Dopamine controls fundamental cognitive operations of multi-target spatial working memory.

This study addresses computationally how the prefrontal cortical circuit performs operations of multiple items in spatial working memory. The basic idea is that dopamine controls the circuit dynamics for the operations by changing the ratio of the NMDA-channel transmission to the AMPA-channel transmission. There is evidence that this ratio is a function of dopamine D1 receptor activation. The simulation shows that the model circuit performs several different operations of multi-target spatial working memory depending on this ratio. When the ratio is low, 'replacement' occurs from the previously loaded target to a new one. In intermediate levels of the ratio, a new target is 'added' to the previously loaded target, resulting in the coexistence of more than one target. For higher ratios, the circuit 'rejects' other succeedingly received target stimuli. This study suggests four important issues: First, the cortical circuit can perform operations of multi-target spatial working memory. Second, the circuit can switch the modes of the operations by changing the NMDA-to-AMPA ratio. Third, dopamine would have major roles in the operations of multi-target spatial working memory. Fourth, the intracortical inhibition (especially of the cross-directional) plays an important role in regulating the competition between targets.