Association for Behavior Analysis International

Over 70 years ago, behavioral pharmacology evolved as a scientific discipline integrating behavior analysis and pharmacology starting with the collaboration of B.F. Skinner and Peter Dews at Harvard. One of the first unifying principles that emerged from early research was the notion of rate dependency – that a drug’s effects on behavior was a function of the baseline rate of responding. This led to decades of experimental analysis in behavioral pharmacology. In this symposium, Dr. Jonathan Katz provides a brief history of behavioral pharmacology and rate dependency. Then others present data from several lines of research indicating that rate or baseline dependency remains a useful framework within a variety of domains including behavioral momentum, Dr. Jonathan Pinkston, impulsive and risky choice, Drs. Raymond Pitts and Chris Hughes, and contingency management of drug use, Dr. Stephen Higgins. Dr. Warren Bickel will be our discussant.

In the 1960s Peter Dews and associates published papers indicating that drug effects on operant responding under reinforcement schedules varied with response rates occurring under non-drug conditions. This so-called rate-dependency effect had precedents in physiological pharmacology, particularly in cardiovascular effects of drugs. It is also related to the Law of Initial Values (Wilder, 1962) which states that effects of any agent depend largely on initial levels of the studied variable. A 1964 paper by Dews using fixed-interval schedules examined the specificity of the effects of amobarbital on suppressed responding and was especially notable as it detailed how an evaluation of moderating environmental influences on drug effects could be conducted with due consideration of rate dependency. That analysis also occasioned critiques regarding how to properly express rate-dependent effects. One of these focused on absolute response rate, rather than change as the critical outcome after drug administration. The other considered that average response rates under fixed-interval schedules are unrepresentative of bimodal distributions of constituent response rates. Each critique can be shown to be of minimal significance. The empirical ubiquity across species, environmental conditions, and pharmacological agents indicates that rate dependency remains critical in consideration of factors influencing the behavioral effects of drugs.

Rate dependency refers to empirical observations that the effects of an intervention depend on the baseline rate of behavior. Early work on rate dependency occurred in the context of behavioral pharmacology. Repeated demonstrations that drug effects depended on the rates of behavior, and accompanying mathematical descriptions, affirmed the importance behavior itself plays in pharmacological treatments. At the same time, behavior analysis has shown behavior to be determined by environmental factors, raising the question of what factors determine the rate upon which rate-dependency depends. Our group has focused on one factor in particular—reinforcer magnitude. In several experiments, pigeons earned food according to multiple fixed-interval schedules, where the components differed only in the magnitude of the reinforcer earned. In examinations of several classes of drugs, we showed rate-dependent effects across the interval varied inversely with reinforcer magnitude, that is rate-dependent effects were reduced as magnitude increased. Thus, it appears that increasing reinforcer magnitude has a protective effect on fixed-interval behavior. The findings are consistent with the view of behavior proposed by behavioral momentum theory, whereby schedules are seen to establish response rates and reinforcer magnitude (density) establishes resistance to change.

Despite substantial progress over the past two decides characterizing drug effects on impulsive and risky behavior and elucidating some of the relevant neurobiological mechanisms, considerable discrepancies remain in the literature, both within and across studies. In our hands, drugs invariably decrease sensitivity to the particular reinforcement dimensions controlling choice, but the degree to which this effect occurs varies both within and across subjects. As such, using these data to predict drug effects on impulsive and risky choice is tricky. In this talk, selected data from our lab investigating drug effects on sensitivity to reinforcement under continuous choice procedures will be presented. These data strongly suggest that effects of a variety of drugs are best described as baseline dependent. These analyses suggest that baseline/rate dependence, an example of the original Law of Initial Values (see Wilder, 1931,1962), remains a viable concept, one that behavioral pharmacologists and behavioral neuroscientists ignore at their peril.

I will discuss how baseline rate of cigarette smoking or cocaine use are strong predictors of response to abstinence-contingent Contingency Management (CM) interventions. Similarly, duration of abstinence achieved during the treatment period is a strong predictor of the likelihood of sustaining longer-term abstinence. Regarding the latter, I’ll share experimental results from a randomized controlled clinical trial testing the validity of these observations in which 100 cocaine-dependent outpatients were randomly assigned to one of two abstinence-contingent CM treatment conditions (Higgins et al., 2007). In one condition, vouchers were set at twice the usual monetary value (maximum of $1,995 during the 12-week intervention) whereas in the other treatment condition they were set at half the usual value (maximum of $499 during the 12-week intervention). All else in the treatment conditions remained the same across treatment conditions. As illustrated in the figure shown below, increasing the value of the vouchers increased the mean duration of continuous cocaine abstinence achieved during the 24-week treatment period twofold, and as hypothesized, point-prevalence cocaine abstinence was consistently greater among those treated in the high-magnitude voucher condition compared to the low-magnitude condition in assessments conducted every 3 months throughout an 18-month follow-up period. This presentation will put particular emphasis the importance of a positive initial treatment response to achieving longer-term abstinence from drug use. remains critical in consideration of factors influencing the behavioral effects of drugs.