Prenatal growth of the human cerebral cortex: brainprint analysis.

To construct a series of flat maps (brainprints) that document the prenatal growth of human cerebral cortex and help identify sulcal landmarks for division of cortical regions of interest (ROIs) on mapped surfaces, the authors photographed and traced histologic whole-brain slices of 25 normal human fetal brains aged 18-42 weeks gestation. Brainprints of both cerebral hemispheres from each fetus were constructed with semiautomatic brain-mapping software, and each map was divided into five ROIs based on sulcal landmarks: frontal, parietal, insular, occipital, and temporal cortices. Surface areas of cerebral hemispheres and the five ROIs were estimated. Corrected for histologic shrinkage, brainprint estimates of human fetal cortical surface area were approximately twice those of previous estimates. Cortical lobe proportions at 18 weeks appeared to be unchanged to term. Surface area estimates correlated with fetal age, brain weight, and brain volume. This collection of cortical maps may guide future quantitative analyses of cerebral hemispheric growth in premature and term infants who undergo magnetic resonance imaging, which may, in turn, help predict neurobehavioral outcomes of early cortical damage.

Brainprints: Computer-Generated Two-Dimensional Maps of the Human Cerebral Cortex in vivo.

We describe an in vivo method for the quantitative analysis of human necrotical anatomy. The technique allows unfolded regions of functional and morphological interest to be measured planimetrically. Two-dimensional cortical maps and surface area determinations derived from magnetic resonance images of monozygotic twins are presented. In addition, reconstructions and measurements of published post-mortem human and rhesus monkey hemispheres are reported. Potential applications for the study of brain organization in relation to cognitive, motor, and perceptual performance in normal and neurological populations are considered.

Topographic distribution of callosal neurons and terminals in the cerebral cortex of the cat.

This investigation had four goals: First, to study the general topography of the corpus callosum (CC) of the cat. Second, to study the columnar organization of CC terminals and map their banding pattern in the cortex. Third, to examine the relation between CC neuron density and the presence of CC terminal columns. Fourth, to determine whether CC and anterior commissure (AC) neuron distributions are intermixed. Eight adult cats were subjected to partial commissurotomies, and then to large injections of horseradish peroxidase to one cerebral hemisphere. Processing with tetramethyl benzidine revealed retrogradely labelled cells and anterogradely labelled terminals in the cortex of the uninjected hemisphere. The distributions of these cells and terminals were examined by light microscopy and analyzed by computer microscopic methods. The genu of the CC interconnects frontal portions of the cortex, the body interconnects mostly dorsal portions of the cortex, while the splenium interconnects the temporal and occipital cortices. Reconstructions of the CC terminal columns reveal intricate banding patterns in several non-primary areas of the cortex. CC cell density is greater within than outside the terminal columns. CC and AC neurons intermix in the infragranular layers of the neocortex.

Organization of the nigrothalamocortical system in the rhesus monkey.

The nigrothalamocortical connections and their topography were analyzed by autoradiography and double or triple retrograde labeling with the fluorescent dyes Fast Blue, Diamidino Yellow, and Propidium Iodide. Injections of tritiated leucine into different parts of the substantia nigra (SN) revealed that the medial SN projects to the medial magnocellular subdivisions of the ventral anterior (VAmc) and mediodorsal (MDmc) nuclei of the thalamus while the lateral SN projects to the more lateral and more posterior part of the VAmc, and the paralaminar, parvicellular, and densocellular subdivisions of the mediodorsal nucleus (MDmf, MDpc, and MDdc). With the exception of the MDmf, terminal areas observed in the mediodorsal nucleus were in the form of scattered clusters of grains. Analysis of the thalamus in cases with fluorescent dye injections into the lateral orbital gyrus (Walker's area 11), principal sulcus (area 46), anterior bank of the arcuate gyrus (areas 8 and 45), supplementary motor area (area 6), and motor cortex (area 4) revealed topographic organization of the nigrothalamocortical projection system. The parts of the VAmc and MDmc which receive afferents from the medial part of the SN in turn project to the most anterior regions of the frontal lobe including principal sulcus and orbital cortex. The lateral posterior VAmc, MDmf, MDpc, and MDdc, all of which receive afferents from the lateral part of the SN; project to more posterior regions of the frontal lobe including, in addition to the principal sulcus, the frontal eye field and also areas of the premotor cortex. These findings indicate that the SN has preferential targets in the thalamus and cerebral cortex which are segregated from those of the globus pallidus and cerebellum. Whereas the motor cortex is the primary target of cerebellar output (Asanuma et al., '83b), and the premotor cortex is the target of pallidal output (Schell and Strick, '84), the SN output appears to be directed more anteriorally--to the prefrontal cortex.

