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Fig. 11.2. The leaky integrator neuron model. Leaky integrators at each synapse perform decayed summation of incoming spikes, and the outgoing spikes are generated by comparing the weighted sum with the dynamic spiking threshold. Four types of inputs contribute to the activity: afferent, excitatory lateral, inhibitory lateral, and intracolumnar connections (Equation 11.3). The dynamic threshold consists of the base threshold &theta_b, the absolute refractory contribution &theta_a, and the relative refractory contribution &theta_r (Equation 11.5). The base threshold is a fixed baseline value, and the absolute refractory term has a value of &infin for a short time period immediately following an output spike. The relative refractory contribution is increased as output spikes are generated, and it decays to zero if the neuron stays silent.