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The Effects of Meprobamate on the Performance of a Five-Choice Serial Reaction Time Task

Institute of Psychiatry (Maudsley Hospital), University of London

ABSTRACT

The experiment described here arose out of two earlier tests of Eysenck's drug postulate that central depressant drugs increase cortical inhibition. While both studies report similar effects of depressant drugs on pursuit rotor performance and reminiscence, it was unclear from the data whether the impaired performance found was due to an increase in inhibition or to a decrease in excitation, or to both. In order to throw some light on this issue, the effect of meprobamate on a more suitable serial reaction time task was investigated. As expected from Eysenck's postulate, the effects of meprobamate were revealed mainly towards the end of the work period, fall-off in performance during the second half of the test being significantly greater in the drug than in the placebo group. This was thought to be due to the combined cumulative effects of reactive and conditioned inhibition. Measures of these variables in terms of reminiscence and errors respectively showed that differences between drug and placebo were in the predicted direction, but in neither case significant. No difference was found in starting level in the drug and placebo groups, but a comparison with a third group who had previously performed on the task with no treatment indicated a marked "placebo reaction" in those receiving dummy tablets. There was sufficient evidence from the data for the three groups to conclude that an effect of central depressants is probably to decrease excitation as well as increase inhibition. It was suggested, however, that the appropriate excitatory variable involved was drive rather than habit strength, as previously emphasized. The hypothesis was proposed that the habit variables, _SH_R and _SI_R were secondarily affected following a primary effect on the drive variables, D and I_R.