An illustration of a typical correlation of eyeball movements with brain-state changes.

<p>Top: diagrams showing the pupil centre movements in the nasal-temporal and dorsal-ventral directions, separately for the left (upper diagram) and right (lower diagram) eyes from the example in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062430#pone-0062430-g006" target="_blank">Figure 6</a>. Bottom: two diagrams showing cyclic alternations of the brain state. The black diagram shows row ECoG signal, and the colour surface plot below indicates the dominant frequency in ECoG signal. The hottest (red) and coldest (blue) colours represent the highest and lowest values in the power spectrum at the particular frequency calculated for the window sliding over the raw ECoG signal (step 10 s; width 300 s). Activation phase, indicated by shaded area, is characterised by dominant theta frequency (≈4 Hz) in ECoG signal, and deactivation phase is characterised by dominant delta frequency (≈1 Hz) in ECoG. Note that the relocation of the pupil from the temporal to nasal position, concomitant with the transition from ECoG deactivation to activation, is markedly faster than the gradual shift of the pupil centre from the nasal to temporal position.