Differences In Brain Size Research Articles

Tachykinin Expression Levels Correlate with Caste-Specific Aggression in Workers of the Leaf-Cutting Ant Acromyrmex echinatior

The tachykinins are a family of neuropeptides that influence a range of behavioral phenotypes in both vertebrates and invertebrates; they appear to have a conserved role in the processing of stimuli, and in the control of aggression in a wide range of animals. Expression of tachykinin in a cluster of neurons was recently shown to determine the stimulus response threshold for aggressive behavior in Drosophila (1). Varying response thresholds are often implicated in division of labor within social insect colonies, so we hypothesized that Tachykinin could play a role in the organization of colony defense by affecting individual response thresholds to non-nestmate stimuli. We used quantitative-PCR in combination with behavioral assays to test for associations between the expression of Tachykinin and its receptor, and the aggressive division of labor among the castes of the leaf-cutting ant Acromyrmex echinatior, a species with multiple worker castes. After correction for differences in brain size among castes, we found that the most aggressive large worker caste had the highest Tachykinin expression levels, but that no such effect was apparent for breeding and virgin queens. To further evaluate these deviating results for the reproductive caste, we manipulated the aggression threshold of virgin-queens by removing their wings, which is known to make them express a soldier-like behavioral phenotype. Despite heightened aggression, expression levels of Tachykinin remained unaffected, suggesting that aggression levels in reproductive caste phenotypes are controlled by differential expression of other genes.

Effects of Habitat and Social Complexity on Brain Size, Brain Asymmetry and Dentate Gyrus Morphology in Two Octodontid Rodents

Navigational and social challenges due to habitat conditions and sociality are known to influence dentate gyrus (DG) morphology, yet the relative importance of these factors remains unclear. Thus, we studied three natural populations of O. lunatus (Los Molles) and Octodon degus (El Salitre and Rinconada), two caviomorph species that differ in the extent of sociality and with contrasting vegetation cover of habitat used. The brains and DG of male and female breeding degus with simultaneous information on their physical and social environments were examined. The extent of sociality was quantified from total group size and range area overlap. O. degus at El Salitre was more social than at Rinconada and than O. lunatus from Los Molles. The use of transects to quantify cover of vegetation (and other physical objects in the habitat) and measures of the spatial behavior of animals indicated animal navigation based on unique cues or global landmarks is more cognitively challenging to O. lunatus. During lactation, female O. lunatus had larger brains than males. Relative DG volume was similar across sexes and populations. The right hemisphere of male and female O. lunatus had more cells than the left hemisphere, with DG directional asymmetry not found in O. degus. Degu population differences in brain size and DG cell number seemed more responsive to differences in habitat than to differences in sociality. Yet, large-sized O. degus (but not O. lunatus) that ranged over larger areas and were members of larger social groups had more DG cells per hemisphere. Thus, within-population variation in DG cell number by hemisphere was consistent with a joint influence of habitat and sociality in O. degus at El Salitre.

The life-history basis of behavioural innovations.

The evolutionary origin of innovativeness remains puzzling because innovating means responding to novel or unusual problems and hence is unlikely to be selected by itself. A plausible alternative is considering innovativeness as a co-opted product of traits that have evolved for other functions yet together predispose individuals to solve problems by adopting novel behaviours. However, this raises the question of why these adaptations should evolve together in an animal. Here, we develop the argument that the adaptations enabling animals to innovate evolve together because they are jointly part of a life-history strategy for coping with environmental changes. In support of this claim, we present comparative evidence showing that in birds, (i) innovative propensity is linked to life histories that prioritize future over current reproduction, (ii) the link is in part explained by differences in brain size, and (iii) innovative propensity and life-history traits may evolve together in generalist species that frequently expose themselves to novel or unusual conditions. Combined with previous evidence, these findings suggest that innovativeness is not a specialized adaptation but more likely part of a broader general adaptive system to cope with changes in the environment.

