An Experimental-Anatomical Study on the Efferent Connections of the Dorsomedial Thalamic Nucleus in the Cat

Localized electrolytic lesions were placed stereotaxically in the dorsomedial thalamic nucleus of the cat, and the ensuing degeneration was traced in serial sections impregnated by the Nauta-Gygax method. The major conclusions are as follows: 1. In the present study the dorsomedial nucleus is divided into a medial and a lateral part, the latter being composed of dorsal, lateral and ventral parts in a narrow sense. 2. The dorsomedial nucleus is connected with the neighboring thalamic nuclei, though some intrinsic fibers spread within the nucleus. The medial part projects to the lateral central nucleus, paracentral nucleus, anterior and posterior paraventricular nuclei, rhomboid nucleus and medial ventral nucleus. The lateral part projects to the parafascicular nucleus, dorsal and posterior lateral nuclei, submedial nucleus and lateral ventral nucleus, in addition to the intralaminar nuclei. Besides, the dorsomedial nucleus sends fibers to the anteriormost part of the reticular nucleus. Its caudal part gives off a few fibers to the posteromedial ventral nucleus and the medial pulvinar nucleus. 3. In addition, the dorsomedial nucleus projects to some subcortical centers, such as the lateral preoptic and lateral hypothalamic nuclei, olfactory tubercle, nucleus of the diagonal band, claustrum and entopeduncular nucleus. In some cases it sends a few fibers to the anterior extremity of the amygdaloid complex, but does not appear to project to the caudate nucleus, putamen and globus pallidus. 4. The dorsomedial nucleus projects diffusely to the medial cortex of the frontal lobe and the lateral cortex of the proreal gyrus. However, the medial part of the nucleus sends abundant fibers to the medial cortex of the frontal lobe, while the lateral part of the nucleus projects profusely to the lateral cortex of the proreal gyrus. On the other hand, the anterior part of the dorsomedial nucleus projects predominantly to the anterior part of the frontal cortex, and the posterior part of the nucleus to the posterior part of the frontal cortex. These data indicate that the essential cortical projection of the dorsomedial nucleus is organized in both the mediolateral and anteroposterior dimensions, though any part of the dorsomedial nucleus can project diffusely to the entire frontal cortex. 5. In cases with lesions in the lateral part of the dorsomedial nucleus, some degenerated fibers in the cortex of the proreal gyrus tend to spread dorsolaterally beyond the presylvian sulcus into the cortex of the anterior sigmoid, coronal and orbital gyri