2019-10-19_New_Scientist

16 | New Scientist | 19 October 2019

YOUR brain looks different if you

have depression. But many of the

differences seem to be caused by

depression, rather than precede it.

When neuroscientists compare

the brains of people with and

without depression, there are

common dissimilarities. For

example, people with depression

tend to have a smaller

hippocampus, a brain region

important in forming memories.

But it has been difficult to work

out whether such differences

cause the symptoms of depression

or result from the disorder, says

Heather Whalley at the University

of Edinburgh, UK.

To answer the question, she and

her colleagues turned to two huge

genetic databases. Consumer

genetic testing company 23andMe

holds information on the DNA and

depressive symptoms of tens of

thousands of individuals, and the

UK Biobank collects DNA, lifestyle

and behaviour questionnaires and

brain scans from thousands more.

They used this, as well as earlier

research, to create a polygenic risk

score (PRS) for depression. A PRS

assigns weight to various genetic

factors thought to contribute to

the risk of a condition. They made

sure the PRS worked by testing it

in a separate group of 11,214 people.

The team then assessed the

brain scans and behaviour records

of people with a PRS that put them

at risk of depression. People with

higher genetic risk tended to have

less white matter in their brains,

and it didn’t seem to function as

well. White matter is the tissue

that makes up most of our brains.

Whalley and her colleagues

then analysed how closely both

brain structure and symptoms of

depression were related to genetic

factors. Genes are present from

birth, so if genetic factors are

more closely linked to symptoms,

for example, that suggests the

symptoms were present before

the brain structure differences.

They found that many brain

differences appear to be caused

by depression. There was one

exception: differences in a brain

structure called the anterior

thalamic radiation appear to

come before depression (bioRxiv,

doi.org/dcmk). This suggests the

genes that puts a person at risk of

depression do so via this structure.

Whalley’s team also found that a

combination of childhood trauma

and poverty leaves individuals at

greatest risk of depression.

Behaviours linked to depression

could end up impacting the brain’s

white matter connections more

generally, says Maxime Taquet at

the University of Oxford. “It might

be that patients with depression...

do not use some of the brain

connections that other people

would use,” he says.

Being socially withdrawn, or

focusing more on the negative

than the positive, could have an

effect, he says. “We know that if we

don’t use a pathway in the brain,

that pathway starts to shrink.” ❚

“ It might be that people

with depression don’t use

some brain connections

other people would use”

Genetics

ZEPHYR/SCIENCE PHOTO LIBRARY

News

White matter tissue

is found throughout

our brains

Environment

US green economy

jobs eclipse those in

fossil fuel industry

THE green economy has grown

so much in the US that it employs

around 10 times as many people

as the fossil fuel industry – despite

the past decade’s oil and gas boom.

The fossil fuel sector, from

coal mines to gas power plants,

employed around 900,000 people

in the US in 2015-16, government

figures show. But Lucien Georgeson

and Mark Maslin at University

College London found that over

the same period this was vastly

outweighed by the green economy,

which provided nearly 9.5 million

jobs, or 4 per cent of the working

age population. The pair defined the

green economy broadly, covering

everything from renewable energy

to environmental consultancy.

Their analysis showed the green

economy is worth $1.3 trillion,

or about 7 per cent of US GDP

(Palgrave Communications, DOI:

10.1057/s41599-019-0329-3).

The figures don’t cover the

presidency of Donald Trump, who

promised to protect coal mining

jobs and exploit oil and gas

resources. But Maslin says the

figures show that Trump’s policy

is economically misguided.

“The Trump administration

with the ‘America first’ approach

of ‘fossil fuels are good’, is stupid

when it comes to economics.

If you want to be a hard-nosed

neoliberal economist you would say,

‘Let’s support the green economy

as much as possible.’”

The US stopped recording green

job statistics several years ago, but

these suggested 3.4 million people

worked in the sector in 2011.

Maslin and Georgeson used a

much broader set of 26 sub-sectors

including wind and solar power,

marine pollution controls, carbon

capture, biodiversity and air

pollution. Maslin says the figures

have been underestimated in the

past, partly because the green

economy is so diffuse. ❚

Adam Vaughan

Green economy

jobs include

everything from

installing solar

panels to

environmental

consultancy

DEREK MEIJER/ALAMY STOCK PHOTO

Jessica Hamzelou

Depression alters brain structure

Many differences seem to be the result of the condition rather than its cause