EEG/tCS Closed Loop Applications

In the field of tCS, the term closed-loop is best understood when contrasted with open-loop interventions. In open-loop tCS, we apply currents to the brain independently of brain state. When the stimulation parameters are somehow altered as a function of brain state measurements, we use the term closed-loop.

For example, EEG can be used to estimate the peak or mean frequency in a given frequency band, and this used to modify the stimulation frequency in tACS. As another example, the phase of a given frequency may be used to correct tACS phase. These two cases will normally come with different timing requirements: power fluctuations are slow compared to phase changes in EEG.