I want you to imagine that your significant other just broke up with you. You are sitting on your couch at home, ruminating about all of the “mistakes” that you made leading up to the break up. Considering that one of the biggest predictors of depression and anxiety is a pattern of self-blame and rumination (1), you will likely not be surprised by the feeling of sadness that arises as you obsess.
Now I want you to imagine that you had attended a mindfulness seminar the week before this break up where you had learned about mindful breathing. You recall the existence of this new skill and direct your attention towards your breathing.
You naturally slow your breathing as your focus deepens and you notice the sensation of coolness on the tip of your nose during inhalation. You notice the gentle rise and fall of your abdomen. You notice the subtle to-and-fro beat of your heart in your chest. Importantly, you don’t notice any thoughts related to the break up during your times of peak focus.
What has happened in your brain during these two stages of consciousness?
To answer this question, we must introduce two opposing networks in the brain known as the default mode network (DMN) and the task-positive network (TPN). These two networks are like the on/off position of a light switch in that the activation of one by definition inhibits the other (2).
The DMN is labeled “default” because it represents the mind in a neutral state without a mental or physical focal point (2). The DMN is the network that allows us to daydream, remember, and imagine. It is unstructured.
The TPN on the other hand becomes active when we have a mental or physical task that we are willfully engaging with (3). The TPN is engaged when we focus on external or internal sensations, make plans, or perform complex physical tasks.
Let’s break the two networks down further.
The DMN consists of four parts of the brain: amygdala, hippocampus, posterior cingulate cortex (PCC), and medial prefrontal cortex (mPFC) (4).
In our rumination example, your amygdala and hippocampus recall the stored memories from your ill-fated relationship. The amygdala produces the emotional color while the hippocampus sketches the so-called factual elements. The PCC synthesizes the raw sensory, factual, and emotional data from the breakup memory into a complex parcel of information ready for conscious experience. Finally, the mPFC assimilates all of the information into a cognitive form, generating thoughts of self-blame, hypothesized cause-and-effect, and explanatory models.
The TPN consists of another four neurological structures: insula, somatosensory cortex, anterior cingulate cortex (ACC), and dorsolateral prefrontal cortex (dlPFC) (2).
When you decide instead to focus on your breath, the insula provides the internal sensations of your heartbeat and breathing while the somatosensory cortex furnishes the external sensation of coolness at the tip or your nose. The ACC acts as a prism, focusing the intention of your dlPFC to attend to the aforementioned internal and external sensations.
The details of the DMN and TPN are less important than is the fact that the DMN and TPN are effortlessly mutually exclusive. The relationship between the DMN and the TPN is analogous to the relationship between inhalation and exhalation: despite their intimate nature, the two cannot exist simultaneously.
Thus, rather than binding oneself in the mental straightjacket that is battling thought with more thought, you can simply engage fully in a mental or physical activity. In doing so you will interrupt your ability to ruminate by sheer biological constraint. You only have the mental power to run a single network. Overcoming the DMN is not a matter of pushing through a mental barrier so much as it is a simple matter of bypassing the barrier altogether.
Returning to our light switch analogy, it is important to remember that our attention is fickle and the oscillation between DMN and TPN resembles the frantic flicker of a light switch in the hands of an overeager toddler. You will focus intently on your breath, engaging the TPN, only to be interrupted the next second by the return of a ruminative thought as the DMN takes over and the TPN goes dark.
As with most things, practice makes perfect – or more perfect. You practice meditation to strengthen your TPN so that you might have longer stretches of attentional focus before the DMN interjects with wayward thought.
Your brain evolved to balance the DMN and TPN. The DMN was an excellent mental simulator for reviewing or imagining past or future hunts. While the TPN allowed complete immersion in complex physical or mental tasks.
However, in modern cerebral humans overactivity in the DMN is associated with depression and anxiety (5). The practice of mindfulness involves learning how to restore this natural balance in a world that favors the DMN.