LOW SPIKING RATES IN A POPULATION OF MUTUALLY EXCITING PYRAMIDAL CELLS

In a recurrent artificial neural network, the units active in an attra ctor state typically reach their maximum activity value while the othe rs are quiescent. In contrast, recordings of cortical cell activity in vivo rarely reveal cells firing at their maximum rate. This discrepan cy has been one of the main arguments against using attractor networks as models or cortical associative memory. In this study we show that low-rate sustained after-activity can be obtained in a simulated netwo rk of mutually exciting pyramidal cells. This is achieved by assuming that the synapses in the network are of a saturating type. When the ap plication of a monoamine neuromodulator is simulated, after-activity w ith firing rates around 60 s-1 can be produced. The firing pattern of the network was found to be similar to that of the experimentally most comparable system, the disinhibited hippocampal slice. The results ob tained are robust against simulated biological variation and backgroun d noise.