Emergent properties of the prefrontal cortical circuit for working memory processing

In the monkey brain performing a spatial working memory task, tuned activity of the prefrontal cortical neurons that is sustained during the delay period is a neuronal substrate of the working memory. The sustainment of the activity would be attributable to the intrinsic dynamics of the prefrontal cortical circuit because the cue input, which triggers the dynamics, is turned off and no additional external input is provided in the delay period. To understand the intrinsic dynamics of the prefrontal cortical circuit, I show the computer simulations of a model prefrontal cortical circuit with biologically plausible leaky integrate-and-fire neurons. The excitatory (inhibitory) synaptic inputs to the pyramidal cells whose preferred directions are close to the cue direction increased (decreased respectively) gradually while receiving the cue-related input and remained high (low respectively) during the delay period. Opposing effects were observed for the pyramidal cells whose preferred directions are almost anti-parallel to the cue direction. These simulations suggest that the tuned excitatory and inhibitory synaptic inputs are formed in the prefrontal cortical circuit. These synaptic inputs persist even after the termination of the cue-related input, accounting for the tuned delay-period activity for spatial working memory