Reliable optical detection of coherent neuronal activity in fast oscillating networks in vitro

► We observe spontaneous calcium transients in cultured hippocampal slices. ► Protein-based calcium dyes are expressed by viral gene transfer. ► Signal-to-noise ratio is optimized by wavelet-based filtering. ► Single cells can be distinguished by a rigid classifying algorithm. ► Our method allows analysis of co-active assemblies of multiple neurons.