Approach-avoidance behavior and motor-specific modulation towards smoking-related cues in smokers.

Abstract

By performing three transcranial magnetic stimulation (TMS) experiments, we measured the motor-specific modulatory mechanisms in the primary motor cortex (M1) at both the intercortical and intracortical levels when smokers actively approach or avoid smoking-related cues. For all experiments, the design was group (smokers versus non-smokers) × action (approach versus avoidance) × image type (neutral versus smoking-related). The study was conducted at the Shanghai University of Sport, CHN, TMS Laboratory. For experiment 1, 30 non-smokers and 30 smokers; for experiment 2, 16 non-smokers and 16 smokers; for experiment 3, 16 non-smokers and 16 smokers. For all experiments, the reaction times were measured using the smoking stimulus-response compatibility task. While performing the task, single-pulse TMS was applied to the M1 in experiment 1 to measure the excitability of the corticospinal pathways, and paired-pulse TMS was applied to the M1 in experiments 2 and 3 to measure the activity of intracortical facilitation (ICF) and short-interval intracortical inhibition (SICI) circuits, respectively. Smokers had faster responses when approaching smoking-related cues (F_1,58  = 36.660, P < 0.001, <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>η</mi></math> _p ²  = 0.387), accompanied by higher excitability of the corticospinal pathways (F_1,58  = 10.980, P = 0.002, <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>η</mi></math> _p ²  = 0.159) and ICF circuits (F_1,30  = 22.187, P < 0.001, <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>η</mi></math> _p ²  = 0.425), while stronger SICI effects were observed when they avoided these cues (F_1,30  = 10.672, P = 0.003, <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>η</mi></math> _p ²  = 0.262). Smokers appear to have shorter reaction times, higher motor-evoked potentials and stronger intracortical facilitation effects when performing approach responses to smoking-related cues and longer reaction times, a lower primary motor cortex descending pathway excitability and a stronger short-interval intracortical inhibition effect when avoiding them.