THE EFFECT OF ACTIVITY DEPRIVATION UPON EXPLORATORY BEHAVIOR

K. C. MONTGOMERY

Yale University

In previous papers (e.g., 3) the author hasadvanced the hypothesis that novel stimula-tion arouses the exploratory drive, which leadsto exploratory behavior. A commonly acceptedalternative hypothesis is that exploratory be-havior is motivated by the "general activitydrive," i.e., exploratory behavior is one formof "general activity."

Several lines of evidence suggest that thelatter hypothesis is invalid. Anderson (1)found no significant correlations between onemeasure of general activity and severalmeasures of exploratory behavior. The resultsof several experiments by the author (3, 4, 5)show that the amount of exploratory behaviorof rats decreases rapidly during a 10-min.period of exposure to a simple maze and thatit increases with size of maze. It seems un-likely both that the general activity drive de-creases in strength this rapidly and that itis a function of maze size. The same studiesreveal that exploratory behavior is largelyunder the control of, i.e., directed by, externalstimulation, a finding difficult to explain interms of the general activity drive alone. Arelated finding (5) is that the decrement inamount of exploratory behavior produced byexposure to one maze generalizes to othermazes, decreasing in magnitude as the similar-ity of the mazes decreases. Again, this is a factdifficult to account for on the basis of thegeneral activity drive.

The present experiment is designed toanswer this question: Does activity depriva-tion affect the amount, the relation to time,or the orderliness of the exploratory behaviorof rats in a simple maze? It provides a directtest of the two hypotheses stated above. Oneoperation that should increase the strengthof the general activity drive is deprivingnormally nourished animals of activity. How-ever, this operation should not affect thestrength of the exploratory drive because thelatter is aroused by external stimulation, notby factors internal to the organism. If theexploratory behavior of a group of activity-

deprived animals is measured after variousperiods of deprivation and compared with thatof a control group not so deprived, mutuallyincompatible predictions follow from the twohypotheses. (1) If exploratory behavior ismotivated by the general activity drive, thenas length of activity deprivation increases,exploratory behavior should (a) increase inamount during limited periods of explorationand (b) decrease in amount progressively lessrapidly during successive periods of explora-tion. (2) If it is motivated by the exploratorydrive, it should be relatively unaffected byactivity deprivation either in amount or inits relation to time. No differential predictionsabout the order characteristics of exploratorybehavior follow from these hypotheses.

METHOD

SubjectsThe 5's were 18 male albino rats of the Wistar strain.

They were about 100 days old and experimentallynaive. Prior to the experiment the animals werehoused, 10 to a cage, in large living cages measuring30 by 18 by 12 in.

Apparatus and ProcedureThe rats were divided at random into two groups of

nine each, a control group (C) and an experimentalgroup (E). Over the eight-day experimental periodeach animal was housed in a small living cage, measur-ing 10 by 6 by 5 in., containing a food receptacle 3 by3 by 3 in. All cages contained food and water at alltimes. For at least 22 hr. per day each rat in group Chad free access to an activity wheel of a standard typemeasuring 14 in. in diameter by 4 in. wide. The animalsin group E never had access to activity wheels.

Exploratory behavior was measured in an enclosed,symmetrical, single-unit Y maze constructed fromunpaintcd white pine. Each arm was 24 in. long, 4 in.wide, and 4 in. high (inside dimensions), had a hingedhardware-cloth top, and was marked off into 12-in.sections. The maze was uniformly illuminated by dirnindirect lighting.

Just before being placed in its small living cage forthe first time, each rat was permitted to explore themaze freely for 5 rain, (day 0). Twenty-four hours later(day 1), 72 hr. later (day 3), and 192 hr. later (day 8)each animal was exposed to the maze for 10 min. Therats were always placed in the maze at the choice

438

ACTIVITY DEPRIVATION AND EXPLORATORY BEHAVIOR 439

point. Neither food nor water was ever present in themaze.

The data consist of (a) the number of activity-wheelrevolutions per day for each animal in group C, (6)the number of 12-in. maze-section traversals for eachanimal during each minute of each maze exposure, and(c) the sequence of maze arms entered by each animalon each maze exposure.

