Long, deliberate exhales slow your heart rate via a specific circuit from a known brainstem nucleus through your vagus nerve. We can thank the amazing Jack Feldman from UCLA for much of our understanding of the brain circuits that control breathing and heart rate.

Note: Yes, light plays a role in color, but this effect is about more than just color. It involves how neighboring receptive fields influence one another, as well as adaptation phenomena in neurons. Visual illusions have taught us a lot about how the neural retina and visual system work.

We’ve created a series of zero-cost, no-sign-up newsletters that summarize these protocols. You can sign up for more if you want, but you don’t need to. All are available here: hubermanlab.com/newsletter. Enjoy!

Just remember: That friction is the gateway to self-directed plasticity. It reduces the number of trials required to learn. No friction, no learning—unless it’s something that naturally excites and focuses you.

The ideal scenario is one in which the thing you want to learn evokes catecholamine release. That requires natural excitement, focus, and a resulting state shift. Most adult learning is not like that. Most involves self-directed focus—a “friction” of sorts.

The catecholamines—dopamine, epinephrine, and norepinephrine—are major “state-shifting” neuromodulators that underlie the “state/change + experience = plasticity” effect. There are behavioral and pharmacologic ways to alter their levels. Many of the prescription and illicit methods are addictive.

While it depends on the pathway, a major determinant of plasticity rate is the degree of brain and bodily state shift that occurs.