Physiology and Behavior. Vol. 3, pp. 571-573. Pergamon Press, 1968. Printed in Great Britain
Schedule-Induced Wheel Running' DAVID LEVITSKY AND GEORGE COLLIER
Rutgers--The State University, New Brunswick, New Jersey (Received 27 J a n u a r y 1968) LEVITSKY, D. AND COLLIER, G. Schedule-inducedwheel running. PHYSIOL.BEHAV.3 (4) 571-573, 1968.--Rats reinforced for bar pressing on a variable interval schedule were allowed access to a running wheel. Wheel running displayed many of the characteristics of schedule-induced drinking. These data call into question the explanations of schedule-induced drinking based entirely upon thirst motivation, and suggest that it is only one of a number of post-reinforcement behaviors affected on an intermittent reinforcement schedule.
FALK  REPORTED that rats reinforced with food pellets for bar pressing on a variable interval (VI) schedule consume abnormally large quantities of water. The drinking occurs almost immediately following the delivery of the pellet. This behavior was shown to be entirely under the control of the reinforcement schedule. At high densities of reinforcement the amount of water consumed is small. As the density of reinforcement decreases on either interval or ratio schedules, the amount of water consumed increases and then decreases at the very low densities [5, 6]. Skinner and Morse  reported that rats reinforced for bar pressing on a long fixed-interval schedule and allowed access to running wheels display high levels of running during the interreinforcement interval. The present study attempts to demonstrate that this kind of wheel running has many of the same characteristics as the schedule-induced drinking and may be a reflection of the same behavioral process.
The animals were maintained throughout the experiment at 80 % of their body weight by means of food restriction and were tested daily. F o o d consumed during the test session was subtracted from the daily ration. The animals were first trained to press the bar on a continuous reinforcement schedule (CRF). They were given 15 sessions of bar pressing reinforced on a (VI) schedule with a geometric mean of 1 min and a minimum interreinforcement interval of 15 sec and a maximum of 4 min. During this time the animals had access to water but not to the running wheel. The sequence of experimental conditions is presented in Table 1. All sessions were 1 hr long. RESULTS
The mean wheel turns, total bar presses and total number of licks per session are presented in Fig. 1. The direction of the changes in response rates between conditions was the same for all 5 animals. During the initial stage of the experiment the subjects displayed the classical schedule-induced drinking. Average intake of water on last 4 days of drinking was 33 ml. When the drinking tube was replaced b y the running wheel, running behavior displayed an acquisition curve very similar to that of the drinking behavior, so that after 15 days the rat was running at 325 turns per hour. Bar pressing, as would be expected, decreased during C R F and increased rapidly following the return to the VI schedule. Running declined as soon as the reinforcement schedule was changed to C R F and increased just as rapidly when the VI schedule was reinstated. During extinction both bar pressing and wheel running displayed typical extinction curves. Upon the return to the reinforcement schedule both measures again increased; running increased to its previous level and bar pressing increased to a slightly greater level. When access to the running wheel was not permitted, bar pressing rate showed an immediate increase which returned to previous levels as soon as the running was again allowed. Running during this period showed a large increase on the first and
Subjects The subjects were five male, albino rats of the SpragueDawley strain, approximately 144 days of age at the start of the experiment,
Apparatus The apparatus consisted o f a Wahmann (LC-34) (14 in. dia.) running wheel and a Davis pellet dispenser capable of delivering 45 mg Noyes pellets. A bar and pellet bowl were attached to one side of the running wheel home cage. A standard 100 ml Wahmann (LC-274) drinking tube with a glass spout (5 mm dia.) was located on the opposite side of the home cage from the bar and pellet dispenser. Licking was measured via a Grason-Stadler electronic Drinkometer (F_A690A) attached to the drinking tube. A running response was electrically recorded when the animal made one complete revolution of the wheel. Running, licking, and bar pressing were recorded on an Esterline Angus event recorder located, with all programming equipment, in an adjacent room.
tThis work was supported by Grant HD-00941 from the National Institute of Mental Health, Bethesda, Maryland. 571
LEVITSKY AND COLLIER TABLE 1 EXPERIMENTAL
1- 15 16--30 31-36 37--42 43-52 53-62 63-72 73-83 84-94 96-109 110-119
Sessions Reinforceper ment Condition Schedule 15 15 6 7 10 10 10 11 12 14 10
VI VI CRF VI Extinction VI VI VI VI V1 VI
yes no no no no no no no yes yes no
no yes yes yes yes yes no yes yes no yes
I~p * BP +
The wheel running behavior exhibited in this study bears a striking resemblance to schedule-induced drinking. There are at least three homologies suggesting that both behaviors are controlled by the same mechanism. First, neither induced wheel running nor induced drinking behavior (4) occurs under CRF. The introduction of CRF in the present study leads to an immediate reduction in wheel running. This reduction occurs before the subject has consumed a substantial amount of food. Secondly, both behaviors are dependent upon the occurrence of the reinforcement. This has been clearly shown previously by Falk  for polydipsia. In the present study, the extinction of the bar pressing response has an immediately depressing effect upon running which then shows rapid recovery upon return to the VI schedule. Thirdly, both running and drinking occur immediately following the reinforcement.
