Episodic timing: how spontaneous alpha clocks, retrospectively

We seldom time life events intently yet recalling the duration of events is lifelike. Is episodic time the outcome of a rational after-thought or of physiological clocks keeping track of time without our conscious awareness of it? To answer this, we recorded human brain activity with magnetoencephalography (MEG) during quiet wakefulness. Unbeknownst to participants, we asked them after the MEG recording to guess its duration. In the absence of overt attention to time, the relative amount of time participants’ alpha brain rhythms (α ~10 Hz) were in bursting mode predicted participants’ retrospective duration estimate. This relation was absent when participants prospectively measured elapsed time during the MEG recording. We conclude that α bursts embody discrete states of awareness for episodic timing. One-Sentence Summary In the human brain, the relative number of alpha oscillatory bursts at ~10 Hz can tell time when the observer does not attend to it.