Schematics of a cortical neural circuit model of perceptual decision with different configurations of balanced synaptic input (BSI).

<p>The basic model circuit consists of two strongly-recurrent populations of excitatory neurons (Exc_L and Exc_R) serving as the decision neurons and a population of inhibitory interneurons (Inh) which produces mutual inhibition between the two excitatory populations. There is an excitatory background neural population (ExcBg) that is not selective to task-relevant stimuli and maintains a baseline activity. The two decision populations receive sensory inputs and compete against each other by ramping up its activity and suppressing the other. A decision is made when the population firing rate of a decision population crosses a preset threshold first. A. In first configuration, BSI_ff, the balanced excitatory and inhibitory inputs to Exc_L and Exc_R are generated externally by two pairs of excitatory and inhibitory neuronal populations (ctr1-ctr4) in a feedforward manner. B. In the second configuration, BSI_fb, the balance between excitation and inhibition is generated internally through the feedback inhibitory neurons. The circuit receives a long range excitatory projection from a top-down control module (Ctr) to all neurons in the circuit. The balance between the excitation and inhibition is determined internally by the input strength of Ctr -> Exc (pathway 1) and the increased input strength (comparing to the condition without the Ctr input) of Inh -> Exc (pathway 3) which is driven by Ctr neurons through the pathway 2.