Biomedical subjects

F Aboitiz

Publications and source records attributed to F Aboitiz.

At least 19 recordsLinked to original sources

PubMed1995

Working memory networks and the origin of language areas in the human brain.

Temporoparietal-prefrontal working memory networks are proposed as fundamental in the evolutionary origin of the language regions. Having a primordial capacity to name objects or situations, primitive hominids may have strongly benefited from the possibility to recall past events from memory, in order to refer to them through vocal communication. Working memory cortical networks are related to these types of tasks, and are arranged quite similarly to the language networks in the brain. It is possible that the language areas and their connections arose as a local specialization of these large-scale cortical networks, that developed as neural strategies to recall past events to be shared in community. The origin of syntax may have taken place after these networks were sufficiently stabilized, and (at least originally) may have been related to aspects of vocal motor control, involving the progressive differentiation of the anterior language areas and their connections.

Biological Evolution↗

PubMed1994

The evolution of brain size and organization in vertebrates. A program for research.

In vertebrates, brain size variability relates to two main parameters: body size and ecological factors (in particular diet and foraging strategy). It has been considered by many authors that evolutionary brain growth is a unitary phenomenon whose main effect is to increase processing capacity. Alternatively, in this paper it is considered that brain growth is significantly associated with higher processing capacity only when it occurs associated with ecological circumstances (selection of behavioral or perceptual skills). This process is referred to as "active" growth. When the brain scales on body size, there is little change in processing capacity, and this will be referred to as "passive" growth. I propose that these two modes of phylogenetic brain growth relate to different developmental/evolutionary processes and are distinguishable at the level of adult and developing structure. Shortly, growth due to selection of behavioral capacities is associated with more differentiated brains in terms of number of areas, connectional rearrangements and cell types. Growth due to scaling of body mass produces little brain rearrangements, and many of those that occur relate to the maintenance of functions in a larger brain. In addition, active selection of brain size is triggered by plastic, ontogenic rearrangements of connectivity in the organisms, while passive growth produces the minor rearrangements that take place. Finally, I propose a research program oriented to test this model by separating the effects of body size and ecological variables in brain organization across species.

Adaptation, Physiological↗

PubMed1993

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Animals↗

PubMed1993

Further comments on the evolutionary origin of the mammalian brain.

This paper is an extension of a previous report on the origin of the mammalian neocortex. Two main aspects are elaborated. The first is the evolution of visual projections from the midbrain to the telencephalon, featuring the encephalization of visual functions. Associated to this, the progressive fusion of the two main visual systems (thalamofugal and tectofugal) in the mammalian telencephalon (striate and extrastriate cortex, respectively) is viewed in the context of increasing cortico-cortical connectivity in the evolution of the mammalian brain. In addition, the issue of a presumed homology between mammalian extrastriate cortex and reptilian anterior dorsal ventricular ridge (ADVR) is reviewed in some detail, and it is concluded that extrastriate cortex is a derived character of mammals while ADVR is a derived character of reptiles and birds. It is not likely that ADVR is ancestral to extrastriate cortex. The second aspect under analysis is the origin of the inverted (inside-out) lamination pattern of mammalian neocortex that differs from the outside-in pattern of reptilian cortex. Furthermore, mammals have developed a transient embryonic cell layer (the subplate zone) that serves as a waiting compartment for thalamic and cortico-cortical axons while their prospective target cells end their migration process to reach their final positions. It is postulated that both, inverted lamination and the subplate zone arose in evolution as successive and complementary strategies to maximize synaptic contacts between thalamic afferents and the new cortical cell types (belonging to prospective granular and supragranular layers) that were being originated at that moment.

Animals↗

PubMed1992

Fiber composition of the human corpus callosum.

The densities of fibers of different sizes were calculated in ten regions of the corpus callosum of twenty human brains (ten females, ten males). Light microscopic examination revealed a consistent pattern of regional differentiation of fiber types in the corpus callosum. Thin fibers are most dense in the anterior corpus callosum (genu), and decrease in density posteriorly towards the posterior midbody, where they reach a minimum. Towards the posterior corpus callosum (splenium), the density of thin fibers increases again, but in the posterior pole of the callosum the density decreases locally. Large-diameter fibers show a pattern complementary to that of thin fibers, having a peak of density in the posterior midbody and a local increase of density in the posterior pole of the corpus callosum. Across subjects, the overall density of callosal fibers had no significant correlation with callosal area and an increased callosal area indicated an increased total number of fibers crossing through. Considering different fiber sizes, this was only true for small diameter fibers, whose large majority is believed to interconnect association cortex. No sex differences in fiber composition of the corpus callosum were found.

