Automatized smoking-related action schemata are reflected by reduced fMRI activity in sensorimotor brain regions of smokers

Abstract

In the later stages of addiction, automatized processes play a prominent role in guiding drug-seeking and drug-taking behavior. However, little is known about the neural correlates of automatized drug-taking skills and drug-related action knowledge in humans. We employed functional magnetic resonance imaging (fMRI) while smokers and non-smokers performed an orientation affordance task, where compatibility between the hand used for a behavioral response and the spatial orientation of a priming stimulus leads to shorter reaction times resulting from activation of the corresponding motor representations. While non-smokers exhibited this behavioral effect only for control objects, smokers showed the affordance effect for both control and smoking-related objects. Furthermore, smokers exhibited reduced fMRI activation for smoking-related as compared to control objects for compatible stimulus-response pairings in a sensorimotor brain network consisting of the right primary motor cortex, supplementary motor area, middle occipital gyrus, left fusiform gyrus and bilateral cingulate gyrus. In the incompatible condition, we found higher fMRI activation in smokers for smoking-related as compared to control objects in the right primary motor cortex, cingulate gyrus, and left fusiform gyrus. This suggests that the activation and performance of deeply embedded, automatized drug-taking schemata employ less brain resources. This might reduce the threshold for relapsing in individuals trying to abstain from smoking. In contrast, the interruption or modification of already triggered automatized action representations require increased neural resources.

Fig. 1

A. Reaction times (means and SEs) of the two groups (smokers vs. non-smokers) for the two object categories (smoking objects vs. control objects) (main effect of compatibility p = 0.01) B. Affordance indices (means and SEs) of the two groups (smokers vs. non-smokers) for the two object categories (smoking objects vs. control objects). Error bars indicate SE from the mean; *p < 0.05., n.s. t-test not significant.

Fig. 2

A whole-brain RFX ANOVA interaction “object category × compatibility × group” revealed significant activations in several brain regions. ROI-based within subjects ANOVAs for smokers showed in right primary motor cortex (A) and right cingulate gyrus (B) higher fMRI activations for control objects in the compatible condition, whereas in the incompatible condition higher fMRI activations were observed for smoking objects. Similar activation patterns were revealed in left fusiform gyrus (C) and right middle occipital gyrus (D). The scale on the left side indicates minimum and maximum F values, the degrees of freedom, and the significance level for the interaction. Corrected for multiple comparisons using the cluster-size thresholding (1000 iterations, α = 0.05). Error bars indicate SE from the mean; *p < 0.05.