Arousal reframed as an organism‑wide dynamic system

The temporal evolution of a hidden, low-dimensional and organism-wide process, inferred from measuring the pupil of an eye, has been shown to account for complex spatio-temporal patterns of brain activity over timescales of seconds. This points to an underlying dynamic that continuously structures the unfolding of brain, body and behavioural variables. Pupil size can predict complex brain dynamics, suggesting that both reflect an organism-wide dynamic process.