THE INTRINSIC SYSTEMS OF THE FOREBRAIN 



1325 



E tec trophy tlology (e.g. 

 Magoun, 1950; Staril, 



etol., 1951) 

 Sliver stoin [Morin, 



et ol., 1951) 



Comporative hi stomorphology 

 (e.g. Kappers, Huber & Crosby, 

 1936; Rose 8. Woolsey, 1949) 



Retrograde thalamic degenerotion 

 after cortical removoU, Monkey, 

 (e.g. Walker, 1938; Chow, 1950, 

 Chow 5. Pribrom, 1956, Pribram 

 etal., 1953) 



Cytoarchltecture K Strychnine 

 neuronogrophy (e.9. v. Benin 

 ?. 3atley, 1947; Bailey, 

 v. Bonin ?. McCulloch, 1950; 

 MocLeon 5, Pribram, 1953, 

 Pribram K MacLean, 1953) 



'Posterior « 



Ventral* 



Mode-Specific 

 Discrete Input 



Geniculote a 



External Portion 



• n. loteralis posterior - 

 ■•n. pulvinaris ^— ^^-^^ 



-Posterior parietal cortex- 

 -Posterior parietal ?, temporol cor- 

 tex 8. anterior occipital cortex 



ventrolis anterior — 

 ventralis laterolis- 

 ■ n. ventralis posterior- 



( basolis^ 



■■n. geniculotus medialis- 

 -n. geniculotus lateralis* 



-Dorsal frontol cortex 

 — P recent ro I cortex 

 -Rolondic cortex 



.Posterior supratemporal plane^ 



S, posterior insular cortex 

 -Striate occipital cortex 



Eugronular isocoftex of the 

 parietol, temporal i occi- 

 pitol lobes (the posterior 

 "association" cortex) 



lAg'onular, dysgronular 

 li konioisocortex 



Non-Specific 

 Diffuse Input 



Internal Core 



• n. anterior dofsolis 

 -n. anterior ventralis ■ 

 ^n. anterior mediolis^^^— 



.^nuclei of the midline 



(e.g. n. reuniens) 

 -jntrolaminor nuclei (e.g.- 

 n. centralis mediolis) 



* n. centromedianum ^^^^— 



-Retrosplenial cingulate cortex 

 -Posterior cingulate cortex 

 • Anterior cingulate cortex 



-Subcallosal 8, medial orbital corte 



-Orbitofronto-insulo-temooral 



cortex 5, basol gonglia (caudotej 

 — Basal ganglia (putamen) 



*Medial- 



n. mediolis dorsalis. 



.Anterofrontol cortex 



Alio- S. [uxtallocortex o^ 

 the limbic portions of the 

 hemispheres 8, closely 

 related subcortical fore- 

 brain structures 



Frontal eugronular 

 isocortex (the frontol 

 "association" cortex) 



FIG. 1. Diagram of the distinctions between an internal core and an external portion of the 

 forebrain. Examples of the techniques and particular studies invoked in making the classification 

 are given in the upper column. As in any such classification, its heuristic value should not obscure 

 its deficiencies. There is, of course, a multiplicity of forebrain systems, each of which partakes 

 to a greater or less extent of the characteristics defining the internal core and those defining the 

 external portion. In general, however, the nearer a system is to the central canal (or ventricular 

 system) of the central nervous system, the greater the number of its 'internal core" characteristics; 

 the further from the central canal, the greater the number of its 'externa! portion" characteristics. 

 Also, the interaction of these various systems must not be ignored; this scheme is a restricted analysis 

 and does not deal with such interactions. 



tion of the mesencephalon and, in addition, a probable 

 input from the anteromedial hypothalamus (95, 96).' 

 Thus the constancies of morphology in the mam- 

 malian thalamus reflect certain gross distinctions 

 which can be made in the types of afFerents to the fore- 

 brain. 



The other two nuclear groups, the posterior in the 



^ In this respect, the classification presented here differs 

 from that of Rose and Woolsey. These authors do not accept 

 the evidence from silver -stained preparations as indicating a 

 major extrathalamic, extratelencephalic input. Heuristically, 

 such evidence is accepted here. 



external portion and the medial in the internal core, 

 do not receive any such major extrathalamic aflferents 

 and, as noted above, are therefore classified as the 

 'intrinsic' nuclei of the thalamus (124). Important to 

 the argument presented here is the fact that an 

 intrinsic nucleus is assigned to each of the major 

 thalamic divisions (see fig. 2). 



The telencephalic projections of the external por- 

 tion of the dorsal thalamus terminate in the dorso- 

 lateral and posterior cortex (figs. 1,2). The termina- 

 tion of the telencephalic projections of the internal 

 core is in the frontal and mediol^asal portions of the 



