PubMed Health⌕ Search

Biomedical subjects

S F Witelson

Publications and source records attributed to S F Witelson.

At least 19 recordsLinked to original sources
PubMed2005

Intelligence and brain size in 100 postmortem brains: sex, lateralization and age factors.

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 samples 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 prospectively 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-handed men accounting for 36% of the variation in verbal intelligence. There was no evidence of such a relationship in non-right-handed 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-handed 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.

Aged↗
PubMed1995

Women have greater density of neurons in posterior temporal cortex.

Cytoarchitectonic area TA1 (von Economo) in the cortex of the planum temporale within the Sylvian fissure, which is auditory association cortex and documented to be part of the neural substrate of language functions, was studied quantitatively in the brain specimens of five women and four men (mean age of 50 year). All cases were documented to be medically and cognitively normal, and consistently right-handed. We investigated the possibility that the difference in brain size between men and women is reflected in differences in the numerical density of neurons in area TA1, an area associated with morphologic and psychological sex differences. Neuron counts were made directly through cell differentiation under the microscope from Nissl-stained sections. Cortical depth, the number of neurons through the depth of cortex under 1 mm2 of cortical surface (Nc), and the number of neurons per unit volume (Nv) were obtained for the total cortex and for each of the six layers in each hemisphere. For total cortex in both hemispheres, depth and Nc were similar, but Nv was greater by 11% in women, with no overlap of scores between the sexes. The sex difference in Nv was attributable to layers II and IV; in contrast, Nv did not differ between the sexes in layers III, V, and VI. This is the first report of such a sex difference in human cortex. The results suggest that the cortical functional unit has a different ratio of input and output components in men and women which could have implications for the sex differences in cognition and behavior. Due to the small sample size and the homogeneity of the cases studied, generalizability of the results requires replication by other studies. In addition, cytoarchitectonic mapping indicated that area TA1 also occurs in the vertical posterior wall of the Sylvian fissure, providing evidence that anatomical definition of the planum temporale should include the posterior vertical wall of the superior temporal gyrus.

Adult↗
PubMed1994

Functional cerebral asymmetry and sexual orientation in men and women.

Functional cerebral asymmetry was assessed in 32 gay men and 32 heterosexual men and in 30 lesbians and 30 heterosexual women with a linguistic dichotic listening test. All groups showed the typical greater right-ear accuracy and, by inference, left-hemisphere representation for language functions. As shown repeatedly in previous studies (e.g., M. P. Bryden, 1982), among heterosexuals, consistent-right-handers showed greater perceptual asymmetry than did non consistent-right-handers. In contrast, gay men and lesbians did not show an association between hand preference and magnitude of perceptual asymmetry. The results indicate different patterns of functional cerebral asymmetry in gay men and lesbians compared with heterosexual people and specifically, less association between motoric and linguistic components of cerebral asymmetry. This suggestion of atypical patterns of functional asymmetries is consistent with previous results of an increased prevalence of left-hand preference among gay men and lesbians compared with the heterosexual population (C. M. McCormick, S. F. Witelson, & E. Kingstone, 1990; C. M. McCormick & S. F. Witelson, 1991). The finding of an association between aspects of functional asymmetry, a neurological characteristics likely present from birth, and sexual orientation suggests that a neurobiological factor is involved in the origins of sexual orientation.

Adolescent↗
PubMed1992

Sylvian fissure morphology and asymmetry in men and women: bilateral differences in relation to handedness in men.

