Neuroimaging studies examining the effects of aging and neuropsychiatric disorders on the cerebral cortex have largely been based on measures of cortical volume. Given that cortical volume is a product of thickness and surface area, it is plausible that measures of volume capture at least 2 distinct sets of genetic influences. The present study aims to examine the genetic relationships between measures of cortical surface area and thickness. Participants were men in the Vietnam Era Twin Study of Aging (110 monozygotic pairs and 92 dizygotic pairs). Mean age was 55.8 years (range: 51-59). Bivariate twin analyses were utilized in order to estimate the heritability of cortical surface area and thickness, as well as their degree of genetic overlap. Total cortical surface area and average cortical thickness were both highly heritable (0.89 and 0.81, respectively) but were essentially unrelated genetically (genetic correlation = 0.08). This pattern was similar at the lobar and regional levels of analysis. These results demonstrate that cortical volume measures combine at least 2 distinct sources of genetic influences. We conclude that using volume in a genetically informative study, or as an endophenotype for a disorder, may confound the underlying genetic architecture of brain structure.
Surface area of the cerebral cortex is a highly heritable trait, yet little is known about genetic influences on regional cortical differentiation in humans. Using a data-driven, fuzzy clustering technique with magnetic resonance imaging data from 406 twins, we parceled cortical surface area into genetic subdivisions, creating a human brain atlas based solely on genetically informative data. Boundaries of the genetic divisions corresponded largely to meaningful structural and functional regions; however, the divisions represented previously undescribed phenotypes different from conventional (non–genetically based) parcellation systems. The genetic organization of cortical area was hierarchical, modular, and predominantly bilaterally symmetric across hemispheres. We also found that the results were consistent with human-specific regions being subdivisions of previously described, genetically based lobar regionalization patterns.
The impact of genetic and environmental factors on human brain structure is of great importance for understanding normative cognitive and brain aging as well as neuropsychiatric disorders. However, most studies of genetic and environmental influences on human brain structure have either focused on global measures or have had samples that were too small for reliable estimates. Using the classical twin design, we assessed genetic, shared environmental, and individualspecific environmental influences on individual differences in the size of 96 brain regions of interest (ROIs). Participants were 474 middle-aged male twins (202 pairs; 70 unpaired) in the Vietnam Era Twin Study (VETSA). They were 51-59 years old, and were similar to U.S. men in their age range in terms of sociodemographic and health characteristics. We measured thickness of cortical ROIs and volume of other ROIs. On average, genetic influences accounted for © 2009 Elsevier Inc. All rights reserved.Correspondence to: William S. Kremen, Ph.D., Department of Psychiatry, University of California, San Diego, 9500 Gilman Drive (MC 0738), La Jolla, CA 92093 Tel: 858-822-2393 Fax: 858-822-5856 wkremen@ucsd.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptNeuroimage. Author manuscript; available in PMC 2012 July 16. Elucidating the extent to which genetic and environmental factors influence adult brain structure is of great importance for understanding age-related normal and pathological changes in brain and cognition. Twin studies provide the optimal behavioral genetic method for clarifying this issue because they make it possible to decompose the variance of any variable into genetic, shared environmental influences, and individual-specific environmental influences. The twin method also complements molecular genetic approaches in that heritability-the proportion of phenotypic variance due to genes-is a key component for selection of phenotypes.Despite many published magnetic resonance imaging (MRI) studies involving twins (reviewed by Glahn et al., 2007;Peper et al., 2007;Schmitt et al., 2007a), the picture regarding the heritability of specific brain regions remains incomplete. In some studies, samples sizes were quite small and are thus likely to provide unstable estimates (Visscher, 2004). With a couple of exceptions, relatively few specific regions of interest (ROIs) have been examined. The different ROIs that have been measured in previous studies have often been examined in different samples. It would be advantageous to be able to compare heritabilities of differen...
Compound adhesives made from red ochre mixed with plant gum were used in the Middle Stone Age (MSA), South Africa. Replications reported here suggest that early artisans did not merely color their glues red; they deliberately effected physical transformations involving chemical changes from acidic to less acidic pH, dehydration of the adhesive near wood fires, and changes to mechanical workability and electrostatic forces. Some of the steps required for making compound adhesive seem impossible without multitasking and abstract thought. This ability suggests overlap between the cognitive abilities of modern people and people in the MSA. Our multidisciplinary analysis provides a new way to recognize complex cognition in the MSA without necessarily invoking the concept of symbolism.ochre ͉ replications ͉ glue ͉ modern behavior ͉ Ͼ70,000 years ago A rchaeologists often use symbolic material culture as a marker of modern behavior, but few agree on definitions of either term or explore the types of mental architecture required for symbolic innovations. Here, we move away from the contentious issue of symbolism and draw on the combined expertise of cognitive and earth scientists to create a fresh way of recognizing, in the deep past, cognitive abilities that overlap with our own. People today have a capacity for novel, sustained multilevel operations; this ability may have arisen from neural connectivity in part of the prefrontal cortex (1). The capacity may be recognizable in some technologies, and we use compound adhesive manufacture as our example. To demonstrate complex cognition, we must show that some executive steps required for compound adhesive manufacture are not possible without mental abilities of the kind implied in the ninth subsystem of the Barnard et al. (2) model of mental architecture. Here, abstract meanings and sophisticated organization of action sequences determine decision making. An earlier eighth subsystem would have been mentally incapable of processing 2 levels of meaning simultaneously or of generating fully abstract concepts about behavior.The use of simple (1-component) adhesives is ancient; for example, birch-bark tar was found on 2 flakes from Ϸ200,000 years (200 ka) ago at a site in Italy (3). At Ϸ40 ka, bitumen was found on stone tools in Syria (4), and a similarly aged site in Kenya yielded tools with red ochre stains that imply the use of multicomponent glue (5). Traces of even earlier (Ϸ70 ka) compound adhesives occur, together with microfractures consistent with hafting, on Middle Stone Age (MSA) stone tools from Sibudu Cave, South Africa (see SI Text and Table S1). Several recipes are evident: sometimes plant gum and red ochre (natural iron oxide-hematite-Fe 2 O 3 ) traces (Fig. 1) occur on tool portions that were once inserted in hafts (6-10). Other tools have brown plant gums and black or white fat, but no ochre ( Fig. 1 and SI Text).We acknowledge the possibility that people at Sibudu colored some of their weapons symbolically, perhaps to signify the blood of prey, but we do n...
Chromosome 6 is a metacentric chromosome that constitutes about 6% of the human genome. The finished sequence comprises 166,880,988 base pairs, representing the largest chromosome sequenced so far. The entire sequence has been subjected to high-quality manual annotation, resulting in the evidence-supported identification of 1,557 genes and 633 pseudogenes. Here we report that at least 96% of the protein-coding genes have been identified, as assessed by multi-species comparative sequence analysis, and provide evidence for the presence of further, otherwise unsupported exons/genes. Among these are genes directly implicated in cancer, schizophrenia, autoimmunity and many other diseases. Chromosome 6 harbours the largest transfer RNA gene cluster in the genome; we show that this cluster co-localizes with a region of high transcriptional activity. Within the essential immune loci of the major histocompatibility complex, we find HLA-B to be the most polymorphic gene on chromosome 6 and in the human genome.
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