Closed-loop transcranial stimulation and monitoring is disclosed that includes generating a stimulation signal having a set of first oscillation parameters; applying the stimulation signal transcranially to a patient; monitoring the stimulation signal as applied to the patient; receiving a brain activity signal from the patient; generating a feedback signal based on the monitored stimulation signal as applied to the patient; and generating a modified activity signal by subtracting the feedback signal from the brain activity signal; determining one or more second oscillation parameters of the modified activity signal; and adjusting the set of first oscillation parameters of the stimulation signal based on the one or more second oscillation parameters of the modified activity signal. Closed-loop transcranial stimulation and monitoring is also disclosed in which the patient is engaged in a cognitive task.