The anatomy of the sylvian fissure in the human brain was studied to develop reliable criteria for anatomical landmarks of the posterior part of the fissure for use in its definition and measurement; to quantify right-left asymmetries in segments of the sylvian fissure; to assess whether any anatomical features are associated with hand preference (selected as one index of hemispheric functional asymmetry); and whether structure-function relationships are similar in men and women. A sample of 67 brain specimens (24 men and 43 women, mean age = 53 years) was studied postmortem (with the aid of dissection) from people who had been tested before death for detailed hand preference. Sylvian fissure anatomy in the human brain is very variable and no agreement exists as to the point of its posterior termination. The posterior ascending ramus, originating at the posterior bifurcation of the fissure, was found to be the continuation of the main limb of the sylvian fissure. Three segments of the sylvian fissure were defined and measured: anterior, horizontal, and vertical. The anterior segment showed no asymmetry; the horizontal segment was twice as large on the left side as on the right; and the vertical segment twice as large on the right. The two asymmetries counterbalanced each other, and overall asymmetry in the posterior region (horizontal plus vertical) was minimal. The basic asymmetry is in the position at which the fissure turns up, resulting in the different extent and position of the surrounding right and left parietal and temporal gyri and associated cytoarchitectonic regions. The possible embryological course of the asymmetry is discussed. Handedness correlated with anatomy of the sylvian fissure in men. In contrast to general expectation, hand preference was associated with a bilateral feature of morphology, and not with less asymmetry in non-right-handers. Men having consistent-right-hand preference had longer horizontal segments in both hemispheres compared to men not having consistent-right-hand preference. The direction and magnitude of asymmetry did not differ between the two male hand-preference groups. Since hand preference is an index of other motor and perceptual functions which are asymmetrically represented in the two hemispheres in gyri surrounding the sylvian fissure, it is suggested that anatomy of the sylvian fissure is related to functional asymmetries in men. A sex difference in structure-function relationship was observed. No association was found between hand preference and sylvian fissure anatomy in women.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain↗
PubMed1991

The relationship of hand preference to anatomy of the corpus callosum in men.

Area of the midsagittal section of the corpus callosum, particularly in the region of the isthmus, was found previously to be greater in non-consistent-right-handed than consistent-right-handed men in a sample of 15 postmortem cases. Seven cases were obtained subsequent to this analysis. The new cases showed the same association previously observed between hand preference and area of the corpus callosum and its isthmus. In addition, a high negative correlation was found between isthmal area and a quantitative score of the direction and magnitude of hand preference. In the new cases, handedness was predicted better than chance using statistical functions of callosal anatomy derived from the previous group of 15 cases. These results support a relationship between variation in callosal anatomy and handedness in men and the hypothesis of a relationship between callosal morphology and functional asymmetry. The lack of such a relationship among women suggests that the developmental mechanisms leading to callosal anatomical variation in relation to lateralization are influenced by sex hormones. Methodological issues in the use of magnetic resonance imaging for the quantitative study of callosal anatomy are discussed.

Autopsy↗
PubMed1991

Left out axons make men right: a hypothesis for the origin of handedness and functional asymmetry.

The origin and underlying mechanisms of hand preference are still unresolved, despite extensive research and discussion. Numerous possibilities have been considered, including genetic and hormonal factors, brain insult and learning. We suggest here that naturally occurring loss of axons of the corpus callosum (either symmetric or asymmetric, with or without neuron death) may be one mechanism underlying the embryological development of hand preference and hemispheric anatomical and functional asymmetries in males. We note supporting evidence for this hypothesis from a report of increased prevalence of left-handedness in children born prematurely at the gestational age prior to the likely onset of axon loss. The practical implications of this hypothesis for clinical management in neonatal intensive care units are discussed. It is suggested that the course of loss of callosal axons may have a genetic component which is associated with a sex-related influence and which is modifiable by prenatal and early postnatal events.

Axons↗
PubMed1991

A cognitive profile of homosexual men compared to heterosexual men and women.

Matched groups of homosexual men, heterosexual men, and heterosexual women (n = 38 per group) were tested on three measures of spatial ability and two measures of fluency that typically reveal sex differences. For the three spatial tests and one of the fluency tests, the mean performance of homosexual men fell between those of the heterosexual men and women. The pattern of cognitive skills of homosexual men was different from that of heterosexual men: homosexual men had lower spatial ability relative to fluency. The cognitive pattern of homosexual men was not significantly different from that of heterosexual women. In addition, the results suggest that homosexual men classified on the basis of hand preference may form two subgroups that differ in cognitive pattern. These findings are compatible with the hypothesis that there is a neurobiological factor related to sexual differentiation in the etiology of homosexuality.

