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M A Hofman

Publications and source records attributed to M A Hofman.

At least 73 records · Page 4Linked to original sources
PubMed1989

The sexually dimorphic nucleus of the preoptic area in the human brain: a comparative morphometric study.

The sexually dimorphic nucleus of the preoptic area (SDN-POA) in the human hypothalamus is an ovoid, densely packed collection of large cells. The size, shape and cellular morphology of the SDN-POA was examined in relation to sex and age in adult human subjects. In this region the following parameters were measured: length of the rostrocaudal axis, maximum cross-sectional area, volume, numerical cell density, total number of cells, and the diameter of the cell nucleus. The SDN-POA was elongated in females and more spherical in males. The mean volume and total cell number were markedly sexually dimorphic: the volume of the SDN-POA was 2.2 times as large in males as in females and contained 2.1 times as many cells. No sex differences were observed in either cell density or mean diameter of the cell nuclei. Furthermore, multivariate regression analysis revealed that there are also sex-linked differences in the structural organisation of the human SDN-POA, finding expression in the way the morphometric parameters are interrelated. Of the parameters measured, only the volume and cell number of the SDN-POA showed a dramatic decrease with ageing. The reduction in cell number, however, was not constant throughout adulthood but was found to depend upon sex and age. In males, a major reduction in SDN-POA cell number was observed between the age of 50-60 years. In females, cell death was found to be more prominent than in males, especially among old people (t greater than 70 years), dropping to values which were only 10-15% of the cell number found in early childhood. In conclusion, the human SDN-POA has a sex-dependent pattern of ageing. Finally, the morphology of the SDN-POA was compared with that of other hypothalamic regions--the suprachiasmatic nucleus (SCN) and the paraventricular nucleus (PVN)--both in man and in rat. Species-specific differences in the dimensions of these nuclear regions are discussed in the light of their assumed functional significance.

Adolescent↗
PubMed1988

Sexual differentiation of the human hypothalamus: ontogeny of the sexually dimorphic nucleus of the preoptic area.

Sexual differentiation of the hypothalamus of the human brain is generally believed to take place around midpregnancy and thought to be related to the development of sexual orientation and gender identity. The present life span study on the human sexually dimorphic nucleus (SDN) of more than a hundred subjects revealed, however, that at the age of 2-4 years the SDN cell number reaches a peak value, and that only after this age sexual differentiation becomes manifest. Furthermore, the SDN cell number in homosexual men was not different from that of the male reference group, but significantly larger than the cell number in age-matched women.

Adolescent↗
PubMed1988

Size and shape of the cerebral cortex in mammals. II. The cortical volume.

The geometry of the brain and cerebral cortex in mammals has been studied from an evolutionary perspective and is described in mathematical terms. The volume of the cerebral cortex, in contrast to the cortical surface area, scales to brain volume in a similar way, irrespective of the degree of cortical folding. Among mammals, Cetacea form a subgroup, in that their volumetric data fit an isometric model better than an allometric model. An index of corticalization is presented which contains information about both the mass of interconnective nerve fibers and the degree of intracortical processing. It is shown, furthermore, that a semilogarithmic equation appropriately describes the relationship between mean cortical thickness and brain volume. Finally, allometric equations between brain volume and cortical parameters, which can be used for predictive purposes, are presented.

Animals↗
PubMed1988

Morphometric analysis of the suprachiasmatic and paraventricular nuclei in the human brain: sex differences and age-dependent changes.

The size, shape and cellular morphology of the suprachiasmatic (SCN) and paraventricular nuclei (PVN) in the human hypothalamus were examined in relation to sex and age. In both nuclear regions the following parameters were determined: length of the rostrocaudal axis, maximum cross sectional area, volume, numerical cell density, total number of cells and the diameter of cell nuclei. No sexual difference was observed in any of these parameters, either in the SCN or in the PVN, with the exception of a sexual dimorphism in the shape of the SCN. In contrast to the absolute measurements, sexual differences were found in the internal structural organisation of these hypothalamic nuclei using multivariate regression analysis. Of the parameters measured only the volume of the SCN in females showed a continuous decrease with ageing, whereas the changes in the other variables were not consistent. Regression analysis revealed that this decrease in SCN volume is mainly caused by cell loss rather than by a reduction in cell size. Finally, a comparison of the volumetric measurements of the human SCN and PVN with those of the rat showed that the human SCN is reduced in size relative to other hypothalamic nuclei. Possible consequences of this phenomenon for the functional significance of the SCN in man are discussed.

