Genes and the parsing of cognitive processes.

Now that the human genome has been sequenced there exists the possibility of identifying specific genes that affect human cognition. In this article, recent studies that have found associations between common gene variants and specific cognitive processes are reviewed. Several principles for evaluating this new field are also discussed. The interpretation of results is far from simple because a single gene can affect multiple processes, multiple genes can impact on a single process, and multiple cognitive processes are intercorrelated. In general, functional neuroimaging has been a more sensitive assay of cognitive processing than behavioral measures used alone, although there are important caveats regarding its use. Replicated findings so far involve associations between a COMT polymorphism and prefrontally-based executive functions and neurophysiology, and a BDNF polymorphism and medial-temporal-cortex based declarative memory processes. Implicit in this review is a concern that many of the cognitive paradigms used evolved for purposes well outside those described here. As such it may be necessary to view cognition in novel ways, based on constraints imposed by genomics and neurobiology, in order to increase the effect size of genotypic influences on cognition.