What goads cigarette smokers to smoke? Neural adaptation and the mirror neuron system.
One model of addiction suggests that neural circuits in the frontal cortex adapt to drug use and become sensitized leading to excessive attribution of incentive salience to drug-associated cues. The present study examined changes associated with cigarette use in the frontal mirror neuron system (MNS) of the human brain, as reflected in mu rhythm responsiveness. Mirror neurons in premotor cortex exhibit visuomotor properties that allow them to respond to self-movement as well as the observation of movement. This is a potential neural substrate for imitation learning and social cognition, factors that may be important in determining who does and does not develop addictive behaviors. EEG mu rhythm suppression is hypothesized to reflect MNS activity and thus provide a non-invasive method for studying this relationship. Our results show that while nonsmokers exhibit normal mu suppression to observed and self-generated actions, smokers exhibit normal suppression only to self-movement but not to the observation of movement, particularly actions involving addiction-related cues. Non-abstinent and abstinent smokers (those abstaining for approximately 12 h) did not differ significantly in their responses to the observation of movement, i.e., both exhibited atypical patterns of mu rhythm reactivity compared to nonsmokers. These data support the hypothesis that cigarette use produces short- and longer term adaptations in the MNS. Such adaptations may inappropriately bias attention toward motivationally salient, addiction-related cues leading to more impulsive and addiction-related behaviors.