Although the functional significance of the midprincipalis region is well known, the afferent and efferent connections of this zone, in comparison tot the anterior and posterior portions of the cortex lining the princ...
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Although the functional significance of the midprincipalis region is well known, the afferent and efferent connections of this zone, in comparison tot the anterior and posterior portions of the cortex lining the principal sulcus, are poorly understood. In 3 rhesus monkeys the retrograde tracer HRP [horseradish peroxidase] and the anterograde tracers, 3H- proline, lysine and leucine, were injected into the sulcal cortex lining the principal sulcus. The cortex forming the banks of the principal sulcus was divided into anterior, middle and posterior sectors with 1 animal used for each zone. As expected from previous studies, the heaviest afferents to the cortex forming the principal sulcus were from the parvocellular portions of the medial dorsal nucleus. The medial pulvinar nucleus and the nucleus limitans projected to only the anterior and posterior portions of the cortex lining the principal sulcus. Projections were seen to all 3 sectors from the anterior, midline, intralaminar and lateral thalamic nuclei. Although cells were seen in the hypothalamus following injections in all 3 sectors of the cortex lining the principal sulcus, the heaviest hypothalamic projections were noted after injections into the mid-sector of the cortex. These HRP-positive cells were in the dorsal and lateral hypothalamic area, dorsal medial nucleus and in the lateral mammillary nucleus. These findings link the midprincipalis region with the prefrontolimbic circuit, and suggest that the midprincipalis region, n. [nucleus] medialis dorsalis, the mammillary bodies and perhaps the cingulate gyrus constitute part of an anatomical circuit concerned with memory processes.
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