Plasticity: The capacity of the brain to adapt to changing inputs and experiences, which varies with age. New circuitry may develop through axon elaboration and synapse formation in response to changing experiences with selective pruning of synapses and axon elimination occurring through use and disuse. Cell adhesion molecules are utilised in synaptic consolidation with consolidation resulting in synapses being impervious or at least very strongly resistant to disruption. Sensitive period: A period during which the effects of experiences are particularly strong during a limited period in development. Neurogenesis - The generation of new neurons from precursor cells which until recently, was believed to be restricted to brain development early in life. Neurogenesis does however occur in the adult brain but is much more limited in the cells ability to integrate than if it occurs earlier in development. Synaptic pruning - The process by which cell conections are eliminated if they are not used. This process underlies Hebbian synapses where by connections not used are eliminated and those more frequently used are strengthened.