The Role of Potassium Channels in Working Memory Impairments of Chronic Cocaine Users

Inclusion Criteria: * Current diagnosis of mild, moderate, or severe CoUD according to DSM-5 * Minimum cocaine use of 1g/month in the last three months * Cocaine as the primary drug of consumption * Willingness to abstain from cocaine use at least 72 hours before prior to each study visit * Ability to read, understand and provide written informed consent * To be sufficiently fluent in German * Age between 20 and 50 years * Body mass index (BMI) between 19 and 30 kg/m2 * If applicable: luteal phase of the menstrual cycle * For individuals with childbearing potential: use of contraceptive measures Exclusion Criteria: * Presence or history of severe neurological disorders or head injuries * Current diagnosis of an acute or chronic infectious disease * If applicable: pregnancy and breastfeeding * Lifetime history of any epileptic seizures * Lifetime diagnosis of a cardiovascular disease, specifically arrhythmia and long QT syndrome * Clinically significant laboratory or ECG abnormality that could be a safety issue in the study * Lifetime diagnosis of liver or kidney disease including moderate or severe renal impairment (creatinine clearance \< 50 ml/min) * Known hypersensitivity or allergy to 4-aminopyridine * Use of potassium channel blockers within the last 3 months * Use of psychotropic medication within the last 7 days * Use of inhibitors of the organic cation transporter 2 (OCT2), such as cimetidine * Lifetime diagnosis of schizophrenia, bipolar disorder, obsessive-compulsive disorder, or autism spectrum disorder according to DSM-5 * Diagnosis of a current episode of depression * Current diagnosis of a moderate or severe substance use disorder other than CoUD according than DSM-5 * Daily cannabis consumption in the past three months * (E-Cigarette) Fagerström Test of Nicotine Dependence Score \> 5 (strong nicotine dependence) * Inability to follow the procedures of the study, e.g., due to language problems * Being related to or in any form dependent on the investigator * Prior participation (less than two years ago) in a study investigating working memory using the n-back task, the SWM, PAL, RVP, or LNST * Participation in another study with investigational drugs within the 30 days preceding and during the present study