THE INTRINSIC SYSTEMS OF THE FOREBRAIN 



1333 



to the functions of the intrinsic sectors, but the view- 

 points share the proposition that the intrinsic sectors 

 do not function independently of the extrinsic. The 

 common difficulty has been the conceptualization of 

 this interdependence between intrinsic and extrinsic 

 systems in terms other than the transcortical 'reflex' 

 model — a model which became less cogent with each 

 new experiment. 



Pariitioiniig 0] Sets 



There is an alternative concept which meets the 

 objections levied against the transcortical 'reflex' yet 

 accounts for currently available data. The relation- 

 ship between intrinsic and extrinsic systems can be 

 attributed to convergence of efferents from the two 

 systems at a subcortical locus, rather than to specific 

 afferents from the extrinsic to the intrinsic cortex. 

 Some evidence supporting this notion is already 

 available. Data obtained by \Vhitlock & Nauta (150), 

 using silver staining techniques, show that l)Oth the 

 intrinsic and the extrinsic sectors implicated in vision 

 bv neuropsychological experiments are eff^erently con- 

 nected with the superior colliculus. On the other 

 hand, lesions of the intrinsic thalamic nuclei fail to 

 interfere with difTerentiative iaehavior (13, 102). Thus, 

 the specific effects in behavior of the intrinsic systems 

 are explained on the basis of efferents to a subcortically 

 located neural mechanism that has specific functions. 

 These efferents can be conceived to partition the 

 afferent activity that results in the events in the 

 extrinsic sectors, events initiated ijy and corresponding 

 to the input variables. Partitioning determines the 

 e.xtent of tiic range of possibilities to which an element 

 ora set of elements can be assigned. Partitioning results 

 in patterns of information, information given by the 

 elements of the subsets resulting from the partition 

 {140). The posterior intrinsic sector mechanism is thus 

 conceived to provide both referent and units, though 

 not the elements to be specified. The effect of con- 

 tinued intrinsic sector activity will, according to this 

 model, result in a sequence of patterns of information 

 (partitions) of increasing complexity, which in turn 

 allow more and more precise specification of par- 

 ticular elements in the set (or subsets) of events oc- 

 curring in the extrinsic systems. Thus, through con- 

 tinued posterior intrinsic sector activity, more and 

 more information can be conveyed by any given in- 

 put. As a result, the organism's difTerentiative be- 

 havior remains invariant under a progressively nar- 

 rower range of systems of transformation of the input — 

 difTerentiations become more 'absolute.' 



The programing of the activities of the posterior 

 intrinsic sectors remains in question. Some things are 

 clear, however. The advantage of this model is that 

 the program is not composed by the events upon 

 which the program operates. In this respect the model 

 is in accord with neural and neurobehavioral facts 

 (108). Other models, whether associationistic or 

 match-mismatch (6), demand the storage of an ever 

 increasing number of 'bits' of information. The evi- 

 dence is overwhelmingly against the presence in the 

 nervous system of such minutely specific engrams 

 (71). In the model here presented, engrams consist of 

 encoded programs. These operate on the neural 

 events that are initiated by the input, transforming 

 them into other neural events which can lead to an 

 ever increasingly finer, that is, a more appropriate, 

 difl["erentlal response (42, 148). In this formulation 

 the posterior intrinsic sectors are conceived as pro- 

 graming mechanisms that function to partition events 

 initiated by the input, not as the loci of association 

 of such events, nor as the loci of storage of an ever 

 increasing number of minutely specific engrams. 



NEUROBEH.'ilVIOR.'>iL .\N.ALVSIS OF FRONT.AL 

 INTRINSIC SYSTEM 



The mechanism by whicii the posterior intrinsic 

 sectors is conceived to affect differential behavior 

 finds a parallel in the mechanism by which the frontal 

 intrinsic sector can affect intentional behavior. The 

 demonstration of this parallel is most effectively 

 initiated by some definitions that allow further 

 analy.ses of the data obtained in the multiple object 

 discrimination experiment. 



Somr Definitions 



Behavior theory often begins with the statement 

 that a response is a function of certain organismic 

 variables (such as drive or habit) and of a 'stimulus' 

 which is conceived as some environmental event or 

 constellation of environmental events. This classical 

 behaviorist position has been challenged bv those 

 primarily interested in psychophysical and perceptual 

 problems (3, 135); these investigators are concerned 

 with the more precise specification of the category 

 'stimulus' as including 'distal' (e.g. environmental) 

 and 'proximal' (organismic, i.e. receptor) events. This 

 concern must be shared by the neuropsychologist 

 who is interested in the relationship between central 

 processes and behavior since complex interactions 



