Default-mode network
A coordinated set of brain regions — medial prefrontal cortex, posterior cingulate, hippocampus — most active during internally-directed thought: remembering, imagining, mind-wandering.
The network was named because early neuroimaging studies found it active during rest and quiet during externally-focused tasks — the brain’s "default" mode. Later work showed it is not idling at all; it is doing autobiographical memory, mental time travel, future planning, and self-referential thinking. It is the circuitry behind the inner life.
In SDAM the default-mode network activates less strongly and in a less coordinated way during autobiographical recall. This is one of the fMRI findings from the Palombo 2015 paper and has been replicated since. The network is the likely seat of the re-experiencing layer that SDAM selectively diminishes, leaving the semantic scaffolding intact.