Ketamine and Neurofeedback-Training: Effects on Neuroplasticity in Cocaine Addiction

The goal of this clinical trial is to learn about the effects of the combination of ketamine and realtime functional magnetic resonance imaging (fMRI) neurofeedback training in individuals with cocaine use disorder. The main questions the investigators aim to answer are: * Can the investigators observe a positive, significant effect on percentage of cocaine use days of both interventions combined as well as stand alone interventions? * Is there a significant transfer effect of the neurofeedback training? * Is there a significant, ketamine-dependent change in glutamate levels in the nucleus accumbens? Participants will be given ketamine and a realtime fMRI neurofeedback training. Both interventions are placebo-controlled. The investigators will compare the four intervention groups to investigate the effects of the stand-alone effects of the intervention and the combination of it.

Cocaine is the most frequently used stimulant worldwide, and its consumption rate in Europe indicates a continuing upward trend. Cocaine use is associated with great harms for affected individuals, their families, and the society. Unfortunately, until today no pharmacotherapy has been approved for the treatment of cocaine use disorder (CUD) due to lack of efficacy of tested compounds. The investigators therefore propose, to use latest advancements in proton magnetic resonance spectroscopy (1H-MRS) and real time functional magnetic resonance imaging neurofeedback training (rt-fMRI NFT) to develop a neurobiologically informed experimental approach for an individualized and integrated pharmaco-psychotherapy that has the potential to open new avenues for the treatment of CUD, and in addition, to be transferable to other neuropsychiatric conditions. To improve the efficacy of psychotherapeutic interventions in individuals with CUD, the investigators recently developed an rt-fMRI NFT paradigm based on reward imagery to specifically modify maladaptive reward sensitivity by self-regulating the brain's reward circuits. Furthermore, using a 1H-MRS technique, the investigators recently demonstrated that a disturbed glutamate homeostasis in the nucleus accumbens (NAcc), an important hub in the brain's reward system, characterizes cue-induced craving in CUD. This indicates that urgently needed novel pharmacotherapies for addiction treatment should target the glutamatergic system. Thus, to restore the glutamate homeostasis and to boost learning effect of the reward imagery training, the investigators propose to combine reward imagery rt- fMRI NFT with the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine, which has direct effects both on glutamatergic signaling and neuroplasticity and has shown therapeutic potential to reduce cocaine craving and cocaine us. The investigators anticipate a) restoration of the glutamate homeostasis in the NAcc b) changes in maladaptive reward sensitivity resulting from rt-fMRI NFT and c) synergistic effects of the pharmacological and the psychotherapeutic effect due to the ketamine-induced neuroplasticity that might open a window of opportunity for imagery-based learning. The investigators hypothesize that these neurobiological adaptions induced by the described interventions underlie their therapeutic effects on cocaine craving and use. The effects of ketamine and reward imagery rt-fMRI NFT in individuals with CUD will be tested in a randomized, placebo-controlled, double blind, parallel group study.