  This study explores the responses to ketamine in patients with
treatment-resistant depression (TRD) using a wearable forehead
electroencephalography (EEG) device. We recruited fifty-five outpatients with
TRD who were randomised into three approximately equal-sized groups (A: 0.5
mg/kg ketamine; B: 0.2 mg/kg ketamine; and C: normal saline) under double-blind
conditions. The ketamine responses were measured by EEG signals and Hamilton
Depression Rating Scale (HDRS) scores. At baseline, responders showed a
significantly weaker EEG theta power than did non- responders (p < 0.05).
Responders exhibited a higher EEG alpha power but lower EEG alpha asymmetry and
theta cordance at post-treatment than at baseline (p < 0.05). Furthermore, our
baseline EEG predictor classified responders and non-responders with 81.3 +-
9.5% accuracy, 82.1 +- 8.6% sensitivity and 91.9 +- 7.4% specificity. In
conclusion, the rapid antidepressant effects of mixed doses of ketamine are
associated with prefrontal EEG power, asymmetry and cordance at baseline and
early post-treatment changes. The prefrontal EEG patterns at baseline may
account for recognising ketamine effects in advance. Our randomised, double-
blind, placebo-controlled study provides information regarding clinical impacts
on the potential targets underlying baseline identification and early changes
from the effects of ketamine in patients with TRD.