Distribution of the neurons of origin of the great cerebral commissures in the cat.

Large injections of horseradish peroxidase throughout major portions of the right cerebral hemispheres of four cats revealed extensive distributions of the neurons of origin of the corpus callosum, the anterior commissure and the hippocampal commissures in the uninjected left hemispheres. The distributions of labelled neurons were mapped by semiautomatic computer microscope. The radial and tangential neuron distributions presented here are of a higher density and greater extent than those in previously published studies based on injections of transportable label to more circumscribed areas of the cerebral cortex of the cat. Generally, commissural neurons in the cat were distributed in a bilaminar fashion with supragranular cells more numerous than infragranular cells.

Distribution of the cells of origin of the corpus callosum and anterior commissure in the marmoset monkey.

The neurons of origin of the great cerebral commissures of the marmoset monkey were identified by horseradish peroxidase histochemistry and their distribution was studied. Six adult marmosets were used. Three were normal: the others were subjected to section of the corpus callosum (CC), sparing the anterior commissure (AC). All six were injected with horseradish peroxidase throughout one cerebral hemisphere. The three normals provide information on the origins of both the CC and AC, whereas the three callosotomized monkeys allow study of the origins of the AC alone. All CC and AC neurons in the marmoset are pyramidal cells. Except for layer I, all cortical layers possess commissural cells; their laminar organization varies according to cortical area. There exists a progression in predominance from supra- to infragranular commissural neurons proceeding from temporal through occipital to parietal and finally to frontal cortex. Major acallosal zones are found in the primary visual cortex and the fore- and hindlimb representations of the somatosensory cortex. Correlations between commissural neuron distribution and cytoarchitectonic areas are not always obvious. Commissural neurons were not organized in columnar fashion.

Basal telencephalic origins of the anterior commissure of the rat.

The cells of origin of the three limbs of the rat's anterior commissure (AC) have been identified by horseradish peroxidase histochemistry. Following transection of the corpus callosum and hippocampal commissure, rats were subjected to multiple, unilateral injections of horseradish peroxidase throughout one cerebral hemisphere. The cells of origin of the rat's AC are found in the anterior olfactory nucleus, the olfactory tubercles, the anterior piriform cortex, the nucleus of the lateral olfactory tract, the lateral, basolateral, basomedial and cortical nuclei of the amygdala, the posterior perirhinal cortex, and the entorhinal cortex. Anterogradely labeled fibers were also found in the olfactory bulbs and in the plexiform layer of the anterior and posterior piriform cortices.

Neocortical and basal telencephalic origins of the anterior commissure of the cat.

The neocortical and basal telencephalic origins of the anterior commissure of the cat have not been described in earlier studies of the great cerebral commissures. In this anatomical study, all cerebral commissures, except the anterior commissure, of twelve cats were first transected. Subsequent unilateral injections of large quantities of horseradish peroxidase throughout the right hemisphere revealed the entire origins of the three branches of the anterior commissure in the left hemisphere. Since the anterior commissure was the only interhemispheric fibre system remaining, only the cells, fibres and anterogradely-labelled terminals of the anterior commissure were labelled by horseradish peroxidase in the uninjected hemisphere. Approximately three-quarters of the neurons of the anterior commissure are in the neocortex, mostly in layers V and VI. These neocortical cells occupy an extensive field stretching from gyrus proreus to the posterior ectosylvian gyrus and from the rhinal sulcus to the suprasylvian sulcus. Other fibres of the anterior commissure, however, were found to have their cell bodies in regions not considered part of the neocortex, and these included the anterior olfactory nucleus, the pyriform cortex, olfactory tubercles, nucleus of the lateral olfactory tract, part of the amygdaloid nuclei, the periamygdaloid nucleus and the lateral entorhinal area. Finally, it was found that the fibres of the anterior commissure do not have an exclusive neocortical territory from which cells of other commissural fibres are excluded. Rather, there appears to be a substantial overlap between the field of origin of fibres of the anterior commissure and those of the largest cerebral commissure, the corpus callosum. The disposition of this field may help to explain why visual information fails to transfer between the hemispheres in cats whose corpus callosum has been cut, in contrast to the success of such transfer in primates.