Conditioned reinforcing effects of capsules associated with high versus low monetary payoff

Prefrontal expectancy and reinforcement-driven antidepressant placebo effects

Placebo responses in depression exemplify how expectancies and appraisals impact mood. Cognitive and neural mechanisms underlying these responses are still poorly understood, partly due to the difficulty of simulating antidepressant effects and manipulating mood experimentally. To address these challenges, we developed an acute antidepressant placebo experiment involving the intravenous administration of a "fast-acting antidepressant" and a trial-by-trial sham fMRI "neurofeedback" manipulation, purporting to reveal mood-relevant neural responses. Twenty volunteers with major depression underwent this experiment while rating their expected and actual mood improvement. Mixed-effects analyses of trial-by-trial ratings revealed that the "drug" infusion cues induced higher expectancies of mood improvement, while both the "drug" infusion cue and the sham neurofeedback induced a reported mood improvement. Neurofeedback of greater magnitude, compared to lower magnitude, recruited the lateral prefrontal cortex (lPFC). Individuals with greater lPFC responses to neurofeedback displayed: (1) greater effect of previous mood improvement on expectancy ratings and (2) greater effect of sham neurofeedback on mood improvement. Behavioral antidepressant placebo effects were additionally moderated by changes in peripheral β-endorphin plasma levels and depressive symptomatology. These data demonstrate the feasibility of trial-by-trial manipulation of antidepressant placebo-associated expectancies and their reinforcement. We provide initial insights into the role of the lPFC in the interplay between placebo-induced expectancies and mood, as well as preliminary evidence for the role of the opioid system in antidepressant placebo effects.

Preference for gamma-hydroxybutyrate (GHB) in current users

Gamma-hydroxybutyrate (GHB) is a drug with significant abuse potential. The present study aimed to assess the relative value of escalating doses of GHB to current GHB users via the Multiple Choice Procedure (MCP), and to validate that the dose rated highest with the MCP would be self-administered at a greater rate than placebo. Participants were 5 current GHB users who were not currently trying to stop using GHB. To examine the value of escalating doses of GHB, the following doses of GHB were used: 0 (placebo), 12.5, 25, 37.5, and 50 mg/kg. Participants typically assigned higher doses of GHB had higher crossover points on the MCP. During choice sessions, participants made repeated choices between administering GHB, placebo or nothing. All participants selected GHB exclusively (5 out of 5 instances) except for one participant who selected GHB on 4 out of 5 instances, thus 96% (i.e., 24/25) of choices were for active GHB. Based on these data, GHB appears likely to function as a dose-dependent reinforcer for humans based on our sample.

Reinforcing effects of diazepam under anxiogenic conditions in individuals with social anxiety

Diazepam (DZ) reinforcement was tested under anxiogenic (public speaking) and neutral (computer task) conditions. Individuals with social anxiety disorder (n = 11) and healthy controls (n = 11) participated in two 5-session phases. Each phase used a standard choice procedure (2 sample, 3 choice sessions) comparing 10-mg DZ and placebo. During the public speaking condition, DZ preference was greater among the participants with social anxiety compared with controls (81.8% vs. 36.4%; p < .05). Participants with social anxiety also gave DZ significantly higher crossover values on the multiple choice procedure under the speech condition compared with the computer condition. Subjective effects indicated that DZ reduced anxiety when levels were elevated during the speech in socially anxious participants. These results suggest that DZ reinforcement may occur under conditions of heightened anxiety by bestowing therapeutic efficacy.

Reinforcing and subjective effects of methylphenidate: dose and time in bed

So that reinforcing and subjective effects of methylphenidate as a function of dose and level of sleepiness could be evaluated, 21 volunteers received methylphenidate (5, 10, or 20 mg) or placebo on 2 sampling days. After 4 and 8 hr time in bed (TIB), they chose their preferred capsule on 5 days. Methylphenidate was chosen more frequently after 4 hr TIB (60%) than it was after 8 hr TIB (33%). The strongest preference (68%) was seen in the 10-mg group. At 10 and 20 mg, stimulant-like subjective effects were reported. The 10-mg group was more adversely affected by the restricted bedtime and showed more pronounced drug effects with methylphenidate. These results indicate that sleepiness modulates the reinforcing and subjective effects of methylphenidate.

Changing drug choice through conditioned reinforcement: comment on Alessi, Roll, Reilly, and Johanson (2002)

The study by S. M. Alessi, J. M. Roll, M. P. Reilly, and C.-E. Johanson (2002) showed that in human volunteers a choice of placebo over diazepam could be reversed by pairing the drug with a higher monetary reward and the placebo with a lower monetary reward for performance on a computer-based task. The results provide a clear laboratory model of how initially neutral or aversive effects of a drug can be altered by association with positive reinforcement to establish the drug as a conditioned reinforcer and to generate drug-seeking behavior. Parallels from the animal and human literatures are discussed, as are potential future studies and applications of this approach for preventing and reducing drug abuse in humans.

Conditioning history and the reinforcing effects of drugs: comment on Alessi, Roll, Reilly, and Johanson (2002)

Drug reinforcement plays a central role in drug abuse. Drugs of abuse are unconditioned reinforcers whose functional effects are mediated through neuropharmacological mechanisms. The role of conditioning has received attention, but the focus has been on associations between environmental cues and unconditioned drug stimuli. Recent studies by C.-E. Johanson, A. Mattox, and C. R. Schuster (1995) and S. M. Alessi, J. M. Roll, M. P. Reilly, and C.-E. Johanson (2002) have demonstrated that drugs can also acquire functional control over human behavior through conditioning processes. Given the potent effects that conditioned reinforcers (e.g., money) can have on human behavior, studies by Johanson et al. and Alessi et al. should engender further examination of conditioning processes and drug reinforcement.

Modulation of the subjective and physiological effects of drugs by contexts and expectations--the search for mechanisms: comment on Alessi, Roll, Reilly, and Johanson (2002)

Contexts and expectations can change the subjective and physiological effects of psychotropic drugs. Learning and conditioning processes clearly contribute to some of these effects. It must be considered, however, that even the acute effects of drugs can be significantly altered by the context in which they are administered. The challenge is to determine the mechanisms operating to bring about these changes.

Associations between drug use and behavioral repertoire in urban youths

Converging with psycho-social research findings, animal and human laboratory studies indicate that behavioral alternatives are important determinants of drug-taking. To investigate associations between how early adolescents spend their time, i.e. their behavioral repertoire and drug use (use of marijuana, crack/cocaine or inhalants), we analyzed data from an epidemiological sample of 1516 urban middle-school students who had completed private interviews in spring 1993. The interview included a 36-item questionnaire to assess how frequently the youth engaged in different activities; history of drug-taking was assessed separately. Multiple logistic regression was used to estimate associations between drug use and each of seven behavioral domains as well as sex, age and racial-ethnic status. Youths spending a great deal of time working for pay and assuming other adult-like roles were more likely to have initiated drug use (estimated odds ratio, OR = 3.49; p = 0.002). Those who spent much time in religious activities were less likely (OR = 0.2, p <0.001). An exploratory search for interactions disclosed other associations that merit attention in future research. These results corroborate evidence on the potential etiological significance of behavioral repertoire in relation to risk of drug use.