Richard C. Van Sluyters

Evidence for the complementary organization of callosal and thalamic connections within rat somatosensory cortex

We provide evidence that callosal projections within the primary somatosensory cortex of the rat are distributed in a detailed pattern which is complementary to the pattern of specific thalamocortical projections to this cortical region.

Unfolding and flattening the cortex of gyrencephalic brains

The present paper describes a procedure for unfolding and flattening gyrencephalic brains that makes it possible to cut single tangential sections through extensive regions of originally convoluted cortex. This procedure involves incising the arachnoid, removing the white matter, and then opening up the gyri and sulci in tissue that has been fixed in such a way as to maintain much of its natural flexibility. A technique is also described for preserving the complete gyral pattern of the intact brain on the surface of a flattened cerebral hemisphere. Finally, examples are presented in which the gyral pattern in the cat brain is related to the location of identified cortical areas in myelin-stained tangential sections from flattened material.

Widespread callosal connections in infragranular visual cortex of the rat

Following multiple injections of HRP into the posterior cortex of one hemisphere of adult rats, dense and overlapping distributions of retrogradely labeled cells and anterogradely labeled terminations are observed throughout the depth of the cortex in the region of the border between the lateral portion of area 17 and area 18 in the opposite hemisphere. In contrast to previous studies of the visual callosal pathway, we also find large numbers of labeled callosal cells extending throughout areas 17 and 18 in cortical layers Vc and VIa.

The projection from striate and extrastriate cortical areas to the superior colliculus in the rat

Following single injections of horseradish peroxidase (HRP) in the superior colliculus (SC) and [3H]proline in the striate cortex of rats, a close correspondence was observed in the topographical arrangements of extrastriate cortical fields of HRP retrograde label and of isotope anterograde label. These results support the notion that extrastriate cortex is divided into multiple physiologically and anatomically defined areas, and they suggest that these areas project separately to SC.

Axons from restricted regions of the cortex pass through restricted portions of the corpus callosum in adult and neonatal rats

It is known that development of the interhemispheric pathway is accompanied by a dramatic reduction in the number of callosal fibers. By injecting neuroanatomical tracers into the cortex of newborn and adult rats, we examined the distribution of fibers within the corpus callosum both before and after this loss takes place. We found that in both newborn and mature rats, axons from restricted regions of the cortex are grouped into relatively tight bundles within the corpus callosum and that the location of these bundles depends upon the region of cortex from which they originate. These results indicate that callosal fibers that are destined to disappear are not distributed diffusely throughout the corpus callosum of the neonate, but rather that they traverse this commissure through the sector that is appropriate for the area of the cortex from which they originate. This finding suggests that loss of axons does not play a significant role in establishing the overall topographic pattern of the fibers within the callosal commissure.

Pattern of extrastriate visual areas connecting reciprocally with striate cortex in the mouse.

Abstract Several areas reciprocally connected to striate cortex were found in the extrastriate cortex of the mouse after small single injections of horseradish peroxidase into the striate cortex. By showing that the arrangement of these labeled extrastriate areas resembles closely the physiologic and anatomic subdivision of the extrastriate cortex reported previously in several rodent species, this study supports the hypothesis that there exists a common pattern of visual cortical organization in rodents.

Analysis of monocular optokinetic nystagmus in normal and visually deprived kittens.

The asymmetry of monocular OKN was assessed in normal, monocularly deprived (non-deprived eye) and strabismic cats. No significant differences were observed between the responses of these 3 groups. In young kittens, the gain of OKN for nasalward stimulus movement was larger than that for temporalward. This asymmetry declined to a low residual level by about one year of age. Neurophysiological recordings indicated that the symmetry of OKN is not related to cortical binocularity.

Horizontal optokinetic nystagmus in the cat: Effects of long-term monocular deprivation

The effects of prolonged monocular deprivation (MD) on horizontal optokinetic nystagmus (OKN) have been examined in cats subjected to unilateral or bilateral visual cortex lesions. Presurgically , OKN elicited through the deprived eye was substantially weaker than that through the non-deprived eye. This effect was most prominent for OKN in response to temporalward stimulation, which essentially was abolished in the deprived eye. In addition, OKN elicited by temporalward stimulation of the non-deprived eye tended to be weaker in comparison to nasalward stimulation of that eye. A bilateral cortical lesion severely disrupted OKN behavior through the non-deprived eye but left OKN through the deprived eye relatively unaffected, with the result that the marked interocular differences in OKN that were present presurgically disappeared. During the recovery period following this lesion, there was a small gradual improvement in OKN through both eyes, so that OKN performance through the deprived eye ultimately exceeded that observed presurgically . Unilateral cortical lesions had little effect on OKN through the deprived eye, but they produced substantial changes in OKN through the non-deprived eye. Both the immediate effects of cortical lesions, and the patterns of recovery observed following these lesions, in many ways resemble those observed when normally reared cats are subjected to similar lesions. These behavioral experiments indicate that while subcortical OKN pathways are spared from the effects of long-term monocular deprivation, cortical pathways mediating OKN through the deprived eye are severely disrupted.

The sensitive period for strabismus in the kitten

Abstract The ocular dominance of single units in the striate cortex was assessed in normal kittens and in kittens exposed to either 2 days or 2 weeks of divergent strabismus at various times during rearing. The data indicate that the sensitive period for disrupting cortical binocularity by means of visual axis misalignment is similar to that for monocular deprivation. This result suggests that there is just one sensitive period for the development of cortical binocularity.

Distribution of visual callosal neurons in normal and strabismic cats.

It has been suggested that synchronous activation of cortical loci in the two cerebral hemispheres during development leads to the stabilization of juvenile callosal connections in some areas of the visual cortex. One way in which loci in opposite hemispheres can be synchronously activated is if they receive signals generated by the same stimulus viewed through different eyes. These ideas lead to the prediction that shifts in the cortical representation of the visual field caused by misalignment of the visual axes (strabismus) should change the width of the callosal zone in the striate cortex.