Adolescent↗
PubMed1991

Neural sexual mosaicism: sexual differentiation of the human temporo-parietal region for functional asymmetry.

Sex differences in human brain organization and behavior are documented by several converging lines of evidence based on patterns of functional asymmetry and cognitive abilities in normal adults and children, in patients with unilateral brain damage, and in clinical groups having atypical levels of sex hormones. Sex differences also exist in the structure of the human brain, and these are reviewed in detail herein. In addition, dichotomous differences, rather than just differences along a continuum, are noted in anatomical-functional correlations between men and women. Many of the anatomical differences cluster in the temporo-parietal regions of the brain, which subserve the asymmetric representation of some linguistic, motoric and spatial functions. The hypothesis is presented that development of the temporo-parietal region of the human brain is an anatomic network dependent on the organizing effects of sex hormones during embryonic or perinatal sexual differentiation, and that in each sex the pattern of functional asymmetries and cognitive attributes is differentially influenced by early sex hormone exposure. It is further suggested that the naturally occurring regressive events of cell death and axon elimination in early brain development contribute to the variation in the structure of the temporo-parietal region, and that this mechanism is differentially influenced by sex hormones in each sex. The specific, directional hypothesis put forward is that in early development of the male brain, lower levels of androgenic hormones or receptors lead to less regressive events in some brain regions, such as the temporo-parietal region, resulting in a larger isthmus of the corpus callosum, less cerebral functional asymmetry, and some cognitive correlates. Some supporting evidence for this hypothesis from neuropsychological studies of clinical groups and homosexual individuals is presented. The neuroanatomical correlate of functional asymmetry in posterior brain regions in women is not evident. The neural regressive events which occur in each sex may be related differently to lateralization. The concept of sexual mosaicism in the human brain is discussed.

Female↗
PubMed1991

Premortem and postmortem measurement to study structure with function: a human brain collection.

Basic issues concerning structure-function relationships in the normal human brain remain unresolved. For example, it is not known what structural basis may underlie the functional specialization of the two cerebral hemispheres or the variation in cognitive ability among people. The study of the general principles of gross and microscopic brain structure in relation to behavior requires direct postmortem study of samples of brain specimens from cognitively normal people for whom quantitative measures on neuropsychological scales are available. No such work has been reported. Although conceptually simple, such research is administratively complex. We present here an approach to the study of structure-function relationships involving postmortem measurements of the human brain. Our subjects were cancer patients who were ambulatory but had a poor prognosis. They agreed to participate in research involving both premortem neuropsychological testing on prospectively selected measures, and, in the event of death, an autopsy and subsequent neuroanatomical study. We describe the essential features of our method including the neuropsychological testing and processing of brain specimens, document the method's feasibility by reporting the number of subjects recruited and autopsies obtained, and discuss the possible usefulness of such research as a prototype for other studies and the various issues such research raises. The present collection of brain specimens and associated medical and neuropsychological documentation is a unique resource and, accordingly, tissue and associated documentation will be made available as a resource to neuroscientists for use in other basic research or as control cases in studies of neuropsychiatric disease.

Adult↗
PubMed1990

Left-handedness in homosexual men and women: neuroendocrine implications.

