This observation supports and extends the conclusions about compromised activity in the Salience Network nodes (Seeley et al, 2007) described in occasional cannabis users following the smoking of a single joint of cannabis (Battistella et al, 2013). The key role in this network is played by the insula, a region involved in subjects' awareness of error, in the processing of affective and internal information and in switching between the different brain networks. Changes in this structure have also been confirmed in alcohol addiction where the decrease in insular activation seems to reflect an inability to switch from interoceptive cravings to cognitive control for suppressing internal needs (Sullivan et al, 2013). Here we complement this finding of functional change with its structural substrate. On the other hand, the activity in other nodes of the Salience and the Control Executive networks (VMPFC, ACC, Dorsolateral Prefrontal cortex) that is compromised in occasional smokers is not associated with structural changes in these regions in regular cannabis smokers. It remains thus to be explored whether morphological variations in these areas may occur at a later stage or in the presence of more serious addiction-related behaviors that our participants do not exhibit.
