Deep brain stimulation (DBS) is a reversible neuromodulation technique used to treat disorders such as Parkinson’s disease and epilepsy. Despite its clinical success, the underlying neural mechanisms remain unclear. Voltage fluorescence microscopy enables artifact-free recording of single-cell and population membrane voltage signals in awake animals, offering a powerful tool to study DBS mechanisms. After introducing voltage imaging and its use in dissecting brain circuits, I will show how DBS modulates and entrains single-cell action potentials and membrane potential dynamics. Applying these optical techniques in disease models may reveal novel insights into the therapeutic mechanisms of DBS.