Adult↗

PubMed1992

Individual differences in brain asymmetries and fiber composition in the human corpus callosum.

There have been several recent reports concerning individual differences in the gross morphometry of the human corpus callosum. However, no studies exist on individual differences in the fiber composition of the corpus callosum. Here we report for the first time the relation of fiber composition in specific callosal segments (as seen in light microscopy) to anatomical asymmetries in language-gifted cortex, as a function of sex. We found a significant negative correlation between Sylvian fissure asymmetries and the total numbers of fibers in the isthmus of males, and in the anterior splenium of females. In addition, a population of relatively large fibers (between 1 micron and 3 microns in diameter) in the isthmus showed a strong negative correlation with perisylvian asymmetries only in males. These findings suggest a sex-dependent, pathway-specific decrease in interhemispheric connectivity with increasing lateralization.

Adult↗

PubMed1992

The origin of the mammalian brain as a case of evolutionary irreversibility.

The origin of the mammalian neocortex is usually considered as an improvement in the design of the brain. I suggest that the mammalian neocortex arose as a consequence of contingent adaptations in which there was no specific selection for more elaborate cognitive abilities. This perspective differs from the current view of brain evolution as a progressive phenomenon towards increased intelligence.

Animals↗

PubMed1992

Mechanisms of adaptive evolution. Darwinism and Lamarckism restated.

This article discusses the conceptual basis of the different mechanisms of adaptive evolution. It is argued that only two such mechanisms may conceivably exist, Lamarckism and Darwinism. Darwinism is the fundamental process generating the diversity of species. Some aspects of the gene-centered approach to Darwinism are questioned, since they do not account for the generation of biological diversity. Diversity in biological design must be explained in relation to the diversity of interactions of organisms (or other higher-level units) with their environment. This aspect is usually overlooked in gene-centered views of evolution. A variant of the gene-selectionist approach has been proposed to account for the spread of cultural traits in human societies. Alternatively, I argue that social evolution is rather driven by what I call pseudo-Lamarckian inheritance. Finally, I argue that Lamarckian and pseudo-Lamarckian inheritance are just special cases of faithful replication which are found in the development of some higher-order units, such as multicellular organisms and human societies.

Adaptation, Physiological↗

PubMed1992

Morphometry of the Sylvian fissure and the corpus callosum, with emphasis on sex differences.

The relationship between anatomical asymmetries in the perisylvian region and the sizes of different regions of the corpus callosum was investigated post-mortem in 40 brains of right-handed hospital admissions (20 males, 20 females) with no cortical involvement. There were no sex differences either in anatomical asymmetries or in regional size of the callosum. There was a negative correlation between the absolute value of Sylvian fissure (planum temporale) asymmetries and the size of the isthmus in males but not in females. Further, there was a significant negative correlation between the size of the Sylvian fissure (or planum temporale) and the size of the callosal mid-body in males but not in females. There was no correlation between the asymmetry of the planum temporale magnitude of left-right and total size of the planum (left+right). These findings constrain theories about the ontogenesis of hemispheric specialization through changes in callosal connectivity and about sex differences in interhemispheric organization.

Adult↗

PubMed1992

The evolutionary origin of the mammalian cerebral cortex.

The origin of the mammalian neocortex in usually considered as an improvement in the structure of the brain. Alternatively, I suggest that the mammalian neocortex arose as a consequence of contingent adaptations in which there was no specific selection for more elaborate cognitive abilities. In primitive mammals, the adaptation to nocturnal life produced a reduction of the optic tectum (superior colliculus). In addition, the development of the olfactory system triggered the development of the cerebral cortex. It is proposed that, since both the optic tectum and the cerebral cortex are laminar structures, the growing cortex replaced the tectum in many integratory functions. When mammals reinvaded diurnal niches, the optic tectum did not redevelop, and the cerebral cortex remained the main integratory and perceptual system. This is a case of irreversible reduction of an organ. In reptiles and especially in birds, although there was also an increase in brain size (associated with higher cognitive capacities), the optic tectum grew in size and complexity and the forebrain grew largely as a nonlaminar structure (except the Wulst in birds). Therefore, the origin of the cerebral cortex resulted from the combination of adaptations to nocturnality and the development of olfactory-driven behavior, and its origin is not directly related to higher cognitive capacities.

Animals↗

PubMed1992

Brain connections: interhemispheric fiber systems and anatomical brain asymmetries in humans.

