PROJECT SUMMARY Salient signals, like aversive stimulation and reward, should be faithfully detected, and processed by the nervous system to generate an adaptive action. One of the universal circuit mechanisms linked to salient signal processing in cortical operation is the activation of dis-inhibitory neurons by subcortical afferents. Aversive signals and reward delivery profoundly excite cortical GABAergic interneurons expressing vasoactive intestinal polypeptide (VIP), which selectively inhibit other GABAergic interneurons, leading to the dis-inhibition of cortical pyramidal cells. In this project, we propose to reveal the functional diversity of VIP interneurons in a cortical structure. The central idea of our project rests on our earlier anatomical findings that distinct groups of VIP interneurons innervate different types of GABAergic interneurons, observations that prompted us to suggest a heterogeneity in their activity during various cortical processes. However, recent imaging studies reported rather similar activity of VIP interneurons following aversive and appetitive stimuli. In contrast to these in vivo imaging data, our preliminary experiments obtained in a frontal cortical area of anesthetized mice have revealed a considerable heterogeneity in VIP interneuron spiking upon delivery of foot shocks. Building on these preliminary results, our goal is to determine the functional complexity of cortical VIP interneurons, including their connectivity and operation in awake mice. To achieve these aims, we will combine viral techniques, neuroanatomical methods, in vivo and in vitro electrophysiology with optogenetics in three different genetically modified mouse lines. The results of this project will uncover the heterogeneity of spike responses generated by genetically defined dis-inhibitory VIP interneurons upon salient signal delivery and their downstream effects on postsynaptic partners within the local microcircuits. Our project will reveal the complexity of dis-inhibitory circuit motifs in cortical networks, which may be a general phenomenon in a cortex- wide manner. In addition, our results will help form novel concepts underlying the pathological operation of cortical circuits linked to deficits in attention and salient signal detection that typifies many malfunctional cognitive processes, including those observed in schizophrenia, autism, and attention deficit.