to increased overall brain growth and development. This hypothesis suggests that a significant portion of human neurobiology evolved due to selection acting on features unrelated to cognitive performance.


The Relationship between Child Health, Developmental Gaps, and Parental Education: Evidence from Administrative Data

Martin Salm & Daniel Schunk
Journal of the European Economic Association, December 2012, Pages 1425-1449

We use administrative German data to examine the role of physical and mental health conditions in explaining developmental gaps between children whose parents have different educational levels. Specifically, we employ sibling fixed effect models to estimate the effect of a comprehensive list of childhood health conditions - diagnosed by government physicians - on the cognitive and verbal ability of pre-school children. We also apply decomposition methods to examine the extent to which gaps in child development can be attributed to child health conditions. While most physical health conditions have small and insignificant effects, mental health conditions, in particular hyperactivity, have a large and significant effect on development. Mental health conditions account for 14%-36% of the gap in cognitive ability and for 23%-24% of that in verbal ability. Thus, policies aimed at reducing disparities in child development and socioeconomic inequalities later in life should focus more on the early diagnosis and effective treatment of mental health conditions.


Mind-culture interactions: How writing molds mental fluidity in early development

Smaragda Kazi et al.
Intelligence, November-December 2012, Pages 622-637

This study investigated intellectual development in 4-7 years old Greek and Chinese children. They were examined on speeded performance, working memory, reasoning, and self-awareness tasks in order to investigate possible effects of learning the Chinese logographic system on possible differences in intellectual development between these ethnic groups. Speeded performance was examined with commonly familiar objects and tasks related to reading (i.e., Latin, Arabic, and Chinese characters). Chinese outperformed Greeks in (1) reading-related processing efficiency tasks but not in common objects (2) spatial but not verbal WM, (3) cognitive, and (4) the self-awareness tasks. Structural equation modeling showed that performance is organized in four systems (i.e., domain-specific problem solving, representational capacity, inference, and consciousness) integrated by g, in both ethnic groups. There were differences between the two ethnicities in the strength of relations between constructs, attributed to Chinese logographic experience. That is, the massive practice in visuo/spatial processing and memory seemed to provide an advantage in the communication between systems of the mind causing increased general cognitive fluidity, expressed in higher intellectual performance among the Chinese.


Effects of video game playing on cerebral blood flow in young adults: A SPECT study

Yuan-Hwa Chou et al.
Psychiatry Research: Neuroimaging, forthcoming

To study the impact of video game playing on the human brain, the effects of two video games playing on cerebral blood flow (CBF) in young adults were determined. Thirty healthy subjects comprising 18 males and 12 females who were familiar with video game playing were recruited. Each subject underwent three sessions of single photon emission computed tomography (SPECT) with a bolus injection of 20 mCi 99mTc ECD IV to measure their CBF. The first measurement was performed as baseline, the second and third measurements were performed after playing two different video games for 30 min, respectively. Statistic parametric mapping (SPM2) with Matlab 6.5 implemented on a personal computer was used for image analysis. CBF was significantly decreased in the prefrontal cortex and significantly increased in the temporal and occipital cortices after both video games playing. Furthermore, decreased CBF in the anterior cingulate cortex (ACC) which was significantly correlated with the number of killed characters was found after the violent game playing. The major finding of hypo-perfusion in prefrontal regions after video game playing is consistent with a previous study showing reduced or abnormal prefrontal cortex functions after video game playing. The second finding of decreased CBF in the ACC after playing the violent video game provides support for a previous hypothesis that the ACC might play a role in regulating violent behavior.