The present review summarizes some results of a research program oriented to determine the anatomical substrates of interhemispheric communication in humans, as seen in postmortem material. One main finding is a sensible pattern of histological differentiation along the corpus callosum, indicating specific properties of interhemispheric conduction for axonal fibers involved in different brain functions. Callosal regions that connect primary and secondary sensory and motor areas are characterized by a large proportion of fast-conducting, large-diameter fibers, while regions connecting the so-called association areas and prefrontal areas bear a high density of slow-conducting, lightly myelinated and thin fibers. These findings are interpreted in a functional context, suggesting that the fast-conducting fibers connecting sensory and motor areas contribute to fuse the two hemirepresentations in each hemisphere. It has also been determined that an increased callosal area indicates an increased number of callosal fibers, a finding that validates previous morphometric studies done in several laboratories. No sex differences in callosal size, shape, or in callosal fiber composition were found. Finally, an inverse relation was found between the anatomical asymmetries in the size of the Sylvian fissure and the size and number of fibers in specific segments of the corpus callosum. There were sex differences in terms of the particular callosal regions showing a significant correlation with asymmetries, and in terms of the fiber types that were correlated with asymmetries.

Animals↗

PubMed1991

Lineage selection and the capacity to evolve.

The capacity of genetic recombination is an unusual adaptive trait since it is based on the capacity to produce evolutionary change rather than on the capacity to produce better performing individuals. The evolution of this character has been considered to be a case of group or species selection. Alternatively, I introduce a new concept, lineage selection, to account for the evolution of this trait.

Animals↗

PubMed1990

Behavior, body types and the irreversibility of evolution.

A functional approach to evolutionary morphology is emphasized in this paper. This perspective differs from the current 'structuralist' trend, which emphasizes the constraining role of developmental paths. In addition, the present approach agrees with the adaptationist paradigm. It is further argued that three types of phenomena are better understood in this light: i. The existence of evolutionary trends, ii. The maintenance of certain structural features within a given taxon, and iii. The irreversibility of evolution.

Animals↗

PubMed1989

Behavior, archetypes and the irreversibility of evolution.

There is a tendency in modern evolutionary theory to treat organisms as organized by genetic and developmental interactions, in such a way that these play a major role determining the direction of morphological evolution. Alternatively, in this paper behavior is considered as the most fundamental cohesive factor in the morphological evolution of animals. Some phenomena, such as the existence of evolutionary trends, the maintenance of architectural types in certain taxa, and the irreversibility of evolution are discussed in this light.

Adaptation, Physiological↗

PubMed1989

[Cerebral laterality and interhemispheric connections: neurobiologic aspects].

This review summarizes evidence favouring two kinds of anatomical correlates of cerebral lateralization. The first, cortical asymmetries, is widely accepted today. It is now known that there are significant asymmetries in brain regions corresponding to the so-called "language areas". These asymmetries are present at the level of gross anatomy (i.e., length of the Sylvian fissure), and at a more detailed cytoarchitectonic level. Furthermore, it is known that, in different subjects, the extent of the asymmetries correlates well with the degree of functional lateralization. The second anatomical variable is commisural connectivity. The corpus callosum has been postulated as pivotal in the workings of a lateralized brain. There have been controversial reports suggesting a correlation between callosal structure and parameters related to brain lateralization, such as sex and handedness. Together with analysing these results, this review considers some aspects of the fine structure and development of the corpus callosum. These considerations lead to the proposal of specific hypotheses about the relation between brain lateralization and commisural connectivity.

Brain↗

PubMed1988

Homology: a comparative or a historical concept?

The meaning of the word 'homology' has changed. From being a comparative concept in pre-Darwinian times, it became a historical concept, strictly signifying a common evolutionary origin for either anatomical structures or genes. This historical understanding of homology is not useful in classification; therefore I propose a return to its pre-Darwinain meaning.

Animal Population Groups↗

PubMed1988

Epigenesis and the evolution of the human brain.

This article proposes an hypothesis for the evolution of the human brain. It is based on the concepts of (i) regulation of nerve cell proliferation, and (ii) selective stabilisation of synapses during development. The former process is supposed to be rigidly regulated by the genome, while the latter (selective stabilisation) is proposed as developing in a more plastic manner. It is suggested here that genetic alterations of the regulation of neuroblast proliferation led to epigenetic rearrangements in selective synapse stabilisation, thus producing significant changes in cerebral connectivity. This view is in agreement with the punctuationalist theory of human evolution, and differs from other approaches to human nature, such as structuralist grammar and sociobiology.

Biological Evolution↗

PubMed1986

Histological asymmetry in the primary visual cortex of the rat: implications for mechanisms of cerebral asymmetry.

The present study was designed to specify the contributions of various histological parameters to hemispheric asymmetry of architectonic areas. It was found that the primary visual cortex of the rat is asymmetrical in volume, and that the asymmetry reflects side differences in the number of neurons. The implications of this finding for the understanding of mechanisms involved in the production of brain asymmetries are discussed.

Animals↗