Although numerous researchers have hypothesized a biological factor in the etiology of homosexuality, there is a lack of empirical evidence. Previous investigations did not focus on behavioral functions of the brain. Using neuropsychological testing, we found an increased incidence of left-hand preference (defined as non-consistent right-hand preference) in a group of 32 homosexual women. A trend in the same direction was found in a group of 38 homosexual men. These results suggest that homosexual orientation has a neurobiological component possibly related to hemispheric functional asymmetry. The results are consistent with previous reports that (1) prenatal neuroendocrine events are a factor in the development of human sexual orientation and functional brain asymmetries, and (2) the mechanisms associated with homosexual orientation and related neuropsychological characteristics are different between the sexes, i.e. elevated levels of prenatal sex hormones in women and decreased levels in men.

Adult↗
PubMed1989

Hand and sex differences in the isthmus and genu of the human corpus callosum. A postmortem morphological study.

The midsagittal area of the corpus callosum was measured in its entirety and in seven subdivisions in a sample of 50 brains consecutively obtained from autopsies of individuals who had neuropsychological testing before death. A 12-item test of hand preference was used as an index of the pattern of interhemispheric functional asymmetry. Callosal size was analysed for two factors: hand preference, classified as consistent-right-hand preference (CRH) versus non consistent-right-hand preference, and sex. The group of nCRH (n = 18) was found to have a larger overall callosal area, with the greatest difference occurring in the posterior body segments, especially the isthmus. The isthmus probably includes interhemispheric fibres from posterior parietal and superior temporal cortex which involves cortical regions related to functional asymmetry. The results of variation in callosal morphology are discussed as part of a possible substrate of functional asymmetry and due to variation in axonal elimination in early brain development. Sex differences were found in several aspects of callosal anatomy. (1) The difference between hand groups in the posterior body occurred in interaction with sex:handedness was a factor in callosal size in males (n = 15), but not in females (n = 35). This result is consistent with the general hypothesis of females having less clear lateralization than males. (2) Females did not have a larger overall callosum or a larger splenium, either in absolute size or size proportional to brain weight. The latter measure was considered since callosal area correlated with cerebrum weight (r = 0.48). In contrast, female of both hand groups were found to have a larger proportional isthmus compared to CRH males. (3) Of all callosal regions, only the genu and a part of the anterior body were found to be larger in absolute size in males than females. (4) Callosal size decreased with chronological age in males, but not in females.

Adult↗
PubMed1987

Neurobiological aspects of language in children.

This article discusses the relevance of the study of the neurobiology of cognitive development, both for an understanding of the neural bases of cognition and of the nature of cognition itself. A key issue is the age at which hemisphere specialization first appears and whether it changes over time. The neuropsychological literature concerning language in both normal and brain-damaged children is reviewed. The usefulness of studying cognition in other clinical disorders and variation in normal cognition is indicated. The various methods used in the research are described and the methodological and interpretational difficulties arising from the diversity of groups studied and the methods used are discussed. The model is advanced that hemisphere specialization exists from birth onward and does not undergo further change in either its nature or degree. The apparent increase in the extent of hemisphere specialization during childhood is interpreted as an epiphenomenon of the increasing cognitive and behavioral repertoire of the child. Neural plasticity, assumed to underlie recovery of function, is seen as being coexistent with, but independent of, hemisphere specialization.

Brain↗
PubMed1985

The brain connection: the corpus callosum is larger in left-handers.

The size of the midsagittal area of the human corpus callosum obtained from postmortem measurement varied with tested hand preference. The corpus callosum, the main fiber tract connecting the two cerebral hemispheres, was larger by about 0.75 square centimeter, or 11 percent, in left-handed and ambidextrous people than in those with consistent right-hand preference. The difference was present in both the anterior and posterior halves, but not in the region of the splenium itself. This callosal morphology, which varied with hand preference, may also be related to individual differences in the pattern of hemispheric functional specialization. The greater bihemispheric representation of cognitive functions in left- and mixed-handers may be associated with greater anatomical connection between the hemispheres. The naturally occurring regressive events in neurogenesis, such as neuronal cell death and axonal elimination, may be factors in the individual differences in brain morphology and in functional lateralization. Specifically, right-handers may be those with more extensive early elimination of neural components.

Adult↗