Pinkston, J. W. & Branch, M. N. (2004).
Effects of cocaine on performance under fixed-interval schedules with a small tandem ratio requirement.
Journal of the Experimental Analysis of Behavior, 82, 293-310.
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.
Key words: cocaine, tolerance, fixed-interval schedules, tandem fixed-interval
fixed-ratio schedules, log-survivor functions, key peck, pigeons