The ability to reliably record from a large ensemble of neurons, map their functional connectivity, and track the activity over chronic time scale is of paramount importance to basic and clinical neuroscience, as a large number of brain functions are realized by coordinated activation of a neuronal population. Implanted electrodes provide one of the primary neurotechniques by allowing for time-resolved acquisition of individual neuron activity in the living brain. However, their recording stability and density pose major limitations on their scientific and clinical applications. We recently demonstrated that ultraflexible, cellular-dimensioned neural electrodes afford seamless integration with brain tissue and reliable recording of individual neurons for several months. Building upon this platform, we further demonstrate the capabilities of reliable detection and isolation of individual units, as well as functional mapping and chronic tracking of the local circuitry in a neuronal cluster over several months in behaving brain.