1. An analog neuron comprising: a weighting unit, said weighting unit having a weighting factor, said weighting factor being substantially determined by the resistance of said weighting unit; and an accumulation unit, said accumulation unit comprising a first phase change material, said first phase change material having a plurality of states, said states including: a reset state; a set state obtainable from said reset state by applying energy in an amount corresponding to the set energy of said reset state, said set energy corresponding to the threshold of said neuron, said set state having lower resistance than said reset state, said set state being transformable to said reset state by applying energy in an amount corresponding to the reset energy of said set state; and one or more accumulation states having substantially the same resistance as said reset state, said accumulation states being obtainable from said reset state by applying energy in an amount less than said threshold; wherein said accumulation unit is connected in series with said weighting unit, said first phase change material is in said reset state or one of said accumulation states, and said weighting factor determines the extent of electrical communication between said weighting unit and said accumulation unit.