THE METABOLIC BRAIN PATTERN OF YOUNG SUBJECTS GIVEN SCOPOLAMINE

The effect of an intravenous dose of 0.5 mg of scopolamine on the func tional brain activity of normal subjects performing auditory discrimin ation (CPT) was determined in two independent positron emission tomogr aphy studies with [F-18] 2-fluoro-deoxyglucose. In the first prelimina ry study, the most significant effect found was a reduction in the fun ctional activity of the thalamus. In the second ''hypothesis-testing'' study, an equally prominent effect on thalamic functional activity wa s seen. Because the second study was performed on a high-resolution sc anner with improved methodology, we re-examined scopolamine's effects on those brain regions established as determinants of CPT. Of the regi ons affected, the reduction in cingulate and the increase in basal gan glia metabolic rates were the most notable. We concluded that scopolam ine's effects on the functions of thalamic, cingulate and basal gangli a are the likely causes of scopolamine's well-described attention-alte ring properties. Alterations in these same brain structures could be r esponsible for scopolamine's effects on other cognitive functions, e.g ., memory. Alternatively, scopolamine's effects on other brain structu res such as the hippocampus and frontal cortex could underlie scopolam ine's effects on these other cognitive functions. Studies of scopolami ne's regional metabolic effects in subjects performing these other cog nitive tasks at more than a single dose and at more than one post-drug time are needed to discriminate between these two possibilities.