***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Publication bias , sometimes known as the " file-drawer problem " or " funnel-plot asymmetry , " is common in empirical research . The authors review the implication s of publication bias for quantitative research synthesis ( meta- analysis ) and describe existing techniques for detecting and correcting it . A new approach is proposed that is suitable for application to meta-analytic data sets that are too small for the application of existing methods . The model estimates parameters relevant to fixed-effects , mixed-effects or r and om-effects meta- analysis contingent on a hypothetical pattern of bias that is fixed independently of the data . The authors illustrate this approach for sensitivity analysis using 3 data sets adapted from a commonly cited reference work on research synthesis ( H. M. Cooper & L. V. Hedges , 1994 ) Children born preterm and of very low birth weight have an increased incidence of learning difficulties , but little is known about the specific nature of their cognitive deficits and the underlying neuropathology . We hypothesized that their vulnerability to hypoxic , metabolic , and nutritional insults would lead to reduced hippocampal volumes and to deficits in memory because of the role of the hippocampus in this domain of cognition . Neuropsychological and magnetic resonance imaging methods were used to investigate this hypothesis in adolescents born preterm ( ≤30 wk gestation , n = 11 ) or full-term ( n = 8) . The preterm group had significantly smaller hippocampal volumes bilaterally , despite equivalent head size , and showed specific deficits in certain aspects of everyday memory , both on objective testing and as indicated by parental question naires . The preterm group also had a specific deficit in numeracy . The reduced hippocampal volumes and deficits in everyday memory have previously been unrecognized , but their prevalence in a group of neurologically normal children is striking The neural basis of variation in human intelligence is not well delineated . Numerous studies relating measures of brain size such as brain weight , head circumference , CT or MRI brain volume to different intelligence test measures , with variously defined sample s of subjects have yielded inconsistent findings with correlations from approximately 0 to 0.6 , with most correlations approximately 0.3 or 0.4 . The study of intelligence in relation to postmortem cerebral volume is not available to date . We report the results of such a study on 100 cases ( 58 women and 42 men ) having prospect ively obtained Full Scale Wechsler Adult Intelligence Scale scores . Ability correlated with cerebral volume , but the relationship depended on the realm of intelligence studied , as well as the sex and hemispheric functional lateralization of the subject . General verbal ability was positively correlated with cerebral volume and each hemisphere 's volume in women and in right-h and ed men accounting for 36 % of the variation in verbal intelligence . There was no evidence of such a relationship in non-right-h and ed men , indicating that at least for verbal intelligence , functional asymmetry may be a relevant factor in structure-function relationships in men , but not in women . In women , general visuospatial ability was also positively correlated with cerebral volume , but less strongly , accounting for approximately 10 % of the variance . In men , there was a non-significant trend of a negative correlation between visuospatial ability and cerebral volume , suggesting that the neural substrate of visuospatial ability may differ between the sexes . Analyses of additional research subjects used as test cases provided support for our regression models . In men , visuospatial ability and cerebral volume were strongly linked via the factor of chronological age , suggesting that the well-documented decline in visuospatial intelligence with age is related , at least in right-h and ed men , to the decrease in cerebral volume with age . We found that cerebral volume decreased only minimally with age in women . This leaves unknown the neural substrate underlying the visuospatial decline with age in women . Body height was found to account for 1 - 4 % of the variation in cerebral volume within each sex , leaving the basis of the well-documented sex difference in cerebral volume unaccounted for . With finer testing instruments of specific cognitive abilities and measures of their associated brain regions , it is likely that stronger structure-function relationships will be observed . Our results point to the need for responsibility in the consideration of the possible use of brain images as intelligence tests Article abstract —We examined the pattern of neuroanatomic abnormalities in adults with Down 's syndrome ( DS ) and the cognitive correlates of these abnormalities . Specifically , we compared this pattern with what would be predicted by the hypotheses attributing DS pathology to either premature aging or Alzheimer 's disease . We measured a number of brain regions on MRIs of 25 subjects : 13 persons with the DS phenotype and 12 age- and sex-matched healthy volunteers . Study