Controlling Pupil Size to Influence Arousal and Emotion

Arousal is a fundamental part of how our brain keeps us alert, engaged, and responsive to the world around us. It is controlled by networks deep in the brainstem, like the locus coeruleus (LC), which help set our mental and physical states for tasks that need focus or quick reaction. Interestingly, one outward sign of arousal in the brain is pupil size. Scientists have long known that pupil size can reflect brain arousal levels, but Meissner et al. (2024) took this further by showing that, with training, people can actively control their pupil size. This biofeedback approach taps into an intriguing possibility: could self-regulating pupil size open new doors to managing our own arousal and even stress responses?

Pupil Biofeedback: A Window into the LC and Beyond

Using biofeedback, Meissner et al. trained participants to increase and decrease their pupil size using different mental strategies—such as imagining relaxing scenes or exciting, energizing situations. Remarkably, after just three days, participants could reliably shift their pupil size up or down, even without constant feedback, demonstrating a sustained skill. This process of pupil self-regulation turned out to activate the LC and other brainstem regions tied to arousal. Participants also effectively changed their body's physical responses, such as heart rate, pointing to a broader impact on autonomic functions.

Implications for Emotional Health

What makes this research particularly compelling is its potential to translate into therapeutic applications. Stress-related and anxiety disorders often involve heightened arousal states, which can make relaxation and focus challenging. The study hints that training individuals to regulate arousal through pupil biofeedback could offer a non-invasive way to manage symptoms. The findings also suggest that when we can modulate arousal, we might better control related physiological responses, such as heart rate, which are often altered in stress-related disorders.

Connecting Back to Self-Regulation Techniques

This research not only opens a scientific window into the mechanics of arousal but also validates the efficacy of biofeedback techniques. Practices like mindfulness, breathwork, and meditation have long been used to influence emotional well-being through body-brain connections. By enhancing awareness of our physiological states—such as with subtle shifts in pupil size—we might gain new insight into how seemingly small bodily signals can profoundly shape our mental state.