Brain Development Neurogenesis Proliferation of neurons through cell

Brain Development • Neurogenesis: Proliferation of neurons through cell division • Neurons migrate to final destination in the nervous system

• Once in place, neurons first grow an axon and then dendrites • Axons elongate as they grow toward specific targets – Myelination begins prenatally and continues at least into adolescence • Dendrites undergo “arborization” – Increase in size and complexity of the dendritic “tree”, including growth of spines on the branches • Increases capacity of dendrites to form connections with other neurons

• Synaptogenesis begins prenatally but mainly occurs postnatally – General pattern involves overproduction of synapses followed by synaptic “pruning” (elimination) – This general pattern occurs at different times in different areas of the brain

• In general, more frequently activated synapses are more likely to be maintained (“use it or lose it”) • Environmental experiences play a role in maintenance and pruning of synapses

Experiential Mechanisms in Brain Development • Experience-expectant synaptogenesis – Occurs as a result of species-typical experiences • Ex: Visual cortex “expects” exposure to light and patterned visual information—needs these sensory inputs to develop normally

• Experience-dependent synaptogenesis – Occurs as a result of idiosyncratic individual experiences across the lifespan • Ex: String musicians have more connections in the area of the cortex representing the fingers of the left hand