PI3K/AKT signalling is a major regulator of neuron survival. It blocks cell death by both impinging on the cytoplasmic cell death machinery and by regulating the expression of genes involved in cell death and survival. In addition, it may also use metabolic pathways to regulate cell survival.The PI3K/AKT pathway also affects axon diameter and branching (Marcus et al, 2002) and regulates small G proteins like RhoA (Vanhaesebroeck, B and Waterman, MD, 1999), which control the behaviour of the F-actin cytoskeleton. Moreover, through its connection with the TOR pathway, it promotes translation of a subset of mRNAs.