Brain size affects the behavioural response to predators in female guppies (Poecilia reticulata).

Large brains are thought to result from selection for cognitive benefits, but how enhanced cognition leads to increased fitness remains poorly understood. One explanation is that increased cognitive ability results in improved monitoring and assessment of predator threats. Here, we use male and female guppies (Poecilia reticulata), artificially selected for large and small brain size, to provide an experimental evaluation of this hypothesis. We examined their behavioural response as singletons, pairs or shoals of four towards a model predator. Large-brained females, but not males, spent less time performing predator inspections, an inherently risky behaviour. Video analysis revealed that large-brained females were further away from the model predator when in pairs but that they habituated quickly towards the model when in shoals of four. Males stayed further away from the predator model than females but again we found no brain size effect in males. We conclude that differences in brain size affect the female predator response. Large-brained females might be able to assess risk better or need less sensory information to reach an accurate conclusion. Our results provide experimental support for the general idea that predation pressure is likely to be important for the evolution of brain size in prey species.

The evolution of face processing networks

Recent studies in marmosets, macaques, and humans have begun to show commonalities and differences in the evolution of face processing networks. Despite differences in brain size and gyrification across species, myelination and motion may be key anatomical and functional features contributing to the surprising similarity of face networks across species.

Reconstructed Homo habilis type OH 7 suggests deep-rooted species diversity in early Homo.

Besides Homo erectus (sensu lato), the eastern African fossil record of early Homo has been interpreted as representing either a single variable species, Homo habilis, or two species. In the latter case, however, there is no consensus over the respective groupings, and which of the two includes OH 7, the 1.8-million-year-old H. habilis holotype. This partial skull and hand from Olduvai Gorge remains pivotal to evaluating the early evolution of the Homo lineage, and by priority names one or other of the two taxa. However, the distorted preservation of the diagnostically important OH 7 mandible has hindered attempts to compare this specimen with other fossils. Here we present a virtual reconstruction of the OH 7 mandible, and compare it to other early Homo fossils. The reconstructed mandible is remarkably primitive, with a long and narrow dental arcade more similar to Australopithecus afarensis than to the derived parabolic arcades of Homo sapiens or H. erectus. We find that this shape variability is not consistent with a single species of early Homo. Importantly, the jaw morphology of OH 7 is incompatible with fossils assigned to Homo rudolfensis and with the A.L. 666-1 Homo maxilla. The latter is morphologically more derived than OH 7 but 500,000years older, suggesting that the H. habilis lineage originated before 2.3 million years ago, thus marking deep-rooted species diversity in the genus Homo. We also reconstructed the parietal bones of OH 7 and estimated its endocranial volume. At between 729 and 824ml it is larger than any previously published value, and emphasizes the near-complete overlap in brain size among species of early Homo. Our results clarify the H. habilis hypodigm, but raise questions about its phylogenetic relationships. Differences between species of early Homo appear to be characterized more by gnathic diversity than by differences in brain size, which was highly variable within all taxa.

Brain Geometry and its Relation to Migratory Behavior in Birds

A central concern in neuroscience can simply be brought down to the question of how a brains organization relates to its great diversity of functions. It is generally agreed that this relation must be based on multiscale organizational principles, ranging from the macroscopic level of the entire organ down to the cellular and molecular level. The functional correlates may also be seen as hierarchical constructs ranging from phylogenetic constraints and selectable life history traits down to perception, action and cognition. Here we focus on the relationship between macroscopic brain measures and a conspicuous life history variable in many animal species, migration. Migratory songbirds tend to have smaller brains than resident species. However, in the absence of data providing a detailed mapping of variation in brain subdivisions onto variation in migratory behaviour, offering a causal interpretation of the observed difference in brain size is difficult. Here we describe a set of large scale, geometric measures, which, despite different phylogenetic affiliations, discriminate migratory status across multiple avian lineages and eco-geographical regions. We build our investigation on complete, serial-section based, 3-D volumetric reconstructions of telencephalic subdivisions involving four song bird genera, which differ in their migratory status: long distance (more than 3000 km) and modest or no (0-3000 km) migratory behaviour. Our findings suggest that migratory behaviour as a population level trait can be discriminated at the level of geometrical forebrain measures. We finally discuss the results with respect to the developmental patterns that are largely responsible for the observed differences in brain geometries.

