Thalamic projection to frontal cortex in man.

The object of this communication is to report the present position at the Maudsley laboratory of research on the projection of nerve cells of the human thalamus on to frontal cortex. Previous, more tentative, reports on this topic were published by Meyer, Beck, and McLardy in 1947 and by Meyer, McLardy, and Beck in 1948. The main material used consisted of 54 cerebral hemispheres with varied leucotomy lesions. A few cases of traumatic and of vascular damage to frontal cortex were also employed. Cortical areas involved in the primary lesions were correlated with the position of retrograde nerve cell degeneration and glial proliferation observed in Nissl-stained serial sections of the thalamus. For the sake of clarity only Brodmann's cytoarchitectural nomenclature is employed in the thalamic diagrams, but the relevant homologues in von Economo's nomenclatures are given in Fig. 1 (a). The main results which have emerged from this study may be summarized as follows. The whole of the dorsomedial nucleus projects to the granular frontal cortex, with the exception of its most dorso-posterior portion (i.e., the portion left blank in Fig. 1 (d)), its most rostral tip, and probably a portion of the pars magnocellularis on its medial border. These three portions appear to be devoid of frontal connexion. Those nerve cells of the pars magnoceUularis of the dorsomedial nucleus which have definite cortical connexions project to granular cortex within the medial half of the orbital region, i.e., essentially to Brodmann's area 11. The pars parvocellularis projects to the remaining granular frontal cortex in the manner indicated by the Brodmann numerals in Figs. I (b) to 1 (d). It is possible that fibres projecting to the medial half of the orbital cortex travel outside the internal capsule, ventral to the striatum. There is an antero-posterior axial organization, in that the more rostral cells of the pars parvocellularis are related to the more rostral portions of its cortical projection field, the more caudal to the more caudal; also a general coronal circum-