Logo IMG


The Experimental Analysis of Behavior

The 1957 American Scientist article, reproduced in full

B. F. Skinner

The Effects of Drugs on Behavior

Other powerful variables which affect operant behavior are found in the field of pharmacology. Some drugs which affect behavior—alcohol, caffeine, nicotine, and so on—were discovered by accident and have had a long history. Others have been produced explicitly to yield such effects. The field is an active one (partly because of the importance of pharmacotherapy in mental illness) and available compounds are multiplying rapidly. Most of the behavioral drugs now available have effects which would be classified in the fields of motivation and emotion. There is no reason, however, why the effects of various contingencies of reinforcement could not be simulated by direct chemical action—why “intelligence” could not be facilitated or confusion or mental fatigue reduced. In any case, the behavior generated by various contingencies of reinforcement (including the control of that behavior via stimuli) are the base lines against which motivational and emotional effects are felt. The present technique for the study of operant behavior offers a quantitative, continuous record of the behavior of an individual organ ism, which is already being widely used—in industry as well as the research laboratory—in screening psychopharmacological compounds and investigating the nature of pharmacological effects.

2012-01SkinnerF14.jpgClick to Enlarge ImageAn example is some research by Peter B. Dews [13], of the Department of Pharmacology of the Harvard Medical School. Dews has studied the effect of certain sedatives on the pigeon’s performance under a multiple fixed-interval fixed-ratio schedule. A standard base line obtained in a short daily experimental session is shown in the upper half of Figure 14. The pigeon is reinforced on a fixed-interval schedule when the key is red and on a fixed-ratio schedule when the key is green, the two schedules being presented in the order: one interval, one ratio, two intervals, ten ratios, two intervals, four ratios. In addition to the usual characteristics of the multiple performance, this brief program shows local effects which add to its usefulness as a base line. For example, the period of slow responding after reinforcement is greater when the preceding reinforcement has been on a ratio schedule—that is, the scallops at a and b are shallower than those at c and d. The effect of moderate doses of barbiturates, bromides, and other sedatives under a multiple fixed-interval fixed-ratio schedule is to destroy the interval performance while leaving the ratio performance essentially untouched. The lower half of Figure 14 was recorded on the day following the upper half. Three milligrams of chlorpromazine had been injected 2.5 hours prior to the experiment. The tranquilizing effect of chlorpromazine develops only with repeated doses; what is shown here is the immediate effect of a dose of this magnitude, which is similar to that of a sedative.. It will be seen that the ratios survive (at e, /, and g) but that the interval performances are greatly disturbed. There is responding where none is expected, as at A, but not enough where a rapid rate usually obtains. This fact provides a useful screening test, but it also throws important light on the actual nature of sedation. The difference between intervals and ratios may explain some instances in which sedatives appear to have inconsistent effects on human subjects.

2012-01SkinnerF15.jpgClick to Enlarge ImageThe interval performance is also damaged by chlorpromazine in a different type of compound schedule. Ferster and the writer have studied the effect of concurrent schedules in which two or more control ling circuits set up reinforcements independently. In one experiment a rat was reinforced with food at fixed intervals of 10 minutes and also by the avoidance of shock, where a shock occurred every 20 seconds unless postponed for 20 seconds by a response to a lever. The normal result of this concurrent schedule is shown in the upper part of Figure 15. When the rat is “working for food and to avoid a shock,” its performance suggests the usual interval scallop tilted upward so that instead of pausing after reinforcement, the rat responds at a rate sufficient to avoid most shocks. A one-milligram dose of chlorpromazine immediately before the experiment has the effect shown in the lower part of the figure. The interval performance is eliminated, leaving the slow steady responding characteristic of avoidance conditioning.

2012-01SkinnerF16.jpgClick to Enlarge ImageDrugs which alter emotional conditions may be studied by examining the effect of the emotional variable upon operant behavior. An example is the condition usually called “anxiety.” Many years ago Estes and the writer [14] showed that the normal performance under fixed-interval reinforcement was suppressed by a stimulus which characteristically preceded a shock. In our experiment, a rat was reinforced on a fixed interval schedule until a stable base line developed. A stimulus was then introduced for 3 minutes and followed by a shock to the feet of the rat. In later presentations the stimulus began to depress the rate of responding—an effect comparable to the way in which “anxiety” interferes with the daily behavior of a man. Hunt and Brady [is] have shown that some of the “treatments” for human anxiety (for example, electroconvulsive shock) temporarily eliminate the conditioned suppression in such experiments. Brady has recently applied this technique to the study of tranquilizing drugs. In his experiment, a rat is reinforced on a variable interval schedule until responding stabilizes at a constant intermediate rate. Stimuli are then presented every 10 minutes. Each stimulus lasts for 3 minutes and is followed by a shock. Conditioned suppression soon appears. In Figure 16 each simple arrow shows the onset of the stimulus. In order to isolate the performance in the presence of the stimulus, the record is displaced downward. In the saline control, shortly after the onset of the stimulus, the rate falls to zero, as shown by the horizontal portions of the displaced segments. As soon as the shock is received (at the broken arrows, where the pen returns to its normal position), responding begins almost immediately at the normal rate. The base line between stimuli is not smooth because a certain amount of chronic anxiety develops under these circumstances. A suitable dose of a stimulant such as amphetamine has the effect of increasing the over-all rate, as seen in the middle part of Figure 16. The sup pressing stimulus is, if anything, more effective. A course of treatment with reserpine, another tranquilizer, has the effect of slightly depressing the over-all rate but restoring responding during the formerly suppressing stimulus. Thus, in the lower part of Figure 16, the slopes of the displaced segments of the record are of the same order as the over-all record itself. The reserpine has eliminated an effect which, from a similarity of inciting causes, we may perhaps call anxiety.

comments powered by Disqus


Of Possible Interest

Letters to the Editors: Royal Society Misquoted

Feature Article: Quietest Places in the World

Engineering: Aspirants, Apprentices, and Student Engineers

Subscribe to American Scientist