Four Stimulants of the Central Nervous System: Effects on Short-Term Memory in Young versus Aged Monkeys*

Abstract

Aged Rhesus monkeys and young control monkeys were tested in a delayed-response procedure to assess the effects of CNS stimulants on short-term memory (STM). Previous research established that the aged monkeys showed specific impairments of STM in the procedure. Different CNS stimulants (4: methylphenidate, magnesium pemoline, a pentylenetetrazole/niacin mixture and caffeine) were evaluated on the basis of their relevancy to current geriatric-psychopharmacologic research. Different doses (4) of each of the 4 CNS stimulants were given to each monkey, counter-balanced for possible order effects. Methylphenidate and caffeine impaired the performance of both age groups in the nonhuman primate cognitive task even at relatively low dose levels. Magnesium pemoline produced fewer adverse effects and some evidence of improving STM in the aged monkeys, although not within the levels of statistical significance. The pentylenetetrazole/niacin mixture produced a 3-way interaction involving age, dose and retention interval. Apparently, no definite effects were noted under the 0 s control condition but statistically significant age-related deficits did occur in the STM-dependent retention interval as the dose varied. These 4 CNS stimulants did not improve and may impair performance of tasks requiring STM. Apparently, general CNS stimulation may not constitute significant therapy for cognitive impairments associated with advanced age.