Recent Developments in Diagnosis and Care for Girls in Turner Syndrome

The past decade produced important advances in molecular genetic techniques potentially supplanting the traditional cytogenetic diagnosis of Turner syndrome (TS). Rapidly evolving genomic technology is used to screen 1st trimester pregnancies for sex chromosomal anomalies including TS, and genomic approaches are suggested for the postnatal diagnosis of TS. Understanding the interpretation and limitations of new molecular tests is essential for clinicians to provide effective counseling to parents or patients impacted by these tests. Recent studies have advanced the concept that X chromosome genomic imprinting influences expression of the Turner phenotype and contributes to gender differences in brain size and coronary disease. Progress in cardiovascular MRI over the past decade has dramatically changed our view of the scope and criticality of congenital heart disease in TS. Cardiac MRI is far more effective than transthoracic echocardiography in detecting aortic valve abnormalities, descending aortic aneurysm, and partial anomalous pulmonary venous return; recent technical advances allow adequate imaging in girls as young as seven without breath holding or sedation. Finally, important developments in the area of gynecological management of girls and young women with TS are reviewed, including prognostic factors that predict spontaneous puberty and potential fertility and recent practice guidelines aimed at reducing cardiovascular risk for oocyte donation pregnancies in TS.

The “It” Factor

The article focuses on the physiological and cognitive differences between humans and chimpanzees. Topics include how Homo sapiens became the dominant species, how human behavior differs from the behavior of apes, and the link between language and human evolution. Information is provided on the brain size differences between humans and chimpanzees.

Meta-Analysis of Associations Between Human Brain Volume And Intelligence Differences: How Strong Are They and What Do They Mean?

Positive associations between human intelligence and brain size have been suspected for more than 150 years. Nowadays, modern non-invasive measures of in vivo brain volume (Magnetic Resonance Imaging) make it possible to reliably assess associations with IQ. By means of a systematic review of published studies and unpublished results obtained by personal communications with researchers, we identified 88 studies examining effect sizes of 148 healthy and clinical mixed-sex samples (> 8,000 individuals). Our results showed significant positive associations of brain volume and IQ (r = .24, R2 = .06) that generalize over age (children vs. adults), IQ domain (full-scale, performance, and verbal IQ), sample type (clinical vs. healthy sample), and sex. Application of a number of methods for detection of publication bias indicates that strong and positive correlation coefficients have been reported frequently in the literature whilst small and non-significant associations appear to have been often omitted from reports. We show that although the positive association of brain volume and IQ seems to be robust, its strength has been overestimated in the literature. While it is tempting to interpret this association in the context of human cognitive evolution and species differences in brain size and cognitive ability, we show that it is not warranted to interpret brain size as a necessary cause or isomorphic proxy of human intelligence differences.

A tensor-based morphometry analysis of regional differences in brain volume in relation to prenatal alcohol exposure.