BP BP IlD~I
800C cn 60O(: O _1
300 ;, ,.,
l ",/ ;
FIG. 1. Average number of licks, wheel turns, and bar presses (BP) per session per day. Letters at top of each block describe responses available; (L) licking the water tube, (R) running, (BP) bar pressing.
second day, declining to prior levels on the third day. The addition of the drinking tube in the next stage of the experiment had little, if any, effect upon either bar pressing or wheel running behavior. The average amount of water drunk during this period was 22 ml. When the running was again eliminated bar pressing increased to about the same level as had occurred previously in the experiment. Bar pressing rate was depressed when running was again allowed. Figure 2 shows a typical individual record of one subject under three conditions: Free access to (1) the wheel, and (2) the drinking tube, (3) both the wheel and drinking tube. When either running or drinking was allowed, the initial response occurred very shortly after the occurrence of the reinforcement. Whereas drinking almost always appeared only as a single burst of licking, running occurred throughout the interreinforcement interval. When the animal was given the opportunity to run and/or drink, drinking always occurred following the reinforcement and wheel running was distributed throughout the interreinforcement interval, a phenomenon similar to that observed under conditions of running only.
o~ FIN, ~N
~ R~ ~°" LICK
W W m ....
1 | ~
FIG. 2. Response patterns in each of three experimental situations: Top (BP & Licking); Middle (BP & Running); Bottom (BP & Licking & Running).
SCHEDULE-INDUCED WHEEL RUNNING
There are, however, two distinct differences in the pattern of responses for these two behaviors. Drinking occurs almost always as a brief burst immediately following the reinforcement, whereas running, which also occurs immediately following the reinforcement, continues to occur throughout the interreinforcement interval. This difference in the distribution of the two behaviors probably accounts for the suppression of bar pressing when the animal was permitted to run, and the absence of such an effect with drinking. The other difference between the two behaviors can be seen when both are allowed at the same time. Drinking almost always occurs prior to running. There are two current explanations of schedule-induced drinking. One hypothesis suggests a thirst-based mechanism caused by dry mouth  or post-prandial thirst . If both schedule-induced drinking and running are indeed controlled by the same mechanism, as suggested above, then this interpretation cannot be correct. The other hypothesis suggests that schedule-induced drinking is adventitiously reinforced [I ]. Falk  has shown such explanations of polydipsia to be improbable. Several aspects of the present study strongly suggest that this hypothesis cannot explain schedule-induced running behavior either. Upon the return to the V1 schedule following CRF, the running returned to the previous level immediately. Unless one assumes the behavior to be conditioned to the specific schedule of reinforcement, it is unlikely that a superstitious behavior would reappear so rapidly. Moreover, the behavior
was maintained at approximately the same level throughout the 120 days of the experiment. Adventitiously reinforced behaviors typically disappear over time . Skinner and Morse  interpreted wheel running during the interreinforcement interval as an example of competition between running and bar pressing. A competition explanation would predict an increase in running concomitant with the decreasein barpressing. When bar pressing was extinguished in thepresent experiment running decreased rather than increased. An alternative explanation of these schedule-induced behaviors is that the effect of the reinforcement during intermittent schedules may be to not only strengthen the "preceding" response upon which the reinforcement is contingent, but may also be to momentarily increase the probability of all potential responses in the specific testing situation which may "follow" the reinforcement. Thus, the frequency of such responses--grooming, sniffing, rearing, etc.--would be expected to increase following reinforcement on an intermittent schedule. It seems likely that the schedule is necessary only in that sufficient time is allowed for responses other than eating to occur. The present data raise the possibility that scheduleinduced drinking is only one of a number of post-reinforcement behaviors affected by the reinforcement on an intermittent schedule. Thus, it may be that reinforcement not only affects the probability of the preceding response but may also momentarily increase the probability of other potential responses following the reinforcement in time.
1. Clark, F. C. Some observations on the adventitious reinforcement of drinking under food reinforcement. J. exp. Analysis Behav. 5: 61-63, 1962. 2. Falk, J. L. Production of polydipsia in normal rats by an intermittent food schedule. Science 133: 195-196, 1961. 3. Falk, J. L. The behavioral regulation of water-electrolyte balance. In: Nebraska ~ymposium on motivation, edited by M. R. Jones. Lincoln: University of Nebraska Press, 1961, pp. 1-33. 4. Falk, J. L. Studies on schedule-induced polydipsia. In: Thirst, edited by M. J. Wayner. Oxford: Pergamon Press, 1964, pp. 95-113.
5. Falk, J. L. Schedule-induced polydipsia as a function of fixed interval length. J. exp. Analysis Behav. 9: 37-39, 1966. 6. Falk, J. L. Conditions producing psychogenic polydipsia in animals. Annls. IV. Y. Acad. Sci., in Press. 7. Skinner, B. F. 'Supersition' in the pigeon. J. exp. Psychol. 38: 168-172, 1948. 8. Skinner, B. F. and W. H. Morse. Concurrent activity under fixed-interval reinforcement. J. comp. physiol. Psychol. 50: 279-281, 1957. 9. Stein, L. Excess drinking in the rat: Supersition or thirst? J. comp. physiol. Psychol. 58: 237-242, 1964. 10. Stricker, E. M. and E. R. Adair. Body fluid Balance, taste, and post-prandial factors in schedule-induced polydipsia. J. comp. physiol. Psychol. 63: 449-454, 1966.