El papel del cuerpo calloso en el procesamiento visoespacial / The role of the corpus callosum in the visuospatial processing

El procesamiento visoespacial es una función adaptativa del organismo que permite su interacción con los elementos que se encuentran en su medio ambiente. Se considera una función superior, ya que involucra sistemas de reconocimiento y de memoria, entre otros. Hasta el momento se ha descrito la participación de diversas estructuras cerebrales en el procesamiento de información visoespacial, por ejemplo, tradicionalmente se considera una especialización funcional por parte del hemisferio derecho; sin embargo aún existen muchas controversias con respecto a la participación de diversas áreas cerebrales tanto ipsilaterales como contralaterales en estás funciones visoespaciales. En el presente trabajo se discute el papel de la comunicación interhemisferica, y específicamente del papel que juega el cuerpo calloso en el procesamiento visoespacial. Se inicia con una descripción de las vías de procesamiento visoespacial desde el ojo hasta la corteza V1 y las conexiones anatómicas funcionales que se establecen a partir de ésta. Posteriormente se resume la estructura-función del cuerpo calloso y se revisan los trabajos que han reportado relaciones entre éste y la función visoespacial. Por último, se revisan algunas de las patologías neurológicas que cursan con afectación del cuerpo calloso y que se ha reportado en la literatura que afectan a la función visoespacial...

The visuospatial processing is an adaptive function of the organism that allows it to interact with the elements that are in their environment. It is considered a high-order function as it involves recognition systems, memory, among others. So far described the participation of various brain structures in processing visuospatial information, for example, is traditionally considered a functional specialization by the right hemisphere, but there are still many controversies regarding the participation of various brain areas, both ipsilateral and contralateral in the visuospatial functions. In this paper we discuss the role of interhemispheric communication, and specifically the role of the corpus callosum in visuospatial processing. It begins with a description of visuospatial processing pathways from the eye to the cortex V1 and the anatomical-functional connections are established from this. Later summarizes the structure-function of the corpus callosum and reviews the studies that have reported relationships between this and visuospatial function. Finally we review some of the neurological disorders that present with involvement of the corpus callosum and it has been reported in the literature that affect visuospatial function...

Anatomy of corpus callosum in prenatally malnourished rats

The effect of prenatal malnutrition on the anatomy of the corpus callosum was assessed in adult rats (45-52 days old). In the prenatally malnourished animals we observed a significant reduction of the corpus callosum total area, partial areas, and perimeter, as compared with normal animals. In addition, the splenium of corpus callosum (posterior fifth) showed a significant decrease of fiber diameters in the myelinated fibers without changing density. There was also a significant decrease in diameter and a significant increase in density of unmyelinated fibers. Measurements of perimeter's fractal dimensions from sagittal sections of the brain and corpus callosum did not show significant differences between malnourished and control animals. These findings indicate that cortico-cortical connections are vulnerable to the prenatal malnutrition, and suggest this may affect interhemispheric conduction velocity, particulary in visual connections (splenium).

Long distance communication in the human brain: timing constraints for inter-hemispheric synchrony and the origin of brain lateralization

Analysis of corpus callosum fiber composition reveals that inter-hemispheric transmission time may put constraints on the development of inter-hemispheric synchronic ensembles, especially in species with large brains like humans. In order to overcome this limitation, a subset of large-diameter callosal fibers are specialized for fast inter-hemispheric transmission, particularly in large-brained species. Nevertheless, the constraints on fast inter-hemispheric communication in large-brained species can somehow contribute to the development of ipsilateral, intrahemispheric networks, which might promote the development of brain lateralization.

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

Electrophysiological evidence for an L-shaped interhemispheric connection in the cat

Transcallosal potentials evoked by electrical stimulation with rectangular pulses of 1 ms, 5 c/s and variable intensity were recorded from the cortical surface in cats anesthetized with ketamine hydrochloride. Sites of stimulation and recording were selected by means of a cartesian map of most of neocotex. In addition to the well known transcallosal projection pattern it was faund that stimulation of a restricted posterior area evokes low voltage potentials over the contralateral symmetric area while high voltage potentials are recorded from a few sites located at the ipsilateral anterior cortex and from the area symmetric as to the latter. This L-shaped transcallosal connection may be involved in complex cortical processes and is compatible with effective results of partial anterior callosotomies in patients whit multifocal epilepsy and frontal bisynchronism

An evoked potential mapping of transcallosal projections in the cat

Em dez gatos anestesiados com cetamina (Ketalar) o neocórtex foi exposto e pulsos retangulares (1 ms, 0,5Hz e intensidade variável) foram aplicados a pontos discretos de um lado enquanto se registravam os potenciais evocados no outro lado. As posiçöes de estimulaçäo e registro eram determinadas em mapa cartesiano que abrangia quase todo o neocórtex. Os potenciais foram analisados quanto aos dseus componentes, voltagem e latência. A difusäo passiva, potenciais eletrotônicos e e os efeitos do incremento da freqüência de estimulaçäo sobre os vários componentes foram analisados. Os resultados mostram a presença de grandes potenciais evocados transcalosos em algumas regiöes, com incremento de sua amplitude no sentido caudo-rostral, sendo máximos em áreas anteromediais do giro suprasilviano. Confirmando estudos anatômicos, em algumas regiöes do córtex somatomotor e visual foram registrados potenciais bastante reduzidos ou ausentes. A estimulaçäo de algumas áreas posteriores causava o aparecimento de pequenos potenciais em sua área homóloga contralateral ao mesmo tempo em que grandes potenciais eram registrados em áreas anteriores ipsi- e contralateralmente, constituindo uma conexäo em L ainda näo descrita. É possível que tal conexäo esteja implicada em alguns tipos de epilepsia e possa explicar em parte a eficácia de calosotomias parciais para seu tratamento