Low Dose Intravenous Ketamine in Treatment Resistant Depression Patients

The primary goal of the project is to study the effect of Ketamine on cortical neurophysiological function in Treatment Resistant Depression(TRD) patients. There are three key preclinical findings regarding Ketamine antidepressant effects that motivate the current study: a) low dose Ketamine causes early increase in glutamate neurotransmission; b) Ketamine initiates synaptic plasticity; c) ketamine infusion leads to rapid improvement in depression symptoms. The proposal essentially employs robust and non-invasive neurophysiological techniques, Auditory Steady State Response(ASSR)-gamma oscillatory response and Transcranial Magnetic Stimulation(TMS) cortical excitability to investigate the above findings in patients with treatment resistant depression. Study: Ketamine Infusion: We will employ an open-label study in which the infusion session, the enrolled TRD patients will receive low dose Ketamine (0.5 mg/kg) over 40 minutes. Cortical Excitability: TMS stimulation will be applied to the corresponding region of the contralateral primary motor cortex to determine motor threshold and to examine the motor cortical excitability measures after Ketamine. The optimal coil position will be determined by moving the TMS coil in 1-cm increments over the motor cortical area while delivering single or paired magnetic pulses and by observing maximal contraction of the contralateral abductor pollicis brevis (APB). Electromyography readings will be obtained from the APB muscle. TMS stimulation will then be applied to Left DLPFC or Left Brodmann Area 6 to investigate cortical excitability changes after ketamine. Electroencephalography(EEG) recordings will be concurrent with TMS procedure. ASSR/EEG paradigm: Participants may engage in the auditory steady state response task where click trains of 500-ms duration will be presented binaurally at 65 ± 5 decibel(dB). The click train repetition frequencies will be 40 Hz and presented in the context of an auditory oddball paradigm to ensure participant attention to the stimuli. This task will be done while participants undergo EEG recordings.