Reductions in brain volumes represent a neurobiological signature of fetal alcohol spectrum disorders (FASD). Less clear is how regional brain tissue reductions differ after normalizing for brain size differences linked with FASD and whether these profiles can predict the degree of prenatal exposure to alcohol. To examine associations of regional brain tissue excesses/deficits with degree of prenatal alcohol exposure and diagnosis with and without correction for overall brain volume, tensor-based morphometry (TBM) methods were applied to structural imaging data from a well-characterized, demographically homogeneous sample of children diagnosed with FASD (n = 39, 9.6–11.0 years) and controls (n = 16, 9.5–11.0 years). Degree of prenatal alcohol exposure was significantly associated with regionally pervasive brain tissue reductions in: (1) the thalamus, midbrain, and ventromedial frontal lobe, (2) the superior cerebellum and inferior occipital lobe, (3) the dorsolateral frontal cortex, and (4) the precuneus and superior parietal lobule. When overall brain size was factored out of the analysis on a subject-by-subject basis, no regions showed significant associations with alcohol exposure. FASD diagnosis was associated with a similar deformation pattern, but few of the regions survived FDR correction. In data-driven independent component analyses (ICA) regional brain tissue deformations successfully distinguished individuals based on extent of prenatal alcohol exposure and to a lesser degree, diagnosis. The greater sensitivity of the continuous measure of alcohol exposure compared with the categorical diagnosis across diverse brain regions underscores the dose dependence of these effects. The ICA results illustrate that profiles of brain tissue alterations may be a useful indicator of prenatal alcohol exposure when reliable historical data are not available and facial features are not apparent.

Why size matters: Differences in brain volume account for apparent sex differences in callosal anatomy: The sexual dimorphism of the corpus callosum

Numerous studies have demonstrated a sexual dimorphism of the human corpus callosum. However, the question remains if sex differences in brain size, which typically is larger in men than in women, or biological sex per se account for the apparent sex differences in callosal morphology. Comparing callosal dimensions between men and women matched for overall brain size may clarify the true contribution of biological sex, as any observed group difference should indicate pure sex effects. We thus examined callosal morphology in 24 male and 24 female brains carefully matched for overall size. In addition, we selected 24 extremely large male brains and 24 extremely small female brains to explore if observed sex effects might vary depending on the degree to which male and female groups differed in brain size. Using the individual T1-weighted brain images (n=96), we delineated the corpus callosum at midline and applied a well-validated surface-based mesh-modeling approach to compare callosal thickness at 100 equidistant points between groups determined by brain size and sex. The corpus callosum was always thicker in men than in women. However, this callosal sex difference was strongly determined by the cerebral sex difference overall. That is, the larger the discrepancy in brain size between men and women, the more pronounced the sex difference in callosal thickness, with hardly any callosal differences remaining between brain-size matched men and women. Altogether, these findings suggest that individual differences in brain size account for apparent sex differences in the anatomy of the corpus callosum.

Monkeys perform as well as apes and humans in a size discrimination task

Whether the cognitive competences of monkeys and apes are rather similar or whether the larger-brained apes outperform monkeys in cognitive experiments is a highly debated topic. Direct comparative analyses are therefore essential to examine similarities and differences among species. We here compared six primate species, including humans, chimpanzees, bonobos, gorillas (great apes), olive baboons, and long-tailed macaques (Old World monkeys) in a task on fine-grained size discrimination. Except for gorillas, subjects of all taxa (i.e. humans, apes, and monkeys) were able to discriminate three-dimensional cubes with a volume difference of only 10 % (i.e. cubes of 50 and 48 mm side length) and performed only slightly worse when the cubes were presented successively. The minimal size discriminated declined further with increasing time delay between presentations of the cubes, highlighting the difficulty to memorize exact size differences. The results suggest that differences in brain size, as a proxy for general cognitive abilities, did not account for variation in performance, but that differential socio-ecological pressures may better explain species differences. Our study highlights the fact that differences in cognitive abilities do not always map neatly onto phylogenetic relationships and that in a number of cognitive experiments monkeys do not fare significantly worse than apes, casting doubt on the assumption that larger brains per se confer an advantage in such kinds of tests.Electronic supplementary materialThe online version of this article (doi:10.1007/s10071-013-0616-0) contains supplementary material, which is available to authorized users.

