An experimental-anatomical study on the cortical projections of the dorsomedial nucleus of the thalamus in the cat

The present study attempts to clarify the cortical projection of the dorsomedial thalamic nucleus with the use of the Nauta-Gygax and Fink-Heimer methods. The dorsomedial nucleus is composed of dorsal, medial, lateral and ventral parts. Its cortical projection areas are the lateral prorean cortex and the lower bank of the presylvian sulcus, as well as the medial frontal cortex extending from the prorean gyrus to the cortical part just ventral to area 6 dorsally and to the rostral portion of the anterior limbic region caudally. Although there is an apparent overlap between the cortical projections from the different parts of the dorsomedial nucleus, the dorsomedial nucleus projects to the frontal cortex in a topical manner anteroposteriorly. In cases with lesions in the medial and dorsal parts, marked cortical degeneration is found in the medial frontal cortex and the ventral portion of the lateral prorean cortex, whereas in cases with lesions in the lateral and ventral parts marked degeneration is detected in the dorsal portion of the lateral prorean cortex and the lower bank of the presylvian sulcus. This suggests that there is a mediolateral organization in the cortical projection of the dorsomedial nucleus. The boundary between the marked projection areas of the medial (and dorsal) and the lateral (and ventral) parts may be represented by the anterior rhinal sulcus and its rostral extension. No evidence of a topical organization in the dorsoventral direction is found in the cortical projections of the dorsomedial nucleus. In addition, it is difficult to determine to which area of the frontal cortex the dorsal or ventral part projects. However, the dorsal part tends to send fibers largely to the anteroinferior margin of the frontal lobe. Each part of the dorsomedial nucleus may be said to have both localized and diffuse projections to the frontal cortex. That is, if the lesion is not so small, the localized lesions anywhere in each part of the dorsomedial nucleus tend to cause diffuse scattered degeneration in almost the whole extent of the cortical projection area of the dorsomedial nucleus, in addition to dense localized degeneration which varies with the site of the lesion