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Learning and recall processes were studied in three experiments with 33 subjects, 1 and 3 h after oral administration of codeine phosphate 25 mg, 50 mg and 100 mg. Recall was measured 3 and 24 h after drug administration. Nine subjects received naloxone i.m. with the 50 mg dose of codeine. Learning and memory were assessed by using associative, serial and concept learning tasks. Flicker fusion frequency was measured to assess the general vigilance level of the subjects. Learning performance in the serial learning task was improved 3 h after administration of codeine 100 mg. Recall in the serial learning task was also improved after codeine 25 mg, but only when the material was learnt after 1 hour and was recalled 24 h after drug intake. To demonstrate the enhanced recall both learning and recall had to take place under the same drug condition. The same test showed a tendency to enhanced recall after codeine 50 mg of material learnt 1 hour after drug intake and recalled 24 h later. This effect was counteracted by naloxone. The data are consistent with the hypothesis that codeine may exert its action via opiate receptors and that this system participates in memory functions.

I The double-blind study on twenty healthy students was an attempt at assessing the effects of 2-week's treatment with amitriptyline (25 mg three times a day) and mianserin (10 mg three times a day), each alone or separatively inbibed with alcohol (0.5 g/kg) on the immediate memory and on the acquisition of a paired-association learning-task. 2 Amitriptyline impaired both the short-term memory-span and acquisition, and alcohol potentiated these effects. The action of mianserin did not deviate significantly from that of the placebo, and it also failed to interact with alcohol. 3 It is concluded that the decrement in learning capacity, that occurs after the 2-week's treatment with therapeutic doses of amitriptyline, reflects changes in both the intrinsic and the regulatory mechanisms of learning.

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The effect of a single oral dose of diazepam 10 mg or chlorpromazine 25 mg on memory in man was examined in a double-blind study, each drug being crossed-over against placebo, with 20 subjects for each drug. Kahn's Test for Symbol Arrangement and a paired association-learning task were used for assessment of acquisition, storage and retrieval, and state-dependency effects. A flicker-fusion test, two coordination tests, and a choice reaction task were used to evaluate alertness in the subjects. Diazepam significantly impaired acquisition, but slightly facilitated recall. Reaction time was shortened after acute diazepam treatment and coordination was impaired after two weeks treatment with diazepam. Acute treatment with chlorpromazine did not change memory or psychomotor performance.

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Forty paid healthy male students participated in two subacute experiments of 6 weeks each. In the first trial 20 of them received bromazepam, thioridazine, and placebo double blind cross over for 2 weeks each, and in the second trial the active agents administered to the other 20 participants were chlorpromazine and sulpiride. The tests used were paired associate learning with nonsense syllables and digit memory span. Before testing the subjects took either an alcoholic or a nonalcoholic bitter drink. As in the previous study from this laboratory, alcohol was found to impair learning capacity. Of the drugs used only bromazepam impaired learning significantly, and the combined effect of alcohol and bromazepam on learning capacity was very deleterious. The adrenolytic effect of drugs did not correlate with their effect on learning. Caution is necessary when prescribing bromazepam for active outpatients at least in doses used in this study.

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