Network efficiency in autism spectrum disorder and its relation to brain overgrowth

A substantial body of evidence links differences in brain size to differences in brain organization. We have hypothesized that the developmental aspect of this relation plays a role in autism spectrum disorder (ASD), a neurodevelopmental disorder which involves abnormalities in brain growth. Children with ASD have abnormally large brains by the second year of life, and for several years thereafter their brain size can be multiple standard deviations above the norm. The greater conduction delays and cellular costs presumably associated with the longer long-distance connections in these larger brains is thought to influence developmental processes, giving rise to an altered brain organization with less communication between spatially distant regions. This has been supported by computational models and by findings linking greater intra-cranial volume, an index of maximum brain-size during development, to reduced inter-hemispheric connectivity in individuals with ASD. In this paper, we further assess this hypothesis via a whole-brain analysis of network efficiency. We utilize diffusion tractography to estimate the strength and length of the connections between all pairs of cortical regions. We compute the efficiency of communication between each network node and all others, and within local neighborhoods; we then assess the relation of these measures to intra-cranial volume, and the differences in these measures between adults with autism and typical controls. Intra-cranial volume is shown to be inversely related to efficiency for wide-spread regions of cortex. Moreover, the spatial patterns of reductions in efficiency in autism bear a striking resemblance to the regional relationships between efficiency and intra-cranial volume, particularly for local efficiency. The results thus provide further support for the hypothesized link between brain overgrowth in children with autism and the efficiency of the organization of the brain in adults with autism.

Interspecies avian brain chimeras reveal that large brain size differences are influenced by cell-interdependent processes.

Like humans, birds that exhibit vocal learning have relatively delayed telencephalon maturation, resulting in a disproportionately smaller brain prenatally but enlarged telencephalon in adulthood relative to vocal non-learning birds. To determine if this size difference results from evolutionary changes in cell-autonomous or cell-interdependent developmental processes, we transplanted telencephala from zebra finch donors (a vocal-learning species) into Japanese quail hosts (a vocal non-learning species) during the early neural tube stage (day 2 of incubation), and harvested the chimeras at later embryonic stages (between 9–12 days of incubation). The donor and host tissues fused well with each other, with known major fiber pathways connecting the zebra finch and quail parts of the brain. However, the overall sizes of chimeric finch telencephala were larger than non-transplanted finch telencephala at the same developmental stages, even though the proportional sizes of telencephalic subregions and fiber tracts were similar to normal finches. There were no significant changes in the size of chimeric quail host midbrains, even though they were innervated by the physically smaller zebra finch brain, including the smaller retinae of the finch eyes. Chimeric zebra finch telencephala had a decreased cell density relative to normal finches. However, cell nucleus size differences between each species were maintained as in normal birds. These results suggest that telencephalic size development is partially cell-interdependent, and that the mechanisms controlling the size of different brain regions may be functionally independent.

Nuclear organization of cholinergic, putative catecholaminergic, serotonergic and orexinergic systems in the brain of the African pygmy mouse (Mus minutoides): Organizational complexity is preserved in small brains

This study investigated the nuclear organization of four immunohistochemically identifiable neural systems (cholinergic, catecholaminergic, serotonergic and orexinergic) within the brain of the African pygmy mouse (Mus minutoides). The African pygmy mice studied had a brain mass of around 275mg, making these the smallest rodent brains to date in which these neural systems have been investigated. In contrast to the assumption that in this small brain there would be fewer subdivisions of these neural systems, we found that all nuclei generally observed for these systems in other rodent brains were also present in the brain of the African pygmy mouse. As with other rodents previously studied in the subfamily Murinae, we observed the presence of cortical cholinergic neurons and a compactly organized locus coeruleus. These two features of these systems have not been observed in the non-Murinae rodents studied to date. Thus, the African pygmy mouse displays what might be considered a typical Murinae brain organization, and despite its small size, the brain does not appear to be any less complexly organized than other rodent brains, even those that are over 100 times larger such as the Cape porcupine brain. The results are consistent with the notion that changes in brain size do not affect the evolution of nuclear organization of complex neural systems. Thus, species belonging to the same order generally have the same number and complement of the subdivisions, or nuclei, of specific neural systems despite differences in brain size, phenotype or time since evolutionary divergence.

