Spontaneous pupillary oscillations increase during mindfulness meditation

A significant body of literature has shown that pupil size varies with cognitive and perceptual states [1Mathôt S. Van der Stigchel S. New light on the mind's eye: the pupillary light response as active vision.Curr. Dir. Psychol. Sci. 2015; 24: 374-378Crossref PubMed Scopus (88) Google Scholar,2Binda P. Murray S.O. Keeping a large-pupilled eye on high-level visual processing.Trends Cogn. Sci. 2015; 19: 1-3Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar]. Furthermore, the pupil diameter oscillates spontaneously at low frequencies, sometimes referred to as pupillary hippus [3Bouma H. Baghuis L.C.J. Hippus of the pupil: periods of slow oscillations of unknown origin.Vision Res. 1971; 11: 1345-1351Crossref PubMed Scopus (55) Google Scholar,4Wilhelm B. Wilhelm H. Lüdtke H. Streicher P. Adler M. Pupillographic assessment of sleepiness in sleep-deprived healthy subjects.Sleep. 1998; 21: 258-265PubMed Google Scholar]. Oscillation amplitude varies with many neural factors, including arousal and cortical excitability. Here we show that pupillary oscillations are modulated by mindfulness meditation, increasing by 53% compared to pre- and post-meditation baselines. The effect occurs only in trained meditators and is specific for low frequencies (below 1 Hz), with delta frequencies (1–5 Hz) unchanged. The study suggests that pupil size may be a useful marker of the altered cortical state during meditation.