Dennis D. M. O'Leary

Leader in the study of neural development who made fundamental discoveries in three broad areas. (1) He discovered that neural connections in the vertebrate CNS arise from branches that form de novo from the primary axon shaft days after it passed its targets forming initially exuberant axonal projections followed by large-scale, selective axon pruning independent of neuronal death. (2) He identified cellular and molecular mechanisms for the development of topographic maps, in particular, the role of bidirectional ephrin/Eph signaling. (3) He defined diverse mechanisms that control patterning of the cerebral cortex, including the roles of multiple transcription factors expressed in complementary gradients whose levels specify area identity in cortical progenitors and their neuronal progeny and the role of thalamic input in differentiating primary from higher order sensory areas.