Adolescent↗
PubMed1987

Effects of neonatal thermal lesioning of the mesocortical dopaminergic projection on the development of the rat prefrontal cortex.

The role of dopamine (DA) in the development of the prefrontal cortex (PFC) was investigated by depleting the dopaminergic innervation of the PFC. A new stereotaxic procedure made it possible to produce small lesions in 1-day-old rats confined to the A10 group of dopaminergic cell bodies in the ventral tegmentum, from which the dopaminergic projection to the PFC originates. The variety in the lesions revealed a clear topographical organization of the efferent connections of the ventral tegmental area (VTA) to the prefrontal cortex. As far as we know from the literature the data presented in this study are a first direct indication of a neurotrophic role for dopamine in the development of the prefrontal cortex. When the prefrontal cortex was depleted of the dopaminergic innervation from birth on, by lesioning the cells of origin on postnatal day 1, the cortical thickness in the medial PFC was reduced by about 6%. Although coagulative lesions in the ventral tegmentum cause also a depletion of cortical serotonin, cortical reduction seems to be rather the result of the absence of dopamine during its development. This is indicated by the absence of a significant cortical thickness reduction in the dysgranular part of the first somatosensory cortex, which receives a serotonergic but no dopaminergic innervation.

Animals↗
PubMed1986

Morphometry of size/volume variables and comparison of their bivariate relations in the nervous system under different conditions.

Comparison of the different approximation equations and procedures to estimate the volume of a brain region with an irregular shape contained in parallel sections indicates that the 'basic volume estimator' using systematic section is very efficient and sufficiently accurate. Important in estimating the volume is the correction for shrinkage and the accuracy of the section thickness determination. Methods to estimate thickness of section are outlined, and the method of differential focusing is discussed. In the Appendix, the corrections are described for overestimation of the volume by overprojection of the cross-sectional area and underestimation by underprojection when the size of cross-sectional area changes non-negligibly within sections. Statistical techniques to compare bivariate linear relations of different groups are reviewed. Emphasis is laid on Model II regression techniques that are used when the two variables considered are both subject to biological variation and measurement error. A new Model II procedure is proposed to compare the coincidence of the slopes of bivariate distributions and to test whether or not an experimental bivariate sample deviates significantly from a control sample when only the control group shows a significant bivariate linear relationship.

Animals↗
PubMed1986

Bivariate linear models in neurobiology: problems of concept and methodology.

Bivariate linear models, used to describe morphological and functional characteristics between two sets of observations, are examined both in concept and in application. This paper focuses on the underlying assumptions and statistics of the method most frequently used: ordinary linear regression, principal axis and standard major axis. It is shown how the choice of method should depend on: the purpose of the analysis and the a priori assumptions regarding the residual variance. It appears that none of the methods has a universal application. Differences among the models discussed are illustrated by a bivariate morphometric analysis of cerebrocortical regions in primates.

Animals↗
PubMed1985

Neuronal correlates of corticalization in mammals: a theory.

The cerebral cortex of mammals has been found to be uniformly organized, and to be composed of elementary processing units or modules having an essentially constant number of neurons. In the present paper the hypothesis is put forward that the relative proportion of local circuit neurons (LCNs) within a module reflects the evolutionary level of corticalization of a mammal. The modules, in turn, are interconnected so as to form basic neuronal networks or columns with a species-specific width varying from 90 to 310 microns. A mathematical formalism is presented from which the hypothetical ratio between LCNs and projection neurons, as well as the size of the cortical column and the number of modular units that it contains, can be calculated.

Animals↗
PubMed1985

Size and shape of the cerebral cortex in mammals. I. The cortical surface.

The evolution of the brain in mammals has been accompanied by a progressive enlargement of the cerebral cortex. Allometric analysis of the volume, surface and convolutedness of this cortex shows that among mammals two major groups can be distinguished: (1) species with lissencephalic brains, where surface-volume relationships are determined by linear geometric laws, and (2) species with gyrencephalic brains, where strict geometric similarity no longer applies. Different mathematical models are required to describe the brain morphology in these groups. It has been shown, moreover, that among species with convoluted brains, marine mammals (Cetacea) form a subgroup in that the cerebrocortical surface in these animals is more folded than in terrestrial mammals of similar brain size. Thus it appears that the use of a single allometric relation in studying the effect of size increase on the geometry of the brain - irrespective of convolutedness or ecological strategy - as has been done in previous studies, is unjustified and obscures the differences in the structural organization of mammalian brains. Finally, a dimensionless index of cortical folding is proposed, which indicates that the degree of cortical folding depends not only on the volume of the brain or cortex but on cortical thickness as well.

