Table 1.

Comparison of several potential biomarkers for the closed-loop DBS

Biomarker	Stability	Invasiveness degree	Capability to merge stimulation/recording electrodes	Patient friendliness	Spatial resolution	Applied diseases
Neuro-electrophysiological biomarkers
EEG potentials	High noise and artifacts sensitivity	Non-invasive	No, needs separate recording and stimulation electrodes	No damage to the head	Poor, ~3–9 cm [38]	PD [29]
ECoG potentials	Moderate noise and artifacts sensitivity	Least invasive	No, needs separate recording and stimulation electrodes	Minor damages to the skull and Dura matter	Moderate, ~0.5 cm [38]	PD and Epilepsy [23]
LFP potentials	Long-term stability [48]	Invasive	Yes, same recording and stimulation electrode [84]	Some neuronal and vasculature damages	High, ~1 mm [38]	PD [3, 12], Epilepsy [86]
AP potentials	Need recalibration for good stability [44], less practical for long-term sue	Most invasive	No, needs separate recording and stimulation electrodes	Extra neuronal and vasculature damages	Very High, ~0.2 mm [38]	PD [2]
Other biomarkers
EMG potentials	High noise and artifacts sensitivity	Non-invasive [31, 32]	No, needs separate recording and stimulation electrodes	No damage to the head	Poor [150]	Movement disorders [30, 33]
Biochemical potentials	Require short time for stabilization of carbon-fiber micro-electrode during recording [45]	Invasive	No, needs separate recording and stimulation electrodes [151]	Some neuronal and vasculature damages	High [152]	Essential tremor [153], and depression [154]