THE INTRINSIC SYSTEMS OF THE FOREBRAIN 



■339 



mechanisms in tlic carotid Ijody and brain stem (87). 

 Food deprivation, as in starvation, is insufficient per 

 se to increase appetite. Long-term deprivation of 

 mating leads as often to continence as to frustration — 

 these examples suffice to suggest that physiological 

 need is not invariably produced by deprivation. And, 

 of course, the converse also holds, in that 'need' (as 

 measured by the rate or amount of movement related 

 to an outcome) may actually increase when recm- 

 rently 'satisfied' (77). 



On the other hand, the more complete specification 

 that takes into account the reciprocally related re- 

 curring changes in the distribution of excitability 

 and rest is supported by physiological fact. The 

 electrical activity of totally isolated neural tissue is 

 cyclical (7). The period of cyclical activity can be 

 specified and any changes imposed on the normal 

 periodicity can be described. The advantages of such 

 description are : the 'amount of excitability' is not con- 

 fused with 'amount of energy'; a particular event may 

 increase excitability at one time, and may decrease it 

 at another; thus, the effect of an outcome of an action 

 is conceived to depend on the phase of the excitability 

 cycle at the moment of action. The disposition of an 

 organism is therefore a basic determinant of inten- 

 tional beha\ior. Dispositions are conceived to be de- 

 pendent on changes in the periods of neural excita- 

 bility cycles. 



A'fechanism of Expectatinn 



By analogy with the model describing the functions 

 of the extrinsic and posterior intrinsic mechanisms, 

 the proposal of a model of the frontal intrinsic and 

 medioijasal forebrain mechanisms begins with a state- 

 ment of the variety of transformations of descriptions 

 of the outcome under which l^ehavior remains in- 

 variant. Following extensive bilateral resections of the 

 mediobasal systems, behavior remains in\ariant over 

 a wide variety of transformations of outcome, for 

 example, even gross changes in the amount of food 

 deprivation minimallv alter rate of response to food 



(147)- 



Frontal intrinsic sector lesions affect intentional 

 behavior that remains invariant only under the more 

 restricted ranges of transformations of the outcome, 

 transformations whicii in controls can be shown to 

 affect the distribution of intentional respon.ses. In the 

 extreme, unique distributions, such as those measured 

 by indifference functions, would be most affected by 

 such lesions. 



L'nique distributions can occur onlv when Ijoth the 



units of intention and their referent have been fixed. 

 Difficulties in defining such units and their referent 

 stem from the cyclical variations which describe the 

 dispositions of organisms — difficulties already di- 

 cussed from the neurobehavioral standpoint. The 

 formal device 'mathematical expectation,' which is so 

 usefully applied to the analysis of the effects of frontal 

 intrinsic sector lesions, is designed to overcome the 

 difliculties encountered in analyzing the solution of 

 proi:)lems characterized by cyclic phenomena (141). 

 This device, based on combinatorial (equilibratory) 

 and set theoretical methods, meets the difficulties by 

 the suggestion that the solution of such problems is 

 described, not by the single elements (outcomes) that 

 define the problem, but by sets (and subsets) of such 

 elements. Unfortunately, the mathematics falls some- 

 what short of accoiTiplishment in this area and only 

 some rudimentary approaches to the task are possible 

 at this time (142). 



Nevertheless, the relevance of the device, mathe- 

 matical expectation, in the analysis of the results of 

 the multiple-object and constant-interval experiments, 

 suggests the formal model of the frontal intrinsic 

 mechanism. This model conceives the frontal intrinsic 

 mechanism to partition the events in the mediobasal 

 forebrain systems, dispositional events that determine 

 the effect of outcome variables. Partitioning results in 

 distributions of intentions, intentions determined by 

 the elements of the subset resulting from the partition. 

 The frontal intrinsic mechanism is thus conceived to 

 provide both referent and units although not the 

 elements that specifv intentional behavior. The effect 

 of continued frontal intrinsic sector activity will, 

 according to this model, result in an increasingly com- 

 plex sequence of distributions of intentions which in 

 turn allow more and more precise specifications of 

 intent that can be conveved for any given outcome. 

 As a result, the organism's intentional behavior re- 

 mains invariant under a progressively narrower range 

 of systems of transformations of outcomes — intentions 

 become more precise. 



The programing of the activities of the frontal 

 intrinsic sector remains in question. Some things are 

 clear, however. The advantage of the model is that 

 the program is not composed by the events upon 

 which the program operates. Thus, as in the case of 

 the posterior intrinsic mechanisms, storage of en- 

 coded programs is demanded — not storage of an ever- 

 increasing number of discrete preferences. In this 

 formulation, the frontal intrinsic sector is conceived 

 as a programing mechanism that maps intentions — 

 a conception that is in accord both with experimental 



