The effects of non-invasive brain stimulation of the tongue muscle cortical representation on tobacco addiction.

Material Transcranial direct current stimulation In this project we propose to modulate the excitability of the cortical representation of the tongue muscle through a non-invasive brain stimulation method, namely transcranial direct current stimulation (tDCS), to explore effects on reward-related behaviours. tDCS is an established investigative tool in the cognitive neurosciences and psychiatry permitting safe and non-invasive stimulation of the subjacent cortex. tDCS modulates cortical excitability using small direct electrical currents (1 ~ 2 mA) passed through the brain (e.g., Nitsche & Paulus, 2000, J Physiol) via two electrodes with opposite polarities (i.e., anodal and cathodal) placed on the scalp. Anodal (A) stimulation increases cortical excitability, whereas cathodal (C) stimulation decreases it (Stagg and Nitsche, 2011, Neuroscientist). These effects can last for up to 90 min after a single stimulation session of 13 ~ 20 min (Nitsche and Paulus, 2001, Neurology), and can be further extended by repeated stimulation (i.e., cumulative effects) (Monte-Silva et al. 2013). In the present projects, a direct current of 2 mA intensity will be delivered for 20 minutes per session by a battery-driven, constant-current stimulator through two saline-soaked surface sponge electrodes. Previous studies have shown that this intensity of stimulation is safe in healthy volunteers (Nitsche et al., 2003, Clin Neurophysiol). Procedures Participants 15 participants will be recruited from the University of Tasmania. All participants will be assigned, in separate sessions to one of three stimulation conditions: Cathodal, Anodal, Sham. The stimulation order will be counterbalanced across participants. Measures During a baseline session, carbonmonoxide (CO) in expired air will be taken as an objective measure of recent smoking, and a level > 15 ppm will be considered as consistent with recent smoking, and will serve as further exclusion criterion. Before and after the tDCS session participants will be submitted to a craving assessment, including the completion of the Fagerstrom Test for Nicotine Dependence, Urge to Smoke (UTS) Scale and a self-report rating via Visual Analogue Scale (VAS). Moreover, they will be submitted to the Profile of Mood States (POMS), questionnaires for smoking history and demographic information. To induce craving, participants will be also asked to watch 25 pictures of smoking cue immediately before each craving assessment session. As further measure for tobacco consumption, participants will be tested for urinary cotinine concentrations. Who will deliver the intervention? The intervention will be delivered by Dr. Carmelo Vicario. Carmelo is Research Fellow at the University of Tasmania. He has extensive research experience (i.e., 12 years) in the field of Cognitive, Clinical and Social neuroscience. He has a PhD in Neuroplasticity and rehabilitation of Cognitive functions and in the use of non-invasive brain stimulation methods. In the last 4 years Dr. Vicario has conducted a successful research programs for the study of tobacco addiction and reward system in healthy humans through the use of a non-invasive brain stimulation method such as the Transcranial magnetic stimulation. In particular, he has studied the contribution of the Tongue motor cortex neurons in detecting changes in the activity of reward system. These results suggest that this pool of motor neurons is sensitive to changes in the activity of reward system. The results of this research program have been published in important scientific journals (i.e., The Journal of psychiatry and Neuroscience) and represent the key platform for the proposed trial, which intend to test the effects of non-invasive stimulation of the cortical representation of the tongue muscle on tobacco addiction. The mode of delivery All participants will be tested under nicotine abstinence. A direct current will be delivered by a battery-driven, constant-current stimulator (Neuroconn) through two saline-soaked surface sponge electrodes. Each participant will be tested in two sessions, at least 48h apart. They will be stimulated at a different types of stimulation in each session with the order of stimulation counterbalanced across sessions. The MTA [(a scalp region located 1.5 cm posteriorly to the area 44, as suggested by Uozumi et al. (2004) Neurology] will be identified via EEG 10-20 International system; The tDCS will be applied over the target scalp regions for 20 minutes. The return electrode will be placed over the left shoulder. We will compare the participants’ craving symptoms before and immediately after each single session of tDCS. Participants will be asked to smoke their last cigarette at least 10 hours before the experimental session. Each session will consist of the following steps: i) we will collect (daily) urine sample to quantify the urinary cotinine concentrations which would provide a more reliable measure of the tobacco consumption in the 48 hours following each tDCS session; ii) we will confirm that the participant has not smoked for at least 10 hours by measuring breath carbon monoxide (Micro Smokerlyzer); iii) exposure to smoking cues; iv) Questionnaires for smoking history and demographic information will be completed to quantify subjective craving and other related parameters; v) tDCS session; vi) The previous questionnaire will be repeated. The location where the intervention occurs: University of Tasmania, Division of Psychology, School of Medicine, Psychology research center, Sandy Bay, Hobart, 7005, TAS.