ABSTRACT
Introduction This chapter reviews the extant twin studies reporting on the heritability of processing speed. In general the heritability of this trait is modest, but its proximity to actual neurobiology (e.g., when operationalized as nerve velocity or electrophysiological recording) makes it a useful endophenotype in the search for genetic variation causing individual differences in general cognitive abilities. Furthermore, indices of impaired processing speed traditionally playa role as biomarkers in disorders like reading disability, autism, and attention-deficit/hyperactivity disorder. For instance, we recently showed in a genome scan for IQ that the genomic regions influencing IQ overlap with areas previously implicated in these disorders. Heritability of processing speed, therefore, can be expected to overlap with heritability for these disorders and, with this chapter, we aim to encourage gene hunters for these afflictions to add measures of processing speed to their gene finding efforts.