Animals↗
PubMed1984

A biometric analysis of brain size in micrencephalics.

Brain weight and head circumference in micrencephalic patients were analysed as a function of age, height and sex in relation to normal human standards. A quantitative definition of micrencephaly is proposed, which is based on these analyses. Evidence is presented, furthermore, that micrencephalics have a significantly lower brain weight in adolescence than in early childhood, and that this cerebral dystrophy continues throughout adulthood, leading to death in more than 85% of the males and 78% of the females before they reach the age of 30 years. Since this decline in brain weight after approximately 3-5 years of age is not accompanied by a similar reduction in head circumference, the brains of elderly micrencephalic patients no longer occupy the entire cranial cavity. It is evident, therefore, that head circumference in the case of micrencephaly is an unsuitable parameter for estimating brain size.

Age Factors↗
PubMed1984

Energy metabolism and relative brain size in human neonates from single and multiple gestations. An allometric study.

From an allometric analysis of single and multiple human pregnancies the metabolic rate and the degree of encephalization of neonates could be calculated. As a result of the reduction in somatic growth in multiple gestations the oxygen consumption per neonate was found to be an inverse non-linear function of litter size. Furthermore, differential growth rates between brain weight, body weight, and body length, respectively, in the late prenatal period revealed that twins at birth are in general less encephalized than are newborns from single births.

Birth Weight↗
PubMed1983

Evolution of brain size in neonatal and adult placental mammals: a theoretical approach.

An index of encephalization has been proposed for neonatal placental mammals, indicating the progress of relative brain size of a species at birth. It appears that the neonatal index is directly proportional to neonatal brain weight and an inverse linear function of the metabolic rate of the newborn. An identical relationship has recently been found for adult mammals. A further inquiry has been made into the allometry of gestation time, litter size, neonatal brain weight and maternal metabolic rate. A hypothetical model in which these variables were incorporated reveals that the maternal energy supply to the fetal mass is the principal determining factor in setting limits to the length of gestation.

Animals↗
PubMed1983

Energy metabolism, brain size and longevity in mammals.

The mathematical relations between basal energy metabolism, brain size, and life span in mammals have been investigated. The evolutionary level of brain development, or encephalization (c), is a function both of brain weight (E) and of body weight (P) according to (formula; see text) Brain weight was found to be a linear function of the product of encephalization and basal metabolic rate. The oxygen consumption of the brain (Mbrain) is proportional to both encephalization and body weight according to (formula; see text) The ratio of metabolic rate in the cerebral cortex to that in the brain as a whole depends solely upon the degree of encephalization and is independent of the size of the animal. The maximum potential life span of a mammal was found to be proportional to the product of its degree of encephalization and the reciprocal of its metabolic rate per unit weight. Life span may be regarded as the algebraic sum of two components: (1) a deduced somatic component (Lb) inversely related to the basal metabolic rate per unit weight, and (2) an encephalization component (Le) related directly to the evolutionary increase of relative brain size.

Animals↗
PubMed1983

Encephalization in hominids: evidence for the model of punctuationalism.

A progressive enlargement of the hominid brain started 3-2 million years ago, probably from a gracile australopithecine form. Since then, three major transitions in degree of encephalization have taken place, leading to modern Homo sapiens. In the present study it is shown that these transitions must have occurred in rapid bursts, interspersed with long periods of little or no evolutionary change (stasis). This stepwise mode of encephalization is in accordance with the model of punctuated evolutionary change. A further inquiry has been made into the size of the cerebral cortex of hominids and into the number of cortical neurons based on estimates which were derived from allometric equations in extant mammals.

Anthropometry↗
PubMed1982

Encephalization in mammals in relation to the size of the cerebral cortex.

A new index of encephalization has been proposed based on a reanalysis of the brain-body weight relationship in mammals. The new index, c, is related to the volume of the whole brain as well as to the surface and volume of the cerebral cortex. From an evolutionary point of view the index-cortex relationship is particularly interesting, since the structure of the brain which contributes most to its evolutionary progression is the cerebral cortex. A theory of corticalization has been developed in which the surface of the cerebral cortex is analyzed into two components, Sb, determined by the size of the animal, and Se, associated with an increase in the information-processing capacity. An analogue division has been performed for the cortical volume. Furthermore, an inquiry has been made into the brain structure which can serve as an estimator of body weight. The medulla oblongata appears to be such a structure.

Animals↗