The brain's default mode network (DMN) is linked to self-referential thought during rest, but it also serves other functions, and self-reference involves regions outside the DMN. In 88 participants, self-referential and resting-state brain activity were compared to identify DMN areas common to both conditions that also show specialization for self-reference. The 'core-self' DMN regions—medial prefrontal cortex, posterior cingulate cortex, and inferior parietal lobule—were analyzed with dynamic causal modeling. The optimal model indicated that self-related processes are driven by posterior cingulate activity and moderated by the medial prefrontal cortex. This confirms these regions' importance for self-reference and clarifies their specialized roles.
Chronic cannabis use is associated with reduced motivation, and this study examined how it affects functional connectivity between the basal ganglia and brain regions involved in internal (frontal cortex) and external (sensory cortices) motivation signals. Resting-state fMRI in 28 chronic cannabis users and 29 controls showed that cannabis exposure attenuated the positive correlation between the striatum and limbic frontal-basal ganglia circuits, and attenuated the negative correlation between the striatum and the fusiform gyrus, which is important for recognizing significant visual features. These connectivity alterations were linked to lower arousal in response to affective pictures. Changes tended to normalize after one month of abstinence, indicating that cannabis impairs fine-tuning of the motivation system, but this effect is reversible.