participants had no history of cardiovascular disease , diabetes , thyroid dysfunction , or seizure disorder . After statistical adjustment for differences in body size , we found that , in comparison with controls , DS subjects had substantially smaller cerebral and cerebellar hemispheres , ventral pons , mammillary bodies , and hip-pocampal formations . In the cerebellar vermis of DS subjects , we observed smaller lobules VI to VIII without appreciable differences in other regions . In addition , we noted trends for shrinkage of the dorsolateral prefrontal cortex , anterior cingulate gyrus , inferior temporal and parietal cortices , parietal white matter , and pericalcarine cortex in DS subjects compared with normal controls . The parahippocampal gyrus was larger in DS subjects . We found no significant group differences in the volumes of the prefiontal white matter , the orbitofiontal cortex , the pre- and post central gyri , or the basal ganglia . We conclude that the pattern of selective cerebral damage in DS does not clearly fit the predictions of the premature aging or Alzheimer 's disease hypotheses . To examine the relationship between brain abnormalities and cognitive deficits observed in DS , we correlated the size of brain regions that were significantly reduced in DS with performance on tests of intelligence and language . The correlational analysis suggested age-related decline in the DS subjects in general intelligence and basic linguistic skills . General intelligence and mastery of linguistic concepts correlated negatively with the volume of the parahippocampal gyrus . There was no relationship between total brain size and the cognitive variables Although observational findings linking breast milk to higher scores on cognitive tests may be confounded by factors associated with mothers ' choice to breastfeed , it has been suggested that one or more constituents of breast milk facilitate cognitive development , particularly in preterms . Because cognitive scores are related to head size , we hypothesized that breast milk mediates cognitive effects by affecting brain growth . We used detailed data from a r and omized feeding trial to calculate percentage of expressed maternal breast milk ( % EBM ) in the infant diet of 50 adolescents . MRI scans were obtained ( mean age = 15 y 9 mo ) , allowing volumes of total brain ( TBV ) and white and gray matter ( WMV , GMV ) to be calculated . In the total group , % EBM correlated significantly with verbal intelligence quotient ( VIQ ) ; in boys , with all IQ scores , TBV and WMV . VIQ was , in turn , correlated with WMV and , in boys only , additionally with TBV . No significant relationships were seen in girls or with gray matter . These data support the hypothesis that breast milk promotes brain development , particularly white matter growth . The selective effect in males accords with animal and human evidence regarding gender effects of early diet . Our data have important neurobiological and public health implication s and identify areas for future mechanistic study The objective was to examine whether cerebral volumes are reduced , and in what regions , in adolescents with anorexia nervosa and to study changes after nutritional recovery . Twelve anorexia nervosa ( DSM-IV ) patients aged 11 - 17 consecutively admitted to an Eating Disorders Unit were assessed by means of  psychopathological scales  , neuropsychological battery and voxel-based morphometric ( VBM ) magnetic resonance imaging at admission and after 7 months ' follow-up . Nine control subjects of similar age , gender and estimated intelligence level were also studied . The two groups showed differences in gray matter ( F=22.2 ; p<0.001 ) and cerebrospinal fluid ( CSF ) ( F=21.2 ; p<0.001 ) but not in white matter volumes . In anorexic patients , gray matter volume correlated negatively with the copy time from the Rey Complex Figure Test . In the regional VBM study several temporal and parietal gray matter regions were reduced . During follow-up there was a greater global increase in gray matter ( F=10.7 ; p=0.004 ) and decrease in CSF ( F=22.1 ; p=0.001 ) in anorexic patients . The increase in gray matter correlated with a decrease in cortisol ( Spearman correlation=-0.73 ; p=0.017 ) . At follow-up there were no differences in global gray matter ( F=2.1 ; p=0.165 ) , white matter ( F=0.02 , p=0.965 ) or CSF ( F=1.8 ; p=0.113 ) volumes between both groups . There were still some smaller areas , in the right temporal and both supplementary motor area , showing differences between them in the regional VBM study . In conclusion , in adolescent anorexic patients  gray matter is more affected than white matter and mainly involves the posterior regions of the brain . Overall gray matter alterations are reversible after nutritional recovery 
    Output:
    
We show that the strength of the positive association of brain volume and IQ has been overestimated in the literature , but remains robust even when accounting for different types of dissemination bias , although reported effects have been declining over time .
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 an isomorphic proxy of human intelligence differences