The primary goal will be to identify the optimal pulse protocol by systematically measuring the efficacy of various theta burst stimulation and repetitive rTMS protocols to increase and decrease the reward positivity in dependent smokers. The secondary objective will be to measure the protocols' effectiveness to increase decision-making capacity using the probabilistic selection task (PST). The third objective will be to specifically assess whether the TMS targets has a differential impact on state levels of craving relative to baseline (Tobacco Craving Questionnaire \[TCQ\]. The investigators plan to accomplish these three objectives using a randomized, controlled experiment involving 2 sessions.
Nicotine dependent individuals (according to the Alcohol, Smoking and Substance Involvement Screening Test nicotine dependence score).
Be between the ages of 18 and 55 years old.
Not received substance abuse treatment within the previous 30 days.
Be in stable mental and physical health.
Contraindication to MRI (e.g., presence of metal in the skull, orbits or intracranial cavity, claustrophobia).
Contraindication to rTMS (history of neurological disorder or seizure, increased intracranial pressure, brain surgery, or head trauma with loss of consciousness for > 15 minutes, implanted electronic device, metal in the head, or pregnancy).
History of autoimmune, endocrine, viral, or vascular disorder affecting the brain.
History or MRI evidence of neurological disorder that would lead to local or diffuse brain lesions or significant physical impairment.
Parallel
Transcranial Magnetic Stimulation
DeviceTMS will be delivered using a robotic neuronavigation system (Smartmove, ANT). Stimulation intensity will be standardized. Stimulation will be delivered to the L-DLPFC using a active/placebo figure-8 coil and a magventure TMS device.
Event-related Brain Potential: Reward Positivity
The reward positivity is an event-related brain potential (ERP) sensitive to reward feedback. The reward positivity will be measured during the T-maze task, where participants will receive feedback (Reward, No-reward) following choices. ERPs will be created for each electrode and participant by averaging the single-trial EEG according to feedback type (Reward, No-reward). The reward positivity will be evaluated by subtracting the Reward feedback ERPs from the corresponding No-reward feedback ERPs. The size of the reward positivity will then be determined by identifying the maximum absolute amplitude of the difference wave within a 200-to 400-msec window after feedback onset and evaluated along electrodes Fz, FCz, and Cz. The reward positivity will be measured for each pulse protocol across condition 1a and condition 1b of dependent smokers. The reward positivity will be used to measure the efficacy of the pulse protocol to modulate reward activity.
Approach Learning
Approach learning will be measured using a Probabilistic Selection task (PST), in which subjects are shown pairs of arbitrary stimuli and must learn by trial-and-error to select one of each pair. During an initial learning phase participants are exposed to three pairs of stimuli, each of the three pairs is rewarded on 80%, 70%, and 60% of the trials. Subjects learn by feedback that some stimuli are associated with more positive feedback (Approach) and that some stimuli are associated with more negative feedback (Avoidance). To determine whether subjects learn more from positive (approach) or negative (avoidance) feedback, during a subsequent testing phase they are required to choose between novel stimulus pairs. Approach learning (accuracy and reaction time) for each proposed pulse protocol across condition 1a and 1b will be measured during the testing phase. Avoidance learning performance will be used to measure the efficacy of the pulse protocol to modulate decision making.
Nicotine Craving
The level of craving will be assessed in dependent smokers using the short version of the Tobacco Craving Questionnaire (TCQ), a 12-item scale that assesses state levels of craving. TCQ will be measured at the start of each session, and following each TMS protocol (once for each pulse protocol). The investigators will compared the TCQ score from pre-TMS (start of session) to post-TMS.
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