Evoked resonant neural activity (ERNA)

ERNA is a stereotyped, decaying high-frequency oscillatory response (on the order of 200 to 500 Hz) evoked in the subthalamic region by each DBS pulse. It was noticed as an unusually large and robust stimulation-locked signal, and its amplitude, frequency, and decay vary systematically with the distance from the stimulating contact to the therapeutic target and with the stimulation parameters.

These properties make ERNA attractive as a real-time marker of lead placement and of target engagement, and as a candidate control signal for adaptive DBS. A practical advantage over spontaneous beta is that ERNA is directly evoked by the stimulation, so it is present whenever stimulation is on and can be measured in the inter-pulse interval, which partly sidesteps the problem of sensing a weak spontaneous rhythm through a large ongoing stimulation artifact. Its mechanism and full clinical value are still under active characterization.