BODY & BRAIN
be bad for brains
Mice deprived of social lives
have shrunken neurons
BY LAURA SANDERS
Mice yanked out of their community and
held in solitary isolation show signs of
After a month of being alone, the mice
had smaller nerve cells in certain parts of
the brain. Other brain changes followed,
scientists reported at a news briefing
It’s not yet known whether similar
damage happens in the brains of isolated
humans. If so, the results have implications for the health of people who spend
much of their time alone, including the
estimated tens of thousands of inmates
in solitary confinement in the United
States and elderly people in institutionalized care facilities.
The new results, along with other
recent brain studies, clearly show that
for social species, isolation is damaging,
says neurobiologist Huda Akil of the
University of Michigan in Ann Arbor.
“There is no question that this is changing the basic architecture of the brain.”
Neurobiologist Richard Smeyne
of Thomas Jefferson University in
Philadelphia and colleagues raised communities of multiple generations of mice
in large enclosures packed with toys,
mazes and things to climb. When some
of the animals reached adulthood, they
were taken out and put individually into
“a typical shoebox cage,” Smeyne said.
This abrupt switch induced changes in
the brain, Smeyne and colleagues found.
The overall size of nerve cells, or neurons, shrank by about 20 percent after
a month of isolation. That shrinkage
held roughly steady over three months
as mice remained in isolation.
To the researchers’ surprise, after a
month of isolation, the mice’s neurons
had a higher density of spines — struc-
tures for making neural connections — on
message-receiving dendrites. An increase
in spines usually signals something posi-
tive. “It’s almost as though the brain is
trying to save itself,” Smeyne said.
But by three months, the density of
dendritic spines had dropped back to
baseline levels, perhaps a sign that the
brain couldn’t save itself when faced
with continued isolation. “It’s tried to
recover, it can’t, and we start to see these
problems,” Smeyne said.
The scientists uncovered other worri-
some signals, including reductions in a
protein called BDNF, which spurs neu-
ral growth. Levels of the stress hormone
cortisol changed, too. Compared with
mice in groups, isolated mice also had
more broken DNA in their neurons.
The researchers studied neurons in
the sensory cortex, a brain area involved
in taking in information, and the motor
cortex, which helps control movement.
It’s not yet known whether similar effects
happen in other brain areas, Smeyne said.
It’s also not known how the neural
changes relate to mice’s behavior. In
people, long-term isolation can lead
to depression, anxiety and psychosis.
Brainpower is affected, too. Isolated
people develop problems reasoning,
remembering and navigating.
Smeyne is doing longer-term studies
aimed at figuring out the effects of neuron
shrinkage on thinking skills and behavior.
He and colleagues plan to return isolated
mice to their groups to see if the brain
changes can be reversed. Those types of
studies get at an important issue, Akil
says. “When is it too far gone?” s
Lack of sleep can induce anxiety
A sleepless night can leave the brain spinning with anxiety the next day. In
healthy adults, overnight sleep deprivation triggered anxiety the next morning,
along with altered brain activity patterns, scientists reported November 5.
People with anxiety disorders often have trouble sleeping. The new results
uncover the reverse effect — that poor sleep can lead to anxiety. “The sleep
loss makes the anxiety worse, which in turn makes it harder to sleep,” says sleep
researcher Clifford Saper of Harvard Medical School.
Sleep researchers Eti Ben Simon and Matthew Walker of the University of
California, Berkeley studied the anxiety levels of 18 people. Following either a
night of sleep or a night of staying awake, participants took anxiety tests. After
sleep deprivation, these people’s anxiety levels were 30 percent higher than
when they had slept. On average, anxiety scores reached levels seen in people
with anxiety disorders, Ben Simon said in a news briefing.
What’s more, sleep-deprived people’s brain activity changed. In response
to emotional videos, brain areas involved in emotions were more active, and
the prefrontal cortex, an area that can put the brakes on anxiety, was less
active, functional MRI scans showed. — Laura Sanders
Pot may change decision-making parts of teen boys’ brains
Marijuana use during the teenage years may change the brain in key decision-making areas, a study in rats suggests.
Behavioral neuroscientist Eliza Jacobs-Brichford of the University of Illinois at
Chicago and colleagues gave adolescent male and female rats a marijuana-like
compound. Afterward, the team found changes in parts of the brain involved in
making decisions. Normally, many of the nerve cells there are surrounded by
sturdy webs that help stabilize connections between nerve cells. But in males
that had been exposed to the compound, fewer of these nerve cells, which help
put the brakes on other cells’ activity, were covered by nets. Drug exposure
didn’t seem to affect females’ nets. “Males look more susceptible to these
drugs,” Jacobs-Brichford said November 7. — Laura Sanders