Showing papers on "Rhinal sulcus published in 1984"

Laminar origin and septotemporal distribution of entorhinal and perirhinal projections to the hippocampus in the cat

Abstract: The projections of the entorhinal and perirhinal cortices to the hippocampus in the cat have been studied with retrograde and anterograde tracing techniques. Retrogradely transported tracers, which were injected at different levels along the septotemporal longitudinal hippocampal axis, result in labeled neurons in superficial entorhinal cortical layers II and III. Occasionally, labeled cells were also observed in the deepest entorhinal layer as well as in the superficial layers of the perirhinal area 35. It could further be shown that labeled neurons located superficially in the entorhinal cortex are topographically distributed in a lateromedial gradient, which corresponds to a septotemporal gradient along the longitudinal axis of the hippocampus. This topographical organization of the entorhinal-hippocampal projection system could be substantiated by the use of anterograde tracing of radioactively labeled amino acids. Injections in the entorhinal cortex produce labeled fibers in the hippocampus. Injections in the perirhinal area 35 result also in labeling over the hippocampus, whereas area 36 does not seem to distribute fibers to the hippocampus. As anticipated from the results of the retrograde tracing experiments, injections located laterally, in or close to the posterior rhinal sulcus, produce prominent labeling over the septal pole of the hippocampus, whereas progressively more medially located injections result in progressively more temporally located labeling. This topographical distribution of perforant path fibers along the septotemporal axis of the hippocampus, which is related to a lateromedial axis in the entorhinal cortex, has been observed following injections in the lateral entorhinal area (LEA) as well as in the medial entorhinal area (MEA). The present observations are discussed in regard of other connectional and putative functional differences between the septal and temporal hippocampus.

The architecture and some of the interconnections of the rat's amygdala and lateral periallocortex

Abstract: The connections between the cerebral cortex and amygdala were studied in the rat by means of silver degeneration techniques. To help define the sites of origin and termination of cortico-amygdaloid connections, the architecture of the cortex and the amygdala was studied in sections from normal brains stained for cells, fibers, acetylcholinesterase activity, and heavy metals (Timm staining). The amygdalopetal cortex on the dorsal and lateral surfaces of the rat brain is limited to a narrow strip of periallocortex that forms the dorsal wall and lip of the rhinal sulcus. Histochemical stains indicate that this cortex comprises several stages of cortical differentiation that are intermediate between the ventrally adjacent allocortices and the dorsally adjacent neocortices. The lateral periallocortex consists of two major divisions, the agranular insula (area 13) anteriorly, and a temporal agranular cortex (areas 35 and 36) posteriorly. The principal amygdaloid target for this cortex is the lateral nucleus. Anterior area 13 and posterior area 35 project to the anterior and posterior halves, respectively, of the medial division of this nucleus, while posterior area 13 and anterior area 35 projects to the lateral division of this nucleus. All divisions of periallocortex also send projections to a part of the putamen that surrounds the lateral half of the central nucleus. All of area 13 also sends efferents to the anterior part of the basal nucleus, while the anterior half of area 13 sends an additional projection to the central nucleus. Comparison of these data with those obtained in the cat and monkey suggests that a constant feature of eutherian brains is the existence of a subset of efferents from each of the four neocortical sensory systems that is routed so as to provide subcortical limbic structures with modality-specific information. The initial sequence in this sensorilimbic system consists of one or more modality-specific corticocortical relays that originate in the primary sensory cortices and terminate in one of four topographically adjacent, modality-specific areas of the insular and temporal cortices. These insular and temporal areas then each establish modality-specific connections within the amygdaloid complex. The final set of relays presumably comprises the connection that each of these amygdaloid areas makes with the autonomic and endocrine nuclei of the brain.

Sequential behavior after modified prefrontallesions in the rat

Abstract: Ablation of the “orbital” prefrontal area, which includes the dorsal bank of the rostral third of the rhinal sulcus and the ventral surface of the frontal pole, strongly impaired performance of a new task that required sequential manipulation of two different and spatially distant manipulanda. Performance of the same task was only mildly, but significantly, affected by dorsomedial prefrontallesions. The two groups did not significantly differ from sham-operated controls in the rate of barpressing for continuous reinforcement, in extinction of two operant responses, or in spontaneous alternation. Unexpectedly, the present variant of sequential behavior was more affected by the “orbital” prefrontallesion than by the lesions of the cortex, which, in the rat, combines the medial prefrontal cortex and anterior cingulate areas and has been considered to be involved in the sequencing of behavioral chains.