YOUR BRAINperson was requested to do. By contrast, attending to an external task,
no matter what it involved, appeared to put this same network to sleep.
Raichle’s team dubbed this the “default mode network”. In an interview
for The Psychologist magazine Raichle recalled being troubled by the fact
that “even if you just had somebody lying in the scanner with their eyes
open or closed and they weren’t doing anything other than being awake
and then you asked them to do something demanding, not only did the
areas that you might expect light up, but areas went down – that was the
opening for us.”
What do we know about what the default network is actually for? One
theory is that the network comes alive when we’re mind-wandering,
thinking about the past and possible futures. The psychologist Malia
Mason and colleagues tested this idea directly with a study published in
- They invited participants into a brain scanner and asked them to
perform either novel or highly practised memory tasks. Earlier on they’d
established that the participants’ minds were, as you’d expect, more likely
to wander during the highly practised tasks, which had become rather
boring. The key finding was that the default mode network was signifi-
cantly more active during the practised tasks compared with the novel
tasks. What’s more, this was particularly the case among the participants
who reported being more prone to mind-wandering.
The brain asleep
If mind-wandering is what the brain does on stand-by then you might
think that sleep is what happens when the brain is fully shut down. On
the contrary, ground-breaking research in the 1950s showed that the
brain is highly active during sleep as it completes a series of ninety-
minute cycles drifting back and forth between deep, slow-wave sleep and
rapid eye-movement, or “REM”, sleep. If you were to record the surface
electrical activity of a person’s brain while they enjoyed forty winks of
REM sleep, you’d not see much difference from the kind of activity their
brain displays while it’s awake. Today, a continuous stream of new find-
ings is uncovering just how important this sleepy activity is to memory
consolidation, filtering and creativity.
An important study of rats, published in the 1990s, showed that sleep
reactivates patterns of brain cell firing that occur during wakefulness,
thus consolidating the memories represented in those patterns. Matthew
Wilson and Bruce McNaughton, then at the University of Arizona,
recorded the brain activity of rats performing a spatial task that involved