An inverse relationship between baseline fixed-interval response rate and the effects of a tandem response requirement

Previous experiments examining the effects of adding a tandem fixed-ratio response requirement on fixed-interval schedule performance have reported inconsistent results. One variable that may account for such inconsistencies is the baseline response rate in the fixed-interval condition. This possibility was investigated in the present study. Rats were given histories with either interresponse times greater than 11 s or fixed-ratio 40 schedules of reinforcement, which engendered either relatively low or high rates of responding, respectively, in the subsequent fixed-interval condition. A tandem ratio response requirement (fixed-ratio 9) was then introduced. The effects of adding this tandem response requirement were inversely related to the baseline fixed-interval response rates; low rates of responding in the fixed-interval condition were markedly increased, whereas high rates of responding were relatively unaffected. This inverse relationship appears to be similar to the rate-dependent relations observed in behavioral pharmacology. These results may provide an explanation for the inconsistent findings reported in previous studies on tandem fixed-interval fixed-ratio schedules and suggest that principles of behavioral pharmacology research may be applicable to the study of the effects of nonpharmacological variables on schedule-controlled behavior.

Time allocation in a concurrent schedule of social interaction and monetary reinforcement: effects of d-amphetamine

Two mutually exclusive options (socializing versus monetary reinforcement) were concurrently available to two normal volunteers during 60-min experimental sessions under controlled laboratory conditions. The amount of money available in the monetary option was adjusted for individual subjects during baseline conditions until subjects divided their time approximately evenly between a social option in which they could converse with another same-sex volunteer or a monetary option in which money was earned for sitting quietly in a private room. In both subjects studied, d-amphetamine (5-25 mg) increased the percent of time allocated to the social option and total seconds of speech. This effect occurred even though increases in the time allocated to the social option necessarily resulted in a forfeiture of monetary reinforcement. The present results provide the first empirical evidence, to our knowledge, that d-amphetamine can increase the relative reinforcing effects of social interaction.

Effects of alcohol on speaking in isolated humans

Drugs of abuse often increase human social interaction, as is suggested in our cultural drug use practices and has been demonstrated in controlled laboratory studies. The environmental and pharmacological mechanisms controlling these effects remain unclear. The present study examined the importance of a social context for obtaining drug-produced increases in human speech by examining the acute effects of alcohol (0, 22, 45, 67 g) on the amount of speech emitted by six normal volunteers who were producing speech monologues in an isolated context. A within-subject repeated-measures experimental design was used. Alcohol produced a significant dose-dependent increase in total speech. Conversely, response rates on a nonverbal behavioral task (circular-lights device) decreased as an orderly function of alcohol dose. These results suggest that a social context is not a necessary condition for alcohol to increase rates of human speech. Moreover, the decreases in response rates observed in the nonverbal task rule out the possibility that alcohol affected total speech via a generalized increase in overall activity levels.

Acute effects of ethanol and diazepam on the acquisition and performance of response sequences in humans

The present study assessed the acute effects of p.o. administered ethanol (0, 22, 45, and 67 g) and diazepam (0, 10, 20 and 40 mg) in normal adult humans responding under a multiple schedule of acquisition and performance of 10-response sequences. In each component of the multiple schedule subjects were required to complete a different sequence of 10 responses in a predetermined order using three keys of a numeric keypad. In the acquisition component a new response sequence had to be acquired each session. In the performance component the response sequence remained the same from session to session. The higher doses of ethanol (67 g) and diazepam (20 and 40 mg) increased overall percent errors above placebo levels; the lower doses of these compounds had no significant effect. The increases in percent errors were selective across the two schedule components. Ethanol increased percent errors significantly only in the acquisition component. Diazepam increased percent errors significantly in the acquisition component at a lower dose (20 mg) than was necessary to increase errors in the performance component (40 mg). Ethanol (67 g) and diazepam (40 mg) decreased overall response rates as an orderly function of dose. In contrast to the percent errors measure, the effects on response rates were not significantly different across the performance and acquisition components. Peak effects on percent errors and response rates varied between 30 and 70 min and 45 and 80 min postdrug for ethanol and diazepam, respectively, and the duration of effects of the higher doses was greater than 3 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Choice of blind methadone dose increases by methadone maintenance patients

