Examining neurochemical determinants of inspection time - Development of abiological model

Inspection time (IT), an information-processing correlate of psychometric i ntelligence, has been extensively studied. Previous research has shown that IT is a reliable correlate of psychometric intelligence across different d evelopmental periods, mirroring developmental trends of fluid intelligence. Despite this extensive previous literature, very little is known about the biological basis of IT. In the present review, we discuss recent results f rom our laboratories examining the neurochemical determinants of IT. In thi s review, we outline the significance of several studies in which performan ce on the IT task is measured before and after modulating key human central nervous system (CNS) neurotransmitters and receptor systems (e.g., choline rgic, serotonergic, noradrenergic, and dopaminergic systems). The results o f these studies indicate a primarily cholinergic basis for IT, although oth er aspects of psychometric intelligence may have serotonergic and dopaminer gic determinants in addition to a cholinergic basis. The results are consis tent with data reporting cholinergic depletion and impaired IT performance in dementia of the Alzheimer's type (DAT). Speculatively, we propose that c ompounds that enhance the release of the neurotransmitter acetylcholine (Ac h) will improve IT and the variance that IT shares with IQ test performance . (C) 2001 Elsevier Science Inc. All rights reserved.