Probing the function of neuronal populations: Combining micromirror-based optogenetic photostimulation with voltage-sensitive dye imaging

Recent advances in our understanding of brain function have come from using light to either control or image neuronal activity. Here we describe an approach that combines both techniques: a micromirror array is used to photostimulate populations of presynaptic neurons expressing channelrhodopsin-2, while a red-shifted voltage-sensitive dye allows optical detection of resulting postsynaptic activity. Such technology allowed us to control the activity of cerebellar interneurons while simultaneously recording inhibitory responses in multiple Purkinje neurons, their postsynaptic targets. This approach should substantially accelerate our understanding of information processing by populations of neurons within brain circuits.

► An all-optical system for mapping circuits between neuron populations was developed.
► Inhibitory synaptic circuits in cerebellar cortex were detected and mapped.
► Circuits between molecular layer interneurons and Purkinje cells diverge broadly.