DRIVE AND MOTIVATION 



General Activity 



The most general measure of motivation is to re- 

 cord gross bodily activity. This measure is simply a 

 quantitative record of the intensity of behavior and 

 as such serves primarily as an index of drive. While 

 many factors influence bodily activity, and not every 

 change in activity is a change in drive, it is nonethe- 

 less possible under appropriate experimental condi- 

 tions to show that changes in activity do reflect 

 changes in drive. 



Two somewhat different kinds of general activity 

 have been recorded. The one most often used is gross 

 locomotor activity. This is the measure obtained 

 when a rat runs in a rotating drum or activity wheel 

 (no), or when an animal is tethered to a counting 

 device (84). The second measure is of restless activity, 

 recorded in a tambour-mounted (125) or spring- 

 suspended cage (73), the tilting cage (26), or the cage 

 divided by a photoelectric beam (142), where small 

 as well as large movements may activate the recording 

 system. In addition, there are several other kinds of 

 activitv which can be recorded and which have been 

 seen particularly following certain brain lesions: 

 stereotyped pacing back and forth (133), forced 

 circling (78), forced following of visual stimuli (77, 

 144) and obstinate progression (7). 



A number of studies show a systematic relationship 

 between changes in drive and changes in activity. 

 In the female rat, for example, activity increases 

 during estrus, when estrogen levels and sexual re- 

 ceptivity are high, and decreases during diestrus ( 162). 

 Where a rat is deprived of food or water or both, or 

 of certain vitamins, activity increases steadily as dep- 

 rivation proceeds, reaching a peak and then falling 

 off as the animal becomes physically impaired (23, 

 161). This peak may be as much as five times basal 

 activity and is reached alter 5 days of food or water 

 deprivation, 2 days of both food and water depriva- 

 tion, and 10 days of vitamin deprivation. That the 

 factor of physical impairment may be specific to the 

 locomotor activity measure is suggested by the finding 

 that gonadectomy reduces running activitv by go 

 per cent (72), while it results in only a 10 per cent 

 decline in restless activity (73). 



In addition to physical impairment, there are other 

 variables, not necessarily related to drive, which also 

 influence activitv. In a number of different experi- 

 ments, it has been found that: a) activitv is related 

 to daily light-dark cycles, the rat, for example, dis- 

 playing most of its activitv at night (37); b) activitv 

 is high in low environmental temperatures and low in 



high temperatures (38, 39); and c) it is possible to 

 breed selectively for activity (134). 



Accordingly, while the association between activitv 

 and drive is an empirical fact, successful use of gross 

 bodily activity as an index of drive depends upon care- 

 ful control of conditions of measurement. This is 

 particularly true because learning and other sources 

 of individual differences make the activity measures 

 very variable. For example, it may take some animals 

 from 10 to 25 days of constant opportunity to run in 

 wheels before they run at all, and it may be over a 

 month before animals kept on a restricted feeding 

 schedule reach a stable base line of daily running 

 (124). Furthermore, these individual differences may 

 be quite large in absolute magnitude, some rats 

 running over 20,000 revolutions a day (over 10 

 miles) while others may never exceed 200 revolutions 

 a day. 



Despite all these shortcomings, we may conclude 

 that gross bodily activitv is a function of the amount 

 of drive and that, under appropriately controlled con- 

 ditions, increases in drive arc reflected in increases in 

 activitv up to the point where the animal is physically 

 impaired. 



Consummaiory Behavior 



The most commonly used measure of motivation 

 in physiological studies is the goal-directed consum- 

 mately response, idealized in the examples of lood 

 ingestion and water intake. In these two instances, the 

 experimental procedure is to measure the amount 

 consumed in some standard test situation where the 

 animal is, ideally, but not necessarily actually moti- 

 vated in just one way (e.g. deprived of water) and is 

 limited in its choice of responses to one goal (watei 

 In addition, the animal is usually given the oppor- 

 tunity to habituate to the test situation cmotionallv 

 and to adapt to the physical and temporal circum- 

 stances of testing. Under such conditions, it has been 

 shown that the amount of water ingested is a function 

 of the amount of deprivation. Rats, for example, will 

 drink more and more water following longer and 

 longer deprivations up to the 8th day of deprivation 

 when they will succumb (152). No in-between point 

 of physical impairment where water intake falls off 

 alter reaching a peak has been reported as in the case 

 of other measures of motivation, like running activity 

 or performance in the obstruction box (see below I. 



Detailed analysis of the course of water intake gives 

 further insight into thirst motivation and shows the 

 complexity of even simple consummatory response 



