Although inhibitory interneurons have been extensively studied, their contributions to circuit dynamics remain poorly understood. While it has been suggested that interneurons, especially those belonging to the same subclass, synchronize their activity and impart this synchrony onto their local network, recent theoretical and experimental works have begun to challenge this view. In addition, there is a variety of subtypes of interneurons, each of which possesses different physiological properties and preferable postsynaptic targets, and they are connected one another, resulting in the diverse inhibitory-inhibitory interactions and possible disinhibitory effects. This suggests that the investigation of the subtype specific function is a key for understanding their contribution to the regulation of the network states. To better understand the function of inhibitory interneurons, we study the subtype specific functional contribution of the interneurons to the network states by optogenetically manipulating each specific subtype, in combination with in vivo multi-cellular two photon Ca imaging, to monitor the network state of the surrounding neurons. Gene expression system based on the adeno-associated virus (AAV) was used with subtype specific Cre transgenic mice so that we could genetically and optogenetically control the activity of interneurons in a region-specific and subtype-specific manner. ArchT, which hyperpolarizes expressing neurons upon an exposure of specific wave-length light, was selected to temporarily inactivate the interneurons in the local neural circuits. AAV encoding GCaMP, a genetically encoded calcium indicator, was also injected to monitor activities of multiple neurons within the neural networks, at single cell resolution, with the two photon microscopy. Information processing in a brain is modulated by a balance between external stimuli (e.g. sensory stimuli) and internal (or spontaneous) patterns. We address those issues by the observation in a mouse primary visual cortex, together with visual stimulation, to compare functions of interneuron subtypes in different states.