Transcranial Magnetic Stimulation Used to Both Measure Cortical Excitability and Explore Methamphetamine Cue Craving

Specific Primary Aims include: Aim # 1. The investigators explore the feasibility of using the TMS to investigate the cortical excitability and to inhibit meth cue craving in meth dependent population. The investigators anticipate that meth elevates cortical excitability measured by motor threshold, causes changes of cortical silent period, and RC. The investigators also anticipate that paired pulse measures (short-interval intracortical inhibition, short-interval intracortical facilitation and long-interval intracortical inhibition) will be different from healthy control, which are more directly linked to glutamatergic cortical facilitation and GABAergic inhibition, respectively. Aim # 2. Given the change of the cortical excitability in meth users, the investigators will use inhibiting TMS (1 Hz) over medial prefrontal cortex to study whether TMS can be used to reduce cue craving. The investigators hypothesize that repetitive TMS reduce meth cue craving in meth dependent population compared with sham rTMS.