The effects of methamphetamine and pentobarbital on the running memory span

Summary

The effects of two drugs on the running memory span were tested in 18 young men who served as their own control under double blind conditions. Each of the three treatments-methamphetamine, pentobarbital, and saline placebo-was administered intravenously and repeated in a balanced design. Ss were tested on strings of digits, varying in length from 8 to 20 items, the first eight presented at the rate of one item per second, another eight at the rate of one every four sec. The instruction was to reproduce the last five items in the original order.

Performance at the slower rate confirms the conclusion of an earlier experiment, conducted at the rate of one digit per two sec., i.e., that pentobarbital narrows and methamphetamine exerts no detectable effect on the running digit span. No significant drug effects were found at the fast rate of presentation.

It is proposed that two components determine the running digit span; one involves shifts of attention as the input changes, the other its organization, rehearsal, and other strategies by which the information is stored and made available for recall. Pentobarbital, in the dose used and under the conditions of this study, impairs the latter and does not affect the former.