Effects of phentermine and pentobarbital on choice processes during multiple probability learning (MPL) and decision processes manipulated by pay-off conditions
✍ Scribed by E. R. Volkerts; M. W. Van Laar; M. N. Verbaten; G. Mulder; R. A. A. Maes
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 235 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0885-6222
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✦ Synopsis
The primary research question in this investigation concerned whether arousal manipulation by a stimulant (phentermine 20 mg) and a depressant (pentobarbital 100 mg) will oppositely aect choice behaviour in a probability learning task and decision processes manipulated by pay-o. A 3-source probability learning task was used for this purpose, in that, upon the presentation of a pacing cue (every 2 s) which initiates a sampling response required the subject to predict which source will contain a signal. Three groups of 12 subjects received the drugs or placebo, double-blind and crossover. One group performed the task under an all-or-none pay-o function (V1), wherein correct responses on the high (0 . 60), medium (0 . 30) or low (0 . 10) probability source were equally paid; the second group performed the task under a pay-o function, approximately inversely proportional to the signal probability ratio (V2), wherein their gain was maximal on the low probability source when their predictions were correct on this event; while the third group was paid according to a pay-o function (V3), closely related to the ®rst, in that, the maximum gain could be reached when predictions were correct on the high or medium probability source. The results showed that pentobarbital signi®cantly increased sampling responses on the low probability source in the V1 group, while the eects of phentermine did not reach signi®cance when compared to placebo. In the V2 group, no signi®cant treatment eects were found on sampling responses on the high, medium or low probability source a ®nding explained in the context of arousal theory. Further, in the V3 group relative to placebo, both phentermine and pentobarbital marginally signi®cantly increased and decreased sampling responses on the medium probability source, respectively. These eects reached signi®cance on the low probability source for both drugs when compared to placebo. It was concluded that: (1) the results generally con®rm the expectations regarding the dierent pay-o conditions and the general ®nding that full maximization is hardly ever found in probability learning experiments;
(2) the expected eects of the drugs were overall small but consistent and in the hypothesized direction; (3) signi®cant drug eects were mostly found on the low probability source; (4) pentobarbital produced more behavioural changes than phentermine.