The ability to extract DNA from human brain tissue has provided a unique technical strategy in looking for gene sequence alterations associated with human neurological and psychiatric diseases. In particular, somatic gene mutations may be detected in brain lesions, such as brain tumors or malformations, but not in peripheral blood, providing key molecular insights into the pathogenesis of these disorders. Recent studies have shown that genomic DNA can be reliably extracted from single microdissected cells in the brain so that gene sequence alterations can be co-analyzed in association with particular morphological, neurochemical, or spatiotemporal features of select cell types.