'VI 



il Wlilli K iK i il I'll 1 ! S .\ 



NEUROPHYSIOLOGY III 



rates of responding, while moderate rates were pro- 

 duced upon stimulation of the cingulate, hippocam- 

 pus, posterior hypothalamus and anterior thalamus. 

 The distinction between effective and ineffective 

 points, and rewarding and punishing [joints, however, 

 may not be simple. Miller and his colleagues (mi | 

 have reported that a single point may he positively 

 reinforcing in the sense that an animal will work to 

 have it stimulated, but it may also be negatively re- 

 inforcing, for the animal will escape from it if it has 

 the opportunity. 



From a purely behavioral point of view, it looks as 

 though direct stimulation of the brain should have 

 the same physiological effect as the various rewarding 

 consummatory responses that eventually lead to satia- 

 tion. This notion is supported by the fact that so many 

 of the effective points for self-stimu'ation reinforce- 

 ment arc in areas of the brain that are known to play 

 .in important role in motivation. However, we lack the 

 specific experimental information as yet to tell whether 

 the reinforcing effects are tantamount to transient 

 drive reductions or satiations of specific motivations 

 through appropriate activation of their specific 

 mechanisms; or whether these reinforcing effects are 

 not specific to any of the mechanisms of motivation, 

 but rather evidence for a general mechanism for 

 'pleasure' or, put more operationally, reinforcement. 

 Preliminary reports on human patients with elec- 

 trodes implanted in the septal area indicate "feelings 

 of comfort' upon stimulation (68). But it is too early 

 lo speculate beyond these general possibilities, for at 

 present there are too few facts at hand. 



CllNCI I'SIONS 



A number of conclusions can be derived from this 

 historical and experimental analysis of the physio- 

 logical basis of motivated behavior. 



It is possible to siud\ motivated behavior with ob- 

 jei tive methods and to make an operational analysis 

 of the factors important in i t^ control without resort 

 in ieleuliMjie.il and vitalistic concepts. 



This analysis indicates that various kinds ol moti- 

 vated behavior, like hunger, specific hungers, thirst, 

 se\, maternal behavior, emotion, sleep, etc., are under 

 the s.ime general kind of multifactor control, receiving 

 influences from the various sensor) avenues, the in- 

 lern.il environment and the central nervous system. 



An often neglected, but nevertheless important 

 factoi is learning, for previously neutral stimuli can, 

 through experience, come to contribute i<> the arousal 



and satiation of motivated behavior, and various new 

 instrumentalities and goals may be learned in the 

 execution of motivated behavior. 



The relative contribution of the various factors con- 

 trolling motivation and presumably the underlying 

 physiological mechanisms change in the course of 

 phylogeny. Judging mainly from the example of sexual 

 behavior, there is with ascending phylogenctic posi- 

 tion an increasing dependence upon sensory factors, 

 learning and the cerebral cortex, and a decreasing 

 dependence upon the internal environment. 



The behavioral analysis of motivated behavior 

 divides it into three main aspects: drive, the intensitv 

 of the arousal and maintenance of motivation; goal- 

 directed behavior, the enhanced perception of selected 

 stimuli in the environment and the selective execution 

 of a pattern of behavior in respect to them; and satia- 

 tion, the reduction of drive once the goal is sufficiently 

 attained. 



Experimental methods are available to measure 

 drive and satiation quantitatively and to specify, 

 in some cases, the choice and selection involved in 

 goal-directed behavior. The possibilities for the meas- 

 urement of motivation are greatly increased by the 

 learning of new drives, new goals and new instrumen- 

 talities for attaining goals. There are, however, two 

 important limitations in the present methodologies: 

 a) the various measures of motivation are not always 

 in good agreement, and b) there is too much depend- 

 ence at present upon simple measures of consumma- 

 tory response. 



Physiologically, drive appears to be a function of 

 the activitv ol a general excitatory mechanism having 

 ils major central control in the hypothalamus, and 

 satiation is a function of a similar inhibitory mecha- 

 nism, for increases and decreases in many kinds of 

 motivated behavior can be produced by ablation and 

 stimulation of restricted hypothalamic foci. There are 

 two serious limitations in the conclusions we can draw 

 about localization, however, a) We do not know, with 

 im\ anatomical precision, the Structures in the hypo- 

 thalamus which must be involved to produce these 

 changes in motivation, we do not even know whether 

 lesions and stimulations are effective because they 

 affect nuclei or liber tracts or both. /)) We do not 

 know whether a particular effective locus subserves 

 onlv one kind of motivation or several kinds, although 

 there is much evidence suggesting overlap of function 



within the hypothalamus. 



Central neur.il structures outside ol the hvpothala- 

 uuis also contribute cm italoiv and inhibitory inllu- 

 ences to the control of motivation as main ablation 



