From Neuroscience of Mindfulness: Default Mode Network, Meditation, & Mindfulness, an overview of basic brain structures and networks.
The key points listed at the end of the article (note: DMN = Default Mode Network, the wandering mind network, and TPN = Task Positive Network, focused or mindful):
An overactive DMN is highly correlated with negative mood states and certain mental illnesses.
The DMN can be simplistically conceptualized as a ruminative network. It directs our awareness to the past and future while largely ignoring the present. And while the DMN can be used responsibly to plan and organize, we must always be wary of its runaway force.
The TPN is involved in present moment awareness.
The TPN is engaged when we attend to the here and now. It is the action network. The TPN is our direct line to mindfulness and the Present Moment in which worry and sadness cannot survive.
The TPN and DMN are mutually exclusive.
By activating the TPN we deactivate the DMN. This may be the most powerful lesson of our entire discussion. The next time you feel helplessly lost in worry or self-recrimination remind yourself of the power of the TPN. Go for a walk, practice yoga, sense your breath, or engage fully in a conversation with a friend. You need not overpower your DMN to escape negative thoughts. You need only to intentionally engage your TPN and allow your natural physiology to disengage your DMN.