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Neural Systems, Inhibitory Control, and Methamphetamine Dependence

The Neural Systems, Inhibitory Control, and Methamphetamine Dependence study started in 2011 and is currently finishing data collection for its last participants. The study included methamphetamine abusing individuals and healthy control participants aged 18-55 years. Participants who qualified over the telephone were scheduled to visit the London Laboratory at the UCLA Semel Institute for Neuroscience and Human Behavior for the In-Person Screening Phase. The screening procedures, usually scheduled over two visits, determined if participants were eligible to complete the subsequent study visits. Both groups completed identical screening procedures, with the exception of more in-depth drug use questions for the methamphetamine users.

After providing written consent, participants completed questionnaires about their mood, medical, psychiatric and drug use history, personality and life experiences. They also provided a urine sample to determine what drugs they recently used and a breath sample to determine the carbon monoxide levels in their system. The drug screen tested for recent methamphetamine, cocaine, opiates/opioids, benzodiazepines, THC and other amphetamines. Methamphetamine participants needed to test positive for methamphetamine at admission. If methamphetamine participants tested positive for any drugs other than methamphetamine or marijuana, and if healthy control participants tested positive for any drugs other than marijuana, they were excluded from the study. Additionally, the urine samples of female participants were tested for pregnancy; pregnant females were also excluded. If no exclusionary criteria were met during the first screening visit, participants completed a second screening visit to ensure they were mentally and physically healthy enough to participate. The second screening visit included a psychiatric diagnostic interview (DSM-IV (SCID-I) for first 500 participants and the MINI International Neuropsychiatric Interview M.I.N.I for the last 50 participants). Additionally, laboratory tests and procedures were completed by the UCLA General Clinical Research Center and interpreted by a study physician. Laboratory tests included vital signs (heart rate--BPM, blood pressure, and respirations), an electrocardiogram (ECG) to record the electrical activity of the heart, and an 18-cc blood sample to perform laboratory tests which included a complete chemistry and metabolic panel, hepatic panel, Hepatitis-C tests, and HIV test. The laboratory tests from this blood sample ensured that participants' liver and kidneys were functioning normally, and that their standard blood counts (red cell, white cell, and salts) were also normal. If a Hepatitis-C (HCV) or HIV test was positive, participants were not allowed to continue in the study and their results were reported to the California State Health Department.

Participants deemed eligible to continue in the methamphetamine group participated on an outpatient basis or were admitted to the UCLA Medical Center to participate on an inpatient basis for up to 10 days. Typically, detectable levels of methamphetamine in urinalysis remain for 2-3 days, therefore inpatient days 0-3 served as a "washout period" and the methamphetamine abusing inpatient participants provided daily urine samples to test for recent drug use and pregnancy (female participants only). Outpatient participants were also required to remain abstinent from all drugs except nicotine and marijuana for at least 4 days prior to study sessions. Self-reported abstinence for outpatients was verified by urine toxicology and saliva screening at every visit to UCLA before completion of study procedures.

Neurocognitive assessments, about three hours each, typically took place on two separate days. The purpose of the neurocognitive sessions were to assess participants' intellectual and neurocognitive functioning. On either the same day as the neurocognitive testing or on separate days, both methamphetamine abusers and healthy controls were administered a structural MRI to collect information on brain structure.