DRIVE AND MOTIVATION 



<5 2 3 



later consummation or performance of a learned re- 

 sponse involving very little consummation. They 

 were also able to show that injection of fluid directly 

 into the stomach could be used as the reward to pro- 

 mote the learning of a simple maze, but that allowing 

 animals to drink milk or water by mouth was an even 

 more effective reward. 



In another study, modeled after Andersson's work 

 on the goat, this same laboratory was able to confirm 

 the finding that intraventricular injections of minute 

 quantities of hypertonic solutions increased the thirst 

 of cats, and to demonstrate further that injections of 

 water and hypotonic solutions led to decreased thirst. 

 This result turned up with the use of a consummatory 

 response as a measure and also with the use of a 

 learned response in which the animal worked for rela- 

 tively few opportunities to drink (ioi). In similar 

 studies with food, there has been some question as to 

 whether stimulating the medial hypothalamus elec- 

 trically elicits hunger motivation or merely evokes re- 

 flexes of seizing, chewing and swallowing, for stimu- 

 lated animals sometimes seize and chew nonedible 

 objects. That there is an actual increase in motivation 

 upon stimulation of the ventromedial hypothalamus, 

 however, is confirmed by the fact that following 

 stimulation these animals will press a bar many times 

 to get an occasional tiny bit of food, even though they 

 are otherwise satiated (ioi). 



Obviously, agreement among the various measures 

 of motivation in determining the effects of a physio- 

 logical variable strengthens the conclusions we can 

 draw about the mechanism of motivation. Disagree- 

 ment may mean one of two things, however: that 

 there is interference with something specific to the 

 behavior invoked in the affected measure, not neces- 

 sarily of a motivational nature, or that there are dif- 

 ferent facets of motivation measured by the different 

 tests and subserved by somewhat different physio- 

 logical mechanisms. Clearly, it will be profitable to 

 extend the measures of motivation used in physiologi- 

 cal studies to include techniques that are not solely 

 dependent upon consummation. 



The third and most striking kind of experiment in- 

 volving learning is the use of electrical stimulation of 

 the brain to serve the function of a reinforcement, 

 much like a food reward for a hungry animal, or 

 much in the way that escape or avoidance of an elec- 

 tric shock reinforces a new response. The first study 

 along these lines was by Delgado et al. (50). By im- 

 planting electrodes in the vicinity of the medial 

 lemniscus and posteroventral nucleus of the thalamus, 

 these workers were able to elicit clear negative moti- 



vation in cats of the sort observed upon administering 

 electric shocks to the feet. They reported four major 

 results, a) Cats learned to rotate a wheel to turn off 

 this central stimulation, b) They learned to respond 

 to an auditory signal by turning the wheel in order to 

 avoid the stimulation that had alwavs followed the 

 signal previously, c) They learned to escape immedi- 

 ately when placed in a compartment in which they 

 had received central stimulation. d) Central stimula- 

 tion administered at the time of feeding inhibited 

 eating for long periods of time, despite strong hunger. 

 Thus by stimulation in the vicinity of the pain path- 

 ways centrally, these workers were able to elicit strong 

 negative motivation, sufficient to reinforce a variety 

 of kinds of learning. 



On the positive reinforcement side, Olds & Milner 

 (1 14) have reported that rats will work in order to be 

 Stimulated at a number of points within the brain. If 

 an electrode is chronically implanted in the septal 

 area or the mamillothalamic tract and activated every 

 time after the rat presses a lever, the animal will 

 change its rate of pressing the lever from several times 

 an hour to as high as almost 750 times an hour. Self- 

 stimulation of the cingulate gives similar but less 

 marked results, while corpus callosum, caudate and 

 hippocampal stimulation yielded no effect. Stimula- 

 tion of the tegmentum was equivocal, and medial 

 lemniscus and medial geniculate stimulation, if an) 

 thing, produced avoidance of the lever. 



follow in» this sainc procedure of sell-stimulation 

 reinforcement with rats and cats, Sidman et al. (141) 

 used the technique of administering stimulations only 

 after certain lever pressings. When the schedule of 

 stimulations called for activation of the implanted 

 electrode at irregular intervals of time, averaging 

 id sec, low rates of responding were obtained. When 

 the schedule called for seven pressings for each stimu- 

 lation, the rate of responding was very high. These 

 results were typical of those ol it. lined with such varia- 

 ble-interval and fixed-ratio schedules of reinforcement 

 with food or water as the rewards. Thus, it appears 

 that under appropriate experimental conditions, 

 stimulation of the brain can be rewarding and can 

 reinforce the performance of a learned response in 

 much the same manner as food and water do for the 

 hungry or thirsty animal. 



In this work, Sidman et al. found stimulation of the 

 septal area most effective for the rat and the caudate 

 for the cat. In a later study on the rat, Olds (113) 

 concluded that the stimulation of the amygdaloid 

 complex and the anterior hypothalamus were as effec- 

 tive as stimulation of the septal area in yielding high 