Rushton’s contributions to the study of mental ability

This essay describes Rushton’s contribution to examining the nexus of intelligence, race, and genetics, specifically what I termed “Spearman’s hypothesis”. It states that Black–White differences are “most marked in just those [tests] which are known to be saturated with g”. I (Jensen) had confirmed this hypothesis using large data sets in the 1970s and 1980s and also found that Black–White differences were most marked on the more heritable rather than the more cultural subtests. Rushton confirmed and extended these findings in many highly innovative ways and demonstrated Spearman’s hypothesis applied among samples of Gypsy Roma in Serbia, and East Asian, European, South Asian, Colored and Black samples in South Africa. He has not only documented group differences in brain size, intelligence, life span, family structure, infant mortality, developmental precocity, personality, and temperament, and rates of two egg twinning, and crime among East Asians, Europeans, and Africans, but also provided a life history theory that explains them.

In vivo vs. ex vivo Magnetic Resonance Imaging In Mice

GENERAL COMMENTARY article Front. Neuroinform., 17 May 2012 https://doi.org/10.3389/fninf.2012.00019

Age‐related changes of digital endocranial volume during human ontogeny: Results from an osteological reference collection

Endocranial volume (EV) estimation is widely used in physical anthropology for assessing brain size differences between taxa and monitoring the emergence of brain growth patterns in modern humans. However, to date, no reference data are available for modern human EV ontogeny. We measured 94 skulls with known sex and age (ranging from 0 to 7.5 years) from the osteological collection of Strasbourg University (OCSU) by using an accurate digital active contour model algorithm on 3D virtual models, reconstructed by CT. The OCSU data also allow us to propose improved equations for estimating EV in immature individuals from dry skull diameters (length, width, and height). Aside from the EV, the average proportional endocranial volume (PEV), corresponding to the ratio of EV at a given age to the average EV in the corresponding adult population, was also computed. EV nearly doubles during the first year of life, and later continues to expand more slowly, at least until 7 years of age. No sex differences can be demonstrated between the EV distributions of boys and girls in this sample. However, although PEV at birth is identical in girls and boys, it later displays significantly higher values in the girls of our series. PEV obtained at birth is 22%, which is quite different from values established for the brain itself from autopsied individuals, or MRI data. This suggests that assessments of EV and PEV values in fossil specimens should be conducted by using identical measures in comparative samples of extant humans and apes.

Brain enlargement is associated with regression in preschool-age boys with autism spectrum disorders

Autism is a heterogeneous disorder with multiple behavioral and biological phenotypes. Accelerated brain growth during early childhood is a well-established biological feature of autism. Onset pattern, i.e., early onset or regressive, is an intensely studied behavioral phenotype of autism. There is currently little known, however, about whether, or how, onset status maps onto the abnormal brain growth. We examined the relationship between total brain volume and onset status in a large sample of 2- to 4-y-old boys and girls with autism spectrum disorder (ASD) [n = 53, no regression (nREG); n = 61, regression (REG)] and a comparison group of age-matched typically developing controls (n = 66). We also examined retrospective head circumference measurements from birth through 18 mo of age. We found that abnormal brain enlargement was most commonly found in boys with regressive autism. Brain size in boys without regression did not differ from controls. Retrospective head circumference measurements indicate that head circumference in boys with regressive autism is normal at birth but diverges from the other groups around 4-6 mo of age. There were no differences in brain size in girls with autism (n = 22, ASD; n = 24, controls). These results suggest that there may be distinct neural phenotypes associated with different onsets of autism. For boys with regressive autism, divergence in brain size occurs well before loss of skills is commonly reported. Thus, rapid head growth may be a risk factor for regressive autism.