Introduction

The fields of functional brain imaging and molecular genetics are at the forefront of biomedical research because these techniques are rapidly identifying new questions to be addressed and increasing the depth to which old questions can be addressed. The purpose of this chapter is to describe the techniques that will facilitate new understanding of neuroimaging results by adding a molecular genetic approach to examining neuroimaging phenotypes. It is hoped that these genetic techniques will enable researchers to identify the genes that play a role in the processes that underlie brain function.

What is meant by a neuroimaging phenotype, or trait? Examples include receptor density measured by ligands in positron emission tomography (PET) or the location and size of a brain region activated in response to a cognitive task measured by cerebral blood flow techniques. A phenotype could also be a psychiatric diagnosis that has some relationship to neuroimaging measurements. Defined broadly, a phenotype, or trait, is any observable characteristic that has a heritable component. In fact, it is the quantitative nature of neuroimaging that may provide an essential element for making significant progress in finding the genes that underlie the biochemical and molecular pathways of brain function. The choice of the definition of the phenotype in a genetic study is of paramount importance for the success of the research enterprise, as is discussed in Chapter 19.