Effects of Cocaine on Performance Under Fixed‐interval Schedules With a Small Tandem Ratio Requirement

Abstract

Daily administration of cocaine often results in the development of tolerance to its effects on responding maintained by fixed-ratio schedules. Such effects have been observed to be greater when the ratio value is small, whereas less or no tolerance has been observed at large ratio values. Similar schedule-parameter-dependent tolerance, however, has not been observed with fixed-interval schedules arranging comparable interreinforcement intervals. This experiment examined the possibility that differences in rate and temporal patterning between the two types of schedule are responsible for the differences in observed patterns of tolerance. Five pigeons were trained to key peck on a three-component multiple (tandem fixed-interval fixed-ratio) schedule. The interval values were 10, 30, and 120 s; the tandem ratio was held constant at five responses. Performance appeared more like that observed under fixed-ratio schedules than fixed-interval schedules. Effects of various doses of cocaine given weekly were then determined for each pigeon. A dose that reduced responding was administered prior to each session for 50 days. A reassessment of effects of the range of doses revealed tolerance. The degree of tolerance was similar across components of the multiple schedule. Next, the saline vehicle was administered prior to each session for 50 days to assess the persistence of tolerance. Tolerance diminished in all subjects. Overall, the results suggested that schedule-parameter-dependent tolerance does not depend on the temporal pattern of responding engendered by fixed-ratio schedules.

Interval timing under a behavioral microscope: Dissociating motivational and timing processes in fixed-interval performance

“…It predicts, for instance, that changes in reinforcement contingencies, as long as they do not significantly change the periodicity of reinforcement, should have a more substantial impact on run rates and IRTs (more specifically, on the length of response bouts) than on latencies and postreinforcement pauses. This prediction is consistent with reported effects of response requirement on FI and FT performance (Morgan, 1970;Pinkston & Branch, 2004;Shull & Brownstein, 1975;Shull, Guilkey, & Witty, 1972). The model also predicts similar selective effects of changes in response effort (e.g., minimum force to press a lever); the scant empirical evidence on this effect is also consistent with qualitative model predictions (Gollub & Lee, 1966).…”

Influences on Cocaine Tolerance Assessed Under a Multiple Conjunctive Schedule of Reinforcement

“…The overall pattern of tolerance observed in the current experiment is comparable to that observed in studies utilizing comparable schedule parameters from our laboratory (Hoffman et al, 1987;Pinkston & Branch, 2004a;Pinkston & Branch, 2004b;Schama & Branch, 1989;Weaver & Branch, 2008;Yoon & Branch 2004) and other laboratories as well (Nickel et al, 1993;van Haaren & Anderson, 1994). Thus, the current experiment adds to the increasing body of work showing tolerance to the disruptive effects of cocaine on responding by pigeons under multiple schedules of reinforcement.…”

“…In the present study, an FR 5 was employed to determine if the presence of a relatively small ratio requirement would interact with the FI to alter the development of tolerance. The current experiment therefore extends the analysis initiated by Pinkston and Branch (2004b) to a procedure that allows the ratio requirement to be completed at any time within the interval.…”

“…The added presence of a small FR requirement to the FI schedule eliminates this feature. For example, Pinkston and Branch (2004b) exposed pigeons to a three-component multiple FI schedule of reinforcement in which the FI values were similar to those used in the current study. Additionally, each FI component had a tandem FR 5 requirement.…”

“…In the Pinkston and Branch (2004b) study, reinforcement was always delivered contingent on completion of the FR requirement. An alternative method of adding an FR requirement to an interval schedule is to use a conjunctive schedule.…”