After the maze exposure on day 8, four animals,matched on the basis of amount of exploratory beha-vior in the maze on day 8, were chosen from eachgroup. These rats were kept in the small living cagesfor an additional ten days. Each animal was given freeaccess to an activity wheel for 24 hr. per day. Dailyactivity records were taken. This procedure providesan additional test of the general-activity-drive hypothe-sis. From this hypothesis it follows that the animalsfrom group E, after eight days of activity deprivation,should show an initial high level of activity exceedingthat of the rats from the control group, followed by adecrease to the control-group level.

TABLE 1Summary of the Activity-Wheel Data for Group C

PEBIOD IN HOURS

0-2424-7272-1920-192

MEAN

242.7544.6

1905.22666.9

RESULTS

Activity-Wheel Data

Table 1 presents the average number ofactivity-wheel revolutions for group C duringeach relevant experimental period. It is clearthat these animals were fairly active over theeight-day period. Several ran one-half mileor more on one or more days. A day-by-dayanalysis shows a gradual increase in activityover the experimental period.

Figure 1 summarizes the activity-wheeldata for the eight animals selected from groupsC and E. It is apparent that the eight days ofactivity deprivation imposed on the rats ingroup E did not result in an immediate (oreven delayed) higher level of activity thanthat exhibited by group C, or even a higherlevel than that shown during the first eightdays by the group C animals. The groups aretoo small for tests of significance. However,these data suggest that if activity deprivationexerts any effect, it is that of decreasingamount of behavior.

Amount of Exploratory Behavior

The number of 12-in. maze-section traversalsper minute was tabulated for each animal oneach maze exposure. These data are sum-marized in Figure 2, which shows averageamount of exploratory behavior as a functionof time for each group on each day. There areno apparent differences between groups on

700

o eooP3 500

-400

u-300

53200

100 CROUP C (N=4I • • 6GROUP E (N=4) o~-o

700

600

500

400

300

200

100

0 2 4 6 8 10 12 14 16 18DAYS

FIG. 1. Average amount of activity-wheel behavioras a function of days

3 4 6 8 10 2 4 6 6PERIODS OF ONE MINUTE

FIG. 2. Average amount of exploratory behavioras a function of time

any day. The average total number of 12-in.maze-section traversals for groups C andE on days 0, 1, 3, and 8, respectively, are:36.6, 44.1, 41.9, and 45.9; and 33.4, 42.7, 37.1,and 45.8. The respective means for all fourdays are 168.4 and 159.0. None of the differ-ences between these means approaches sig-nificance. It is evident that increasing lengthsof activity deprivation of the kind employed

440 K. C. MONTGOMERY

in this experiment have no effect upon eitherthe amount of exploratory behavior in a simplemaze or its relation to time of exploration.

Orderliness of Exploratory Behavior

As in previous studies (e.g., 4, 5), a measureof the orderliness of exploratory behavior wasobtained by (a) tabulating the number oftimes each animal entered three unlike mazearms in succession and the number of timesit could have done so for each maze exposure,(I) summing both sets of values for each group,and (c) converting them into percentages. Theresults are summarized in Table 2. Inspectionof the table reveals no differences betweengroups on any one day or on all days com-

TABLE 2Per Cent Choice of Three Successive Unlike Arms

On Each Day

DAY

0i38

Total

GltOU

N*

758584

102346

P C.

%

74,369.168.871.870.9

GRO0

N

59937093

315

P E

%

67.869.468.072.769.7

* N represents the total number of triads containing three unlikemembers.

bined. The average percentage for both groupsover all four days is 70.3, a value in closeagreement with corresponding percentagesfound in previous studies (5, 6) in which femalerats were used. In brief, activity deprivationof the kind employed in this experiment hasno effect upon the orderliness of exploratorybehavior in a simple maze.

It should also be mentioned that £ detectedno qualitative differences in the maze behaviorof the animals in the two groups.

Correlational Data

Although the number of animals per groupis relatively small, several rank-order cor-relation coefficients were computed. The test-retest rho (first three days vs. last five days)for the activity-wheel measures taken ongroup C is .88. The test-retest rho (days 0and 1 vs. days 3 and 8) for amount of mazebehavior for all 18 rats is .80. Both values are

significant at the .01 level (2, pp. 46-49). Therho for total amount of activity in the drumsover the first three days vs. the total amountof maze behavior on day 3 for group C is .81.The corresponding rho for the last five daysin the drum vs. maze activity on day 8 is .10.The former value is significant at the .01 level;the latter does not differ from zero. In brief,both the activity wheel and the maze arefairly reliable measuring instruments, and theinitially high correlation between drum andmaze activity drops to zero during the latterpart of the experimental period.

