EFFECTS OF DRUGS ON CHARACTERISTICS OF BEHAVIOR MAINTAINED BY COMPLEX SCHEDULES OF INTERMITTENT POSITIVE REINFORCEMENT

Behavioral base lines with several reproducible properties are useful in investigating the effects of drugs on learned behavior. Differential drug effects on interrelated characteristics of behavior make possible detailed analyses of drug action. In addition, behavioral base lines with complex properties offer an advantage in that they are more sensitive to the effects of drugs than are simple base lines. A simple base-line performance is generated by a fixed-ratio schedule in which an animal is reinforced each time a small, constant number of responses is emitted. Following reinforcement, the animal responds a t a high, fairly constant rate until the next reinforcement. I t has been frequently noted that performance under this schedule is refractory to drugs. The insensitivity of behavior maintained by small ratio schedules is reflected both in the need for using relatively large quantities of a drug in order to observe any change in behavior, and in the precipitousness with which the change occurs. Once the dose is made large enough to affect the animal's performance, a gross disturbance in motor coordination also takes place. When used in a base line that contains other schedules of reinforcement, however, a fixed-ratio schedule becomes a valuable tool, that is, where the fixed-ratio performance may be viewed as a characteristic component of a more complex behavior. FIGURE 1 shows the insensitivity of small ratio schedules and the specificity of drug action upon the multiple characteristics of a complex behavior. This curve is a cumulative record of pecking responses for a single pigeon on a day when it received a 4 mg. dosage of sodium pentobarbital. The number of responses is on the ordinate, and time is on the abscissa. This pigeon was maintained a t 80 per cent of normal body weight on a regimen of partial food deprivation. The short diagonal marks indicate the points a t which the response was reinforced with food. The behavioral base line was a multiple schedule containing 2 component schedules of reinforcement. In the presence of 1 stimulus, the pigeon was reinforced on a small fixed-ratio schedule-the 50th response emitted after the onset of the stimulus was reinforced. In the presence of the other stimulus the schedule was a fixed interval-the first response emitted after 10 minutes from the onset of the stimulus was reinforced. The early portion of the record shows a typical performance. When the ratio component was present, the animal responded a t a high constant rate. When the interval component was present there was a positively accelerated curve up to the reinforcement. Later portions of the figure make