Long-term influence of normal variation in neonatal characteristics on human brain development

Kristine Walhovd et al.
Proceedings of the National Academy of Sciences, forthcoming

It is now recognized that a number of cognitive, behavioral, and mental health outcomes across the lifespan can be traced to fetal development. Although the direct mediation is unknown, the substantial variance in fetal growth, most commonly indexed by birth weight, may affect lifespan brain development. We investigated effects of normal variance in birth weight on MRI-derived measures of brain development in 628 healthy children, adolescents, and young adults in the large-scale multicenter Pediatric Imaging, Neurocognition, and Genetics study. This heterogeneous sample was recruited through geographically dispersed sites in the United States. The influence of birth weight on cortical thickness, surface area, and striatal and total brain volumes was investigated, controlling for variance in age, sex, household income, and genetic ancestry factors. Birth weight was found to exert robust positive effects on regional cortical surface area in multiple regions as well as total brain and caudate volumes. These effects were continuous across birth weight ranges and ages and were not confined to subsets of the sample. The findings show that (i) aspects of later child and adolescent brain development are influenced at birth and (ii) relatively small differences in birth weight across groups and conditions typically compared in neuropsychiatric research (e.g., Attention Deficit Hyperactivity Disorder, schizophrenia, and personality disorders) may influence group differences observed in brain parameters of interest at a later stage in life. These findings should serve to increase our attention to early influences.


Hippocampal volume varies with educational attainment across the life-span

Kimberly Noble et al.
Frontiers in Human Neuroscience, November 2012

Socioeconomic disparities - and particularly differences in educational attainment - are associated with remarkable differences in cognition and behavior across the life-span. Decreased educational attainment has been linked to increased exposure to life stressors, which in turn have been associated with structural differences in the hippocampus and the amygdala. However, the degree to which educational attainment is directly associated with anatomical differences in these structures remains unclear. Recent studies in children have found socioeconomic differences in regional brain volume in the hippocampus and amygdala across childhood and adolescence. Here we expand on this work, by investigating whether disparities in hippocampal and amygdala volume persist across the life-span. In a sample of 275 individuals from the BRAINnet Foundation database ranging in age from 17 to 87, we found that socioeconomic status (SES), as operationalized by years of educational attainment, moderates the effect of age on hippocampal volume. Specifically, hippocampal volume tended to markedly decrease with age among less educated individuals, whereas age-related reductions in hippocampal volume were less pronounced among more highly educated individuals. No such effects were found for amygdala volume. Possible mechanisms by which education may buffer age-related effects on hippocampal volume are discussed.


Secular trends in cognitive test performance: Swedish conscript data 1970-1993

Michael Rönnlund et al.
Intelligence, January-February 2013, Pages 19-24

We investigated time-related patterns in levels of cognitive performance during the period from 1970 to 1993 based on data from Swedish draft boards. The conscripts, including more than a million 18-19-year old men, had taken one of two versions of the Swedish enlistment battery (SEB67; 1970-1979 or SEB80; 1980-1993), each composed of four subtests. The results revealed significant Flynn effects, with estimated gains of 1.2-1.5 IQ-units per decade. The effect seem to hold across ability levels, even though tendencies of more pronounced effects in the lower half of the ability distribution was observed. The largest gains were for visuospatial tests (Paper Form Board and Metal Folding), with little change, even slight losses during the second sub-period, for tests of verbal knowledge (Concept Discrimination and Synonyms) and a mixed pattern for a test of technical comprehension (losses followed by gains). Finally, comparisons of trends in cognitive performance and in standing height show that the gains in cognitive performance over the years from 1980 to 1993 occurred in the absence of overall gains in height, which speaks against nutrition as the cause of the Flynn effects.


Individual differences in left parietal white matter predict math scores on the Preliminary Scholastic Aptitude Test

Anna Matejko et al.
NeuroImage, forthcoming

Mathematical skills are of critical importance, both academically and in everyday life. Neuroimaging research has primarily focused on the relationship between mathematical skills and functional brain activity. Comparatively few studies have examined which white matter regions support mathematical abilities. The current study uses diffusion tensor imaging (DTI) to test whether individual differences in white matter predict performance on the math subtest of the preliminary Scholastic Aptitude Test (PSAT). Grade 10 and 11 PSAT scores were obtained from 30 young adults (ages 17-18) with wide-ranging math achievement levels. Tract based spatial statistics was used to examine the correlation between PSAT math scores, fractional anisotropy (FA), radial diffusivity (RD) and axial diffusivity (AD). FA in left parietal white matter was positively correlated with math PSAT scores (specifically in the left superior longitudinal fasciculus, left superior corona radiata, and left corticospinal tract) after controlling for chronological age and same grade PSAT critical reading scores. Furthermore, RD, but not AD, was correlated with PSAT math scores in these white matter microstructures. The negative correlation with RD further suggests that participants with higher PSAT math scores have greater white matter integrity in this region. Individual differences in FA and RD may reflect variability in experience dependent plasticity over the course of learning and development. These results are the first to demonstrate that individual differences in white matter are associated with mathematical abilities on a nationally administered scholastic aptitude measure.


