Methamphetamine and pentobarbital effects on human motor performance.

Abstract

Speed in three types of repetitive motor performance, and manual reaction time was tested at different levels of task complexity, on 36 students who served as their own control over repeated sessions, in which they received intravenous doses of methamphetamine, pentobarbital, and placebo adjusted to their body weight. The simpler the task the more likely was methamphetamine to speed up and pentobarbital to slow down performance rate. Compared with placebo, pentobarbital significantly affected rate in counter pressing, and tended to retard performance in a manual skill of finer co-ordination as well as in a cancellation test. Methamphetamine significantly speeded counter pressing with the dominant hand, but exercised that effect on the other hand only over the first minute of performance. Acitvity rate in the manual dexterity test was significantly faster on methamphetamine than on pentobarbital. Individual variability in work rate over successive time samples, and decrement over time, tended to be highest with methamphetamine. The favorable effect of methamphetamine on performance rate may thus stem primarily from an initial spurt that cannot be sustained, although it may revive after intervals longer than those investigated in the present study. No methamphetamine effect could be determined in several tests of reaction time, but pentobarbital slowed down responses, whether warning signals were provided or not. A slow rate in repetitive motor performance with barbiturates may, therefore, be partly attributable to a delay in monitoring cues for response.