The default mode network (DMN) is a set of brain regions active during rest and self-referential thought. This review of studies up to August 2016 examined how DMN functional connectivity varies in healthy people by age, sex, cognitive function, and analysis method. DMN connectivity follows an inverse U-shape across the lifespan: strongest in adulthood, lowest in children and the elderly. Cognitive function positively correlates with DMN connectivity. Females show stronger intranetwork connectivity than males. Effects of analysis type were inconclusive. A voxel-wise meta-analysis for age confirmed an immature network in children versus adults and a stronger network in adults versus the elderly. Defining normal variation may help identify DMN changes in pathology.
The psychostimulant MDMA (ecstasy) causes degeneration of serotonin nerve endings in the forebrain of rodents, nonhuman primates, and human users. To study this in a large animal without using primates, researchers used PET scans to map serotonin transporters and 5HT1A receptors in the brains of Göttingen minipigs before and after MDMA treatment. Total doses above 20 mg/kg reduced serotonin transporter binding: a mean 42 mg/kg dose caused a 32% decrease in the midbrain and thalamus and a 53% decrease in forebrain structures. This loss did not consistently alter 5HT1A receptor binding. The number of serotonin-producing neurons in the dorsal raphé nucleus (about 95,000 in normal animals) remained unchanged.
LSD reduces the binding potential of a dopamine D2/3 receptor tracer in the striatum of pigs, suggesting a direct interaction with these receptors. In a PET study, the binding potential of [11C]raclopride decreased by 19% four hours after LSD administration, without changes in cerebral blood flow. In vitro experiments showed LSD displaces the tracer from pig brain tissue with an IC50 of 275 nM, and a two-site model indicated a subnanomolar component comprising 20% of binding. Microdialysis in rats found no changes in dopamine or its metabolites. These findings indicate LSD directly occupies a portion of dopamine D2/3 receptors, which may contribute to its psychoactive effects.
A proof-of-concept randomized controlled trial will test whether a 4-week mindfulness-based intervention, added to treatment-as-usual, improves anxiety, emotion regulation, and interoception in 50 postpartum mothers with anxiety disorders. The intervention is adapted from Mindfulness-Based Cognitive Therapy and delivered virtually. Self-report measures will be collected at baseline, post-intervention, and at a 3-month follow-up; resting-state functional MRI will be conducted at baseline and post-intervention. The authors hypothesize improvements in anxiety, emotion regulation, and interoception, along with decreased default mode network and increased salience network connectivity. This is the first study to examine combined psychological and neural effects of mindfulness in postpartum anxiety disorders.