DISCUSSION AND CONCLUSIONS

The results of this experiment are unequivo-cal. They show that moderate activity dep-rivation over an eight-day period (a) has noeffect upon the amount of exploratory be-havior of rats in a simple maze, upon its rela-tion to time of exploration, or upon its ordercharacteristics, and (b) does not lead to anabove normal amount of activity-wheel be-havior. These findings are completely negativewith respect to the hypothesis that explora-tory behavior is motivated by the generalactivity drive. On the other hand, they sup-port the author's hypothesis that the explora-tory drive is a relatively independent primarydrive aroused by novel external stimulation.

A possible criticism of the present experi-ment is that the animals in group E may havebeen as active, or nearly so, outside of themaze as those in group C. None of the author'sobservations supports this criticism. Everytime E entered the room in which the animalswere kept, the animals in group E were asleep,lying quietly, or otherwise inactive, whereasthose in group C were generally "up andabout." It was often necessary to take pre-cautions to insure that the rats in group Ewould be awake and active for their maze ex-posures. Moreover, it is difficult to see howthe animals in group E could have been nearlyas active as those in the other group. The livingcages were so small that the rats could barelyturn around comfortably; on the other hand,the group C animals could (and frequentlydid) run back and forth between the activitywheels and their cages without actually turn-ing the wheels.

The initial high correlation between amount

ACTIVITY DEPRIVATION AND EXPLORATORY BEHAVIOR 441

of activity-wheel and maze behavior and itssubsequent decrease to zero merit discussion.Each apparatus proved to be a fairly reliablemeasuring instrument; hence the explanationmust be sought elsewhere. It seems likely thatduring the first two or three days the activitydrums presented relatively novel stimuli tothe animals in group C, as did the maze. Hence,both situations evoked exploratory behavior,and the correlation was high and positive.With repeated exposures the exploratory-drive-evoking power of the activity wheelsdecreased, other factors began to operate, andthe correlation dropped to zero. The natureof these other factors is open to empirical in-vestigation. However, the activity-wheel datasuggest that some kind of learning or adapta-tion occurred: there was a gradual increasein average activity over the eight-day periodfor group C, and Figure 1 reveals a similartrend for both subgroups.

It should be noted that these data corrobo-rate, rather than contradict, Anderson's (1)report of zero correlations between activity-wheel behavior and exploratory behavior. Hekept his animals (male rats) in activity wheelsfor eight weeks, and used only the measurestaken during the last four weeks in computinghis correlations.

Two major conclusions are drawn from theresults of this experiment, (a) Because pro-longed moderate activity deprivation exertsno effect of any kind upon the exploratory be-

havior of rats in a simple maze, it is concludedthat exploratory behavior is independent ofthe general activity drive, (b) For the samereason, and because of previous data (6), itis concluded that the exploratory drive is arelatively independent primary drive arousedby novel external stimulation. The data fromthe present study, especially those summarizedin Figure 1, provide no support for the con-cept of the "general activity drive"—a modernversion of the "excess energy theory." Afurther and a very tentative conclusion is thatthis concept may not be useful in the analysisof behavior.

REFERENCES

1. ANDERSON, E. E. The interrelationship of drives inthe male albino rat: II. Intercorrelations be-tween 47 measures of drives and of learning. Comp.Psychol. Monogr., 1938, 14, No. 6.

2. KENDALL, M. G. Rank correlation methods. London:Charles Griffin, 1948.

3. MONTGOMERY, K. C. The relation between explora-tory behavior and spontaneous alternation in thewhite rat. /. camp, physiol. Psychol,, 1951, 44,582-589.

4. MONTGOMERY, K. C. Exploratory behavior and itsrelation to spontaneous alternation in a series ofmaze exposures. /. comp. physiol. Psychol., 1952,46, 50-57.

5. MONTGOMERY, K. C. Exploratory behavior as afunction of "similarity" of stimulus situations,J. comp. physiol. Psychol., 1953, 46, 129-133.

6. MONTGOMERY, K. C. The effect of the hunger andthirst drives upon exploratory behavior. J.comp. physiol. Psychol., 1953, 46, 315-319.

Received March 9,1953.