Subjects: Fourteen healthy non-smokers and 14 non-smokers with SCZ will complete this exploratory study. This sample size is based on a previous study that used the TMS-EEG method and demonstrated a significant difference in cortical inhibition between healthy controls and SCZ patients[10], and will be sufficient to detect a medium effect size (Cohen´s d=0.72; α=0.05, 1-β=0.80) of nicotine treatment. Only patients that are treated with a stable dose of antipsychotic medication (≥1 month) will be enrolled in this study. This could potentially confound the results as the investigators are using healthy non-medicated controls for comparison. However, the within- subjects design is an effort to control for such effects. Study design: The study will be a double-blinded, placebo-controlled, crossover study consisting of two PAS-25 testing sessions one month apart, followed by a 7 day post-PAS follow-up test session each. Pharmacological treatment: Nicotine (4 mg) or matching placebo gum will be administered on each of the two test days before baseline TMS-EEG recording. Maximum nicotine blood concentration is reached after 30 min, at which point blood samples will be drawn to assess nicotine levels. WM assessment: The N-back task measures the ability to maintain active information online (i.e. WM) and is dependent on DLPFC functioning. Letters are presented in a continuous sequence and the subject is asked to respond if they recognize the present letter as the same letter appears that appeared as the N (0, 1, 2 or 3) letters back, i.e. "N-back". The N-back will be administered at the pre-test training session (to control for training effects), baseline, 120 minutes and 1 week post PAS. Paired Associative Stimulation (PAS): The pairings will occur over a 30 min period and the peripheral nerve stimulation and TMS to the DLPFC will be delivered at 0.1 Hz. To assure the DLPFC localization, neuronavigational techniques using the MRIcro/reg software and a T1-weight MRI scan will be used. Quantifying LTP: To assess DLPFC LTP, change in cortical evoked activity will be measured using pre- and post-PAS TMS-EEG recordings. TMS pulses will be generated using two Magstim 200 stimulators (Magstim Company Ltd., UK) connected to and a 7 cm figure-of-eight coil via a Bistim module. A train of 100 pulses (0.1 Hz) will be administered together with EEG recordings; (1) before PAS in order to assess baseline cortical evoked activity and (2) at different time points (0, 15, 30, 60,120 min and 7 days) following PAS-25. EEG will be recorded using the DLPFC-corresponding electrodes of a 64-channel Synamps 2 EEG system. Cortical evoked activity will be defined as the area under the rectified curve for the averaged EEG recordings (50-275 ms post-stimulus) and LTP will be quantified as the change in cortical evoked activity from baseline. Statistics: Within and between subjects comparisons will be carried out using repeated measures, mixed-factorial, ANOVAs when appropriate. Relationship between LTP and nicotine levels will be assessed using Pearson correlations. P-values will be set to 0.05 and multiple comparisons will be Bonferroni corrected.