Some effects of methylphenidate on stimulus control of ratio avoidance behavior in the rat.
Methylphenidate dose decides whether you keep clean stimulus control while reducing shocks.
01Research in Context
What this study did
Scientists gave rats methylphenidate before an avoidance task. The rats had to press a lever when a light came on to stop a shock.
They tested two doses: 2 mg/kg and 4 mg/kg. The rats worked on fixed-ratio schedules where more lever presses meant fewer shocks.
What they found
The 4 mg/kg dose hurt stimulus control. Rats pressed during the wrong lights, but still got fewer shocks overall.
The 2 mg/kg dose only helped on FR 4. It cut shocks without messing up the light discrimination.
How this fits with other research
Snapper et al. (1969) showed discrimination training makes sharp stimulus control. Stretch et al. (1966) now shows high-dose methylphenidate can wreck that control even while behavior stays efficient.
Deitz (1986) found chlorpromazine also changes FR responding when stimulus cues change. Both drug studies warn: schedule design plus drug dose decides if stimulus control holds or breaks.
Sailor (1971) proved strong stimulus control shields behavior from deprivation swings. R et al. adds a new shield-buster: too much stimulant.
Why it matters
If you run avoidance or high-rate programs, remember dose size. A small stimulant boost can cut aversives without harming discrimination. Push the dose higher and you may lose stimulus control even if response rates look good. Check discrimination probes whenever medication changes.
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02At a glance
03Original abstract
After exposure to an avoidance schedule which included a warning signal, a rat was placed on a multiple schedule in which the first component was the same as before, i.e., a single response reset the response-shock interval, delaying shock, and the second component differed only in that four bar-presses were required to postpone shock. A fixed ratio requirement of four responses (FR 4) generated behavior resembling a fixed ratio requirement of one response (FR 1) since responding was controlled by the warning signal but more shocks were received. At a dosage of 2 mg/kg, methylphenidate given intraperitoneally decreased shock frequency during FR 4 periods while FR 1 behavior was not affected; at 4 mg/kg, stimulus control of avoidance responding was impaired during both components. Results at 4 mg/kg were partially confirmed by two animals exposed to an FR 4 avoidance schedule which included a warning signal but with different parameters. Response distributions showed that methylphenidate increased response rates in the absence of the warning signal, i.e., stimulus control of ratio-avoidance behavior was impaired although the increased response rates reduced shock frequency. One hour later responses again occurred more frequently during the signal than in its absence but shocks were less frequent than during control (non-drug) periods.
Journal of the experimental analysis of behavior, 1966 · doi:10.1901/jeab.1966.9-389