In an accompanying project concerned with the cerebral representation of the isolation call, it was found that bilateral ablations of the midline frontal cortex did not result in definitive retrograde degeneration in the thalamus of squirrel monkeys. The lack of such degeneration has been classically recognized in rhesus monkeys. In ongoing studies of the differential effects of ablations of the frontal midline neocortex and limbic cortex it is of basic importance to clarify the question in regard to afferent connections from the thalamus. Application of an improved technique employing wheat germ agglutinin conjugates to horseradish peroxidase (WGA-HRP) is being used for this purpose. Thus far, application of WGA-HRP to the pregenual and subcallosal limbic cortex has been found to result in conspicuous labeling in the rostral parts of N. anterior ventralis et medialis, N. centralis medialis; N. reuniens; N. ventralis anterior; N. ventralis lateralis medialis; N. paraventricularis; the N. parataenialis and N. centralis superior lateralis, together with the underlying part of N. medialis dorsalis; parts of N. parafascicularis and N. centralis lateralis; the medial protrusion of N. pulvinar medialis; and N. limitans. The several sites of extrathalamic labeling are given in the full report. Considered in the light of experimental and clinical data, the thalamic findings suggest a link-up of frontal lobe and striopallidonigral mechanisms implicated in both the affect and expression of crying and laughter.
