Ketamine and the Default Mode Network:Helping the Brain Get "Unstuck"

Our brains are constantly active, even when we aren't focused on a specific task. One group of interconnected brain regions, called the default mode network (DMN), becomes particularly active when we are thinking about ourselves, remembering the past, imagining the future, or reflecting on our emotions. This network is an important part of normal brain function, but research suggests that in depression it may become overly rigid or strongly connected to repetitive patterns of negative thinking. This may contribute to rumination—the feeling of getting stuck replaying the same worries, regrets, or negative thoughts over and over.

Ketamine appears to temporarily change the way different brain networks communicate with one another. Brain-imaging studies suggest that ketamine can alter connectivity within the default mode network and between the DMN and other regions involved in emotion, attention, and decision-making. At the same time, ketamine stimulates pathways involved in neuroplasticity, including signaling related to BDNF and the growth and strengthening of connections between brain cells. Rather than simply "turning off" negative thoughts, ketamine may temporarily make patterns of brain activity less rigid and create an opportunity for the brain to develop new ways of processing thoughts and emotions.

This may help explain why the period surrounding ketamine treatment can be valuable for making positive changes. If the brain is temporarily more flexible, activities such as therapy, journaling, exercise, mindfulness, spending time in nature, or reconnecting with supportive people may help reinforce healthier patterns. Ketamine isn't erasing old memories or automatically replacing negative thoughts with positive ones. Instead, one way to think about treatment is that it may help loosen deeply established pathways, giving you an opportunity to practice and strengthen new ones. The medicine may help open the door—but what you do with that opportunity matters.