Different inhibitory effects by dopaminergic modulation and global suppression of activity

In the dopaminergic network system of prefrontal cortex (PFC)-ventral tegmental area (VTA), physiological experiments have been reported that the D/sub 2/ neurons inhibit the spontaneous activity of PFC neurons. However, the functional role of D/sub 2/ suppression is not understood well. Is the effect of modulatory D/sub 2/ inhibition different from that of GABAergic inhibition? The aim of this research is to reveal the difference between modulatory suppression of D/sub 2/ and global inhibition by interneurons. To compare the effects, we construct two alternative models: (1) all GABAergic interneurons of PFC are modulated by a D/sub 2/ system, or (2) a global interneuron depolarizes; all of PFC pyramidal cells. In computer simulations, we exemplify each of the models using a spiking neural network model with sparse and random synaptic connections. The simulation result shows that model-(1) keeps high correlation between spatial patterns of mean firing rates and the network structure despite the suppression of activity, while model-(2) reduces the correlation. This result suggests that modulatory suppression of D/sub 2/ is more than a global suppression and may play a role in memory retrieval function.