HUMANS & SOCIE TY
Shifts from drought to floods
ruined water infrastructure
BODY & BRAIN
How your brain is like a film editor
Hippocampus partitions events to store them as memories
BY BRUCE BOWER
At the medieval city of Angkor, flooding
after decades of scant rainfall triggered
a devastating breakdown of the largest
water system in the preindustrial world,
new evidence suggests.
Intense monsoon rains bracketed by
decades of drought set off a chain reaction
of failures in Angkor’s interconnected
water network, in what’s now Cambodia,
computer simulations show. The climate-induced crumbling of the system
hastened the city’s demise, scientists
conclude October 17 in Science Advances.
“Angkor’s critical [water] infrastructure acted to accelerate the impact of
climatic disruption,” says geoscientist
Dan Penny of the University of Sydney.
Penny and colleagues devised a model
of how a rapid shift to periods of intense
BY LAURA SANDERS
The brain’s hippocampus may be the
film editor of our lives, slicing continuous experiences into discrete cuts that
can be stored as memories. That’s the
idea raised by a study that analyzed
brain scan data from people watching
the movie Forrest Gump.
“Research like this helps us identify
‘ What is an event?’ from the point of view
of the brain,” says memory psychologist
Gabriel Radvansky of the University of
Notre Dame in Indiana.
Many lab tests of memory involve taking in discrete, dull lists of information.
“So much research is done with these
little bits and pieces — words, pictures,
things like that,” Radvansky says. But
those dry tidbits aren’t what the human
Medieval Angkor (Angkor Wat temple shown)
suffered a big blow when the city’s water
system reacted badly to a fluctuating climate,
computer simulations suggest.
rainfall affected Angkor’s water system at
the peak of its complexity in the 1300s. A
series of simulations indicate that, above
a critical volume of water flow, earthen
channels carrying water into the system
began to erode and widen. Water was
then unevenly shunted through junctions
in the network, gushing into some connected channels and trickling into others.
Meanwhile, accumulating sediment
further decreased the volume of water
that newly parched channels could
carry, intensifying the uneven flow of
water through the system. A breakdown
of the entire water network — used for
irrigation, drinking water and flood control — would soon have followed.
By the 1200s, Angkor was the world’s
most extensive city, covering about
1,000 square kilometers (SN: 5/14/16,
p. 22). The city had spent the previous several hundred years building and
expanding a network of canals, embankments, reservoirs, moats and other
structures devoted to water management.
In the 1400s, Angkor’s king and many
commoners mysteriously abandoned the
city. Some scientists have attributed the
brain usually handles. “The mind is built
to deal with complex events.”
As a closer approximation to real life,
researchers studied functional MRI data
from 15 people who watched Forrest
Gump and 253 people who watched Alfred
Hitchcock’s TV drama Bang! You’re Dead.
A separate group of 16 observers watched
each of the productions and pressed buttons to indicate when they thought one
event ended and another began.
With the data in hand, cognitive neuro-
scientists Aya Ben-Yakov and Rik Henson
of the University of Cambridge aligned
participants’ brain activity with the tran-
sition points marked by the observers. A
brain structure called the hippocampus,
important for memory and navigation,
seemed particularly active at these junc-
city’s demise to war with neighbors and
possibly the tumultuous replacement of
Hinduism with Buddhism in the region.
But the new study paints a convincing
picture of climate-induced infrastructure
collapse, says archaeologist Charles
Higham of the University of Otago in
Dunedin, New Zealand. Angkor, for
example, depended on irrigation for rice
fields. A breakdown of the water system
would have undermined not only harvests but also weakened public beliefs
that the king held supernatural powers
justifying his rule, Higham suspects. s
tures, the team reports online October 8
in the Journal of Neuroscience. The brain
structure was most active when the
observers had indicated a shift from one
event to another.
These transitions didn’t always involve
jumps to ne w places or times in the story.
One such boundary came near the beginning of Forrest Gump as Forrest sits
quietly on a bench. Suddenly, he blurts
out his famous greeting: “Hello. My
name’s Forrest. Forrest Gump.” The
hippocampus may have helped slice that
continuous bench scene into two events:
before talking and after talking. Such divisions may help package information into
discrete pieces that can then be stored as
memories, the researchers suspect.
Of course, films only approximate
firsthand experiences, Ben-Yakov says.
It’s not clear how the hippocampus
behaves when people are personally
involved in events. “Our goal is to understand real life,” she says. s