Investigation of the Influence of Transcranial Direct Current Stimulation (tDCS) on the Brain Activation Measured by fNIRS During the Decision Not to Smoke in High-risk Situations

Dependent smokers will be measured in the morning, adjusted to the usual time of getting up or a minimum 4-hour abstinence period. All participants will be measured on two days:

Day 1: First, after written consent to participate in the study, all inclusion and exclusion criteria are checked and standardized questionnaires are collected. To validate the activity in the dorsolateral prefrontal cortex (dlPFC) and in the orbitofrontal cortex (OFC) individually, two "localizer measurements" are performed. For the dlPFC, a go/nogo task will be used with smoke-associated and positive images; for the OFC, the same images from the dlPFC localizer will be used and viewed in a "passive viewing task" that will be pushed away by keypress.

Next, a modified version of a cue exposure follows for 5 min that has already been implemented in preliminary studies (Kroczek et al., 2016, 2017). All smokers have their own cigarettes, a lighter, and an ashtray on a table in front of them. The cue-exposure is done twice, once in a laboratory room and once in a naturalistic smoking setting. This condition is used as training for the Support Vector Machine (SVM).

This is followed by a cue exposure in which smokers are allowed to actually decide whether to smoke a cigarette or to resist. This condition occurs only outside, after the first part of the experiment has taken place. In this "50% condition", participants receive the instruction that they are allowed to take a drag on their cigarette after each prompt and they should take a drag in about half of the trials. Smoking behavior (puff on the cigarette/no puff on the cigarette) and also craving is noted by the experimenter.The goal of the first day is to train the SVM to detect maximum cue-reactivity concurrent to its cognitive control by response inhibition

Day 2: At most one week after time point 1, the SVM will be used to promote the cortical activity state that enables effective cue exposure therapy during the exposure condition in the smoking risk situation. With the aid of SVM, a tDCS intervention should be triggered at the optimal moment to further solidify extinction learning. This cue exposure measurement is used to classify successful inhibition of smoking. The measurement will take place in the naturalistic setting outside and the participants are NOT allowed to smoke but should increase their craving. As soon as the desired activity state is reached, indicated by the SVM, but at the latest after 5 minutes, tDCS is applied.