Identify the Optimal TMS Target to Modulate Reward Activity

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 proposed DLPFC target across active and sham groups of dependent smokers. The reward positivity will be used to measure the efficacy of the DLPFC target 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 DLPFC target across active and sham groups will be measured during the testing phase. Avoidance learning performance will be used to measure the efficacy of the DLPFC target to modulate decision making.

Avoidance Learning

Avoidance 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. Avoidance learning (accuracy and reaction time) for each proposed DLPFC target across active and sham groups will be measured during the testing phase. Avoidance learning performance will be used to measure the efficacy of the DLPFC target 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 Block of TMS (once for each DLPFC target). We will compared the TCQ score from pre-TMS (start of session) to post-TMS.