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HANDBCMJK OF PHYSIOLOGY 



NEUROPHYSIOLOOY II 



FIG. J. Schematic representation of the 

 projections from the dorsal thalamus to the 

 cerebral cortex in the monkey. Ihe lower halj 

 of the ligure diagrams the thalamus, the 

 slraighl edg^e representing the mid-line; thi- 

 upper halj of the figure shows a lateral and 

 inediobasal view of the cerebral hemispheres. 

 The hrimd black band in the thalamic diagram 

 indicates the division between an internal core 

 which receives a nonspecific diffuse input and 

 an external portion which receives the mo- 

 dality-specific discrete projection tracts. Tin 

 slippled and crosshatchcd portions represent the 

 intrinsic systems: the medial nucleus of the 

 internal core and its projections to the anttro- 

 frontal cortex, the posterior nuclear group of 

 the external portion of the thalamus and its 

 projections to the parietotemporooccipital 

 cortex. The boundaries of the cortical sectors 

 of the intrinsic systems are not sharp and as 

 yet not precisely defined — thus, this diagram 

 is to be read as a tentative approximation, 

 based on currently available evidence. /•, 

 frontal; R, rolandic; P, parietal; T, temporal; 

 O, occipital; A, anterior; C, central; M, 

 medial; V, ventral; G, geniculate; F, posterior. 



THALAMOCORTICAL 

 RELATIONS (MONKtY) 



foreljrain and includes the basal g;ans;lia. Specifically, 

 the ventral group of the external portion of the dorsal 

 thalamus projects to the dorsolateral cortex of the 

 frontal and parietal lobes (15, 144); the geniculate 

 groups, to the lateral portion of the temporal and the 

 posterior portion of the occipital lobe (144); the 

 posterior nuclear group, to the remaining cortex 

 of the parietotemporopreoccipital (P.T.O.) convexity 

 (•o, 15). 



Within the internal core (figs, i, 2), the medial 

 nuclei project to the anterofrontal cortex (or orbito- 

 frontal, as it has been called in subprimate mam- 

 mals) (86, 1 12, 123, 144). The anterior and the central 

 nuclei project to the medial and basal forelirain struc- 

 tures, the anterior nuclei to the cinguiate areas on 

 the medial surface of the frontal and parietal lobes 

 (73, 86, 106, 113, 122, 125, 146); the central nuclei 

 project (j, 20, 98, 105, III, 124) to the anterior 

 rhinencephalic and closely related juxtallocortical 

 areas and basal ganglia [the second rhinencephalic 

 system as defined by Pribram & Kruger (i 14)]. 



In summary, an intrinsic nuclear group and its 

 projections is described for each of the major thalamic 

 subdivisions : a posterior intrinsic system, related to 

 the external portion of the thalamus and the dorso- 

 lateroposterior cerebral convexity; a frontal intrinsic 

 system, related to the internal core of the thalamus 



and the frontomediobasal areas of the cerebral 

 hemispheres. 



NEUROBEH.WIOR.AL .\N.^LYSIS OF POSTERIOR 

 INTRINSIC SYSTEM 



As already noted, the forebrain may conveniently 

 be divided into two major portions, a dorsolatero- 

 posterior and an anteromediobasal. In primates each 

 of these major portions contains intrinsic sectors: 

 posterior intrinsic sectors (the classical sensory associ- 

 ation areas) (108), and a frontal intrinsic sector (the 

 classical frontal as.sociation area) (110). Neurobe- 

 havioral experiments performed during the past 25 

 years have shown these intrinsic sectors to be especially 

 related to problem-solving processes (51, 107). The 

 aim of this, and of the following sections, is to specify 

 in detail this relationship. 



An Experiment 



A. modified Wisconsin General Testing Apparatus 

 (49) is used to test 1 2 rhesus monkeys in the solution 

 of a complex problem. The monkeys are divided into 

 three groups, two operated and one control, each con- 

 taining four animals. The animals in one operated 



