Neuronal ensembles with distinct morphological, biochemical, and functional identities are organized into complex circuits in the mammalian brain, and malfunction of specific neuronal types in different networks contributes to diverse pathological symptoms.Taking memory as an example, specific memories are held in a subset of neurons, referred to as engram cells.Conditional genome manipulation in the heterogeneous brain would provide a powerful tool for investigating the encoding and storage of specific memories.Recently, Sun et al.[1] developed a clustered regularly interspaced short palindromic repeats (CRISPR)-associated endonuclease Cas9 system for precise genomic perturbations in specific neuronal subpopulations with high temporal and spatial specificity, which can be widely applied in revealing brain functions including memory.