ACTIVITY-DEPENDENT CORTICAL TARGET SELECTION BY THALAMIC AXONS

Connections in the developing nervous system are thought to be formed initially by an activity-independent process of axon pathfinding and t arget selection and subsequently refined by neural activity. Blockade of sodium action potentials by intracranial infusion of tetrodotoxin i n cats during the early period when axons from the Lateral geniculate nucleus (LCN) were in the process of selecting visual cortex as their target altered the pattern and precision of this thalamocortical proje ction. The majority of LCN neurons, rather than projecting to visual c ortex, elaborated a significant projection within the subplate of cort ical areas normally bypassed. Those axons that did project to their co rrect target were topographically disorganized. Thus, neural activity is required for initial targeting decisions made by thalamic axone as they traverse the subplate,