Limbic Nuclei of Thalamus and Connections of Limbic Cortex

Introduction Comparative studies of the thalami of various mammals,²including marsupials,⁵the rabbit,²⁸,⁶¹,⁸⁰rodents,²⁵,²⁹,³³the sheep,⁶²carnivores,³⁰,⁶⁰,⁷⁹and primates,¹⁰,¹⁵,⁷²⁻⁷⁵demonstrate a progressive phylogenetic enlargement and differentiation of nucleus medialis dorsalis (MD), in parallel with the development and elaboration of the frontal lobes (ie, opercularization of insula). In man, MD is the largest member of the internal segment of the dorsal thalamus; the anterior, lateral, and inferior borders of the nucleus are clearly delineated by the internal medullary lamina in myelin-stained sections and are visible even in unstained slices of the fresh brain. The precise cytoarchitectonic differentiation of MD from neighboring nuclei—the midline and intralaminar nuclei and the medial pulvinar—is difficult, however, at several points.⁵⁴,⁶⁵ A number of authors (Clark,¹⁰Walker,⁷²⁻⁷⁵Sheps,⁶⁵Toncray and Krieg,⁶⁹Olszewski,⁵⁴Dekaban¹⁸) have recognized in primates two or three and sometimes four