In the present study, a choice procedure was used in an outpatient methadone maintenance clinic to examine preferences for different double-blind methadone dose increases in 5 male patients. Subjects chose between 50 mg vs. 50 mg, 60 mg, 75 mg and 100 mg of methadone. In the 50 mg vs. 50 mg condition, each alternative was selected equally often. Percent selection of the higher doses (60, 75 and 100 mg) over the 50 mg dose of methadone increased in a dose-related fashion. Subject self-reports were consistent with methadone's opiate-like properties with dose-related trends being noted in most scales (e.g. opiate effects, drug liking). Overall, the results show that a choice procedure can be used successfully to assess the reinforcing properties of drugs in methadone maintenance patients and that methadone dose increases can function as a reinforcer in this population even under blind dosing conditions.

Contingent methadone delivery: effects on illicit-opiate use

This study examined the effects of contingent vs. non-contingent delivery of a methadone dose supplement on relapse to illicit opiate use in the context of a methadone outpatient detoxification program. Following a 3-week methadone stabilization period on 30 mg, patients (N = 39) were randomly assigned to a contingent, a non-contingent, or a control treatment group. All patients received identical gradual reductions in their assigned methadone dose. During the dose reduction period (weeks 4-11), members of the contingent (N = 13) and non-contingent groups (N = 13) could obtain daily methadone-dose supplements up to 20 mg, but contingent group members could obtain supplements only if their most recent urinalysis results were opiate negative. Control subjects (N = 13) did not have dose increases available. The contingent group presented significantly lower opiate-positive urines during weeks 8-11 (14% positive) of the detox than the non-contingent (38% positive) or control (50% positive) groups. Additionally, the availability of extra methadone improved treatment retention and increased clinic attendance above levels observed in the control group. The potential for further use of methadone's reinforcing properties in the treatment of opiate dependence is discussed.

Acute marijuana effects on social conversation

The present study assessed the acute effects of smoked marijuana on social conversation. Speech quantity was recorded continuously in seven moderate marijuana users during separate 1 h experimental sessions following the paced smoking of 0, 1.01, 1.84, and 2.84% THC marijuana cigarettes. Subjects engaged in conversation with undrugged partners who smoked placebo marijuana cigarettes. The active marijuana produced significant decreases in speech quantity, increases in heart rate, and increases in self-reports of "high" and sedation. Partners showed no effects in speech quantity or self-reports of drug effects that were systematically related to the doses administered to the subject pair members. The effects on speech quantity observed in the present study after acute dosing are similar to the effects on social conversation reported previously during chronic marijuana dosing. Marijuana appears to be an exception to the general rule that drugs of abuse increase verbal interaction.

Pupillary response to methadone challenge in heroin users

The relationship between self-reported illicit heroin use and pupillary response to a low-dose methadone challenge was examined in 28 men beginning methadone therapy for opiate dependence. Pupil diameter was assessed before and 60, 90, and 120 minutes after a 20 mg methadone dose on day 1 of treatment. Self-reports of opiate drug effects were also taken at these times. There was a significant negative correlation (r = -0.53) between pupillary constriction 120 minutes after drug dosing and the average dollar value of subjects' reported heroin use per week. In other words, those who showed the least pupillary constriction generally reported the highest amount of illicit heroin use. Total years since first opiate use was also a significant predictor of pupillary response (r = -0.46). Self-reported amount of heroin use and years since first opiate use together accounted for 60% of the total variance in pupillary response to the challenge (Mult r = 0.77). Pupillary response to a low-dose methadone challenge appears to be a clinically practical and objective method for determining opiate tolerance levels in applicants for methadone therapy.

Modifying the self-injurious behavior of an infant with spina bifida and diminished pain sensitivity

This clinical case study extends the literature on behavioral treatment of self-injury to an intellectually normal infant with spina bifida and diminished sensitivity to pain. After treatment by attention-play periods plus an aversive tasting substance applied to the injured finger, severe biting of the index finger was eliminated and the finger healed. Follow-up inquiries 2 months, 2 and 3 yr later revealed no biting and no substantial tissue damage.