Thus pupil size self-regulation links to fundamental changes in brain function, which opens many questions of how pupil-based biofeedback could be applied in future clinical applications in psychiatric and neurological conditions.

Upregulation of pupil size was linked to increased cortical excitability and arousal, increased heart rate and reduced HRV compared to pupil size downregulation. P300 amplitudes were larger during down- than upregulation.

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In three experiments we show that volitional up- and downregulation of pupil size modulates

1) cortical excitability, as measured by TMS evoked motor evoked potentials ⚡
2) the 1/f spectral slope, a marker of cortical arousal 🧠
3) heart rate and HRV 🫀
4) the P300 in an oddball task 🔊