The model has eight parameters: a, b, c, d, r, s, x R and I. It is common to fix some of them and let the others be control parameters. Usually the parameter I, which means the current that enters the neuron, is taken as a control parameter. Other control parameters used often in the literature are a, b, c, d, or r, the first four modeling the working of the fast ion channels and the last one the slow ion channels, respectively. Frequently, the parameters held fixed are s = 4 and x R = -8/5. When a, b, c, d are fixed the values given are a = 1, b = 3, c = 1, and d = 5. The parameter r governs the time scale of the neural adaptation and is something of the order of 10, and I ranges between −10 and 10.