Development of white matter and reading skills

Jason Yeatman et al.
Proceedings of the National Academy of Sciences, 30 October 2012, Pages E3045-E3053

White matter tissue properties are highly correlated with reading proficiency; we would like to have a model that relates the dynamics of an individual's white matter development to their acquisition of skilled reading. The development of cerebral white matter involves multiple biological processes, and the balance between these processes differs between individuals. Cross-sectional measures of white matter mask the interplay between these processes and their connection to an individual's cognitive development. Hence, we performed a longitudinal study to measure white-matter development (diffusion-weighted imaging) and reading development (behavioral testing) in individual children (age 7-15 y). The pattern of white-matter development differed significantly among children. In the left arcuate and left inferior longitudinal fasciculus, children with above-average reading skills initially had low fractional anisotropy (FA) that increased over the 3-y period, whereas children with below-average reading skills had higher initial FA that declined over time. We describe a dual-process model of white matter development comprising biological processes with opposing effects on FA, such as axonal myelination and pruning, to explain the pattern of results.


Human-Specific Histone Methylation Signatures at Transcription Start Sites in Prefrontal Neurons

Hennady Shulha et al.
PLoS Biology, November 2012

Primate and human genomes comprise billions of base pairs, but we are unlikely to gain a deeper understanding of brain functions unique to humans (including cognitive abilities and psychiatric diseases) merely by comparing linear DNA sequences. Such determinants of species-specific function might instead be found in the so-called "epigenetic" characteristics of genomic regions; differences in the protein-packaged chromatin state in which genomic DNA exists in the cell. Here, we examine neurons from the prefrontal cortex, a brain region closely associated with the evolution of the primate brain, and identify hundreds of short DNA sequences defined by human-specific changes in chromatin structure and function when compared to non-human primates. These changes included species-specific regulation of methylation marks on the histone proteins around which genomic DNA is wrapped. Sequences subject to human-specific epigenetic regulation showed significant spatial clustering, and despite being separated by hundreds of thousands of base pairs on the linear genome, were in direct physical contact with each other through chromosomal looping and other higher order chromatin features. This observation raises the intriguing possibility that coordinated epigenetic regulation via newly derived chromatin features at gene transcription start sites could play an important role in the emergence of human-specific gene expression networks in the brain. Finally, we identified a strong genetic footprint of hominid evolution in a small subset of transcription start sites defined by human-specific gains in histone methylation, with particularly strong enrichment in prefrontal cortex neurons. For example, the base pair sequence of DPP10 (a gene critically important for normal human brain development) not only showed distinct human-specific changes, but also evidence for more recent selective pressures within the human population.


Social Rewards Enhance Offline Improvements in Motor Skill

Sho Sugawara et al.
PLoS ONE, November 2012

Motor skill memory is first encoded online in a fragile form during practice and then converted into a stable form by offline consolidation, which is the behavioral stage critical for successful learning. Praise, a social reward, is thought to boost motor skill learning by increasing motivation, which leads to increased practice. However, the effect of praise on consolidation is unknown. Here, we tested the hypothesis that praise following motor training directly facilitates skill consolidation. Forty-eight healthy participants were trained on a sequential finger-tapping task. Immediately after training, participants were divided into three groups according to whether they received praise for their own training performance, praise for another participant's performance, or no praise. Participants who received praise for their own performance showed a significantly higher rate of offline improvement relative to other participants when performing a surprise recall test of the learned sequence. On the other hand, the average performance of the novel sequence and randomly-ordered tapping did not differ between the three experimental groups. These results are the first to indicate that praise-related improvements in motor skill memory are not due to a feedback-incentive mechanism, but instead involve direct effects on the offline consolidation process.

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