Neural correlates of temporality: default mode variability and temporal awareness

The continual background awareness of duration is an essential structure of consciousness, conferring temporal extension to the many objects of awareness within the evanescent sensory present. Seeking the possible neural correlates of ubiquitous temporal awareness, this article reexamines fMRI data from off-task "default mode" (DM) periods in 25 healthy subjects studied by Grady et al. ("Age-related Changes in Brain Activity across the Adult Lifespan,"Journal of Cognitive Neuroscience 18(2), 2005). "Brain reading" using support vector machines detected information specifying elapsed time, and further analysis specified distributed networks encoding implicit time. These networks fluctuate; none are continuously active during DM. However, the aggregate regions of greatest variability closely resemble the default mode network. It appears that the default mode network has an important role as a state-dependent monitor of temporality.