The Economist - UK (2022-04-09)

72 Science & technology The Economist April 9th 2022

thiswaywouldalsoincreaseenergysecu­

rity.Andeveryfractionofa degreeshaved

offfuturewarmingreducesclimaterisks,

evenif the1.5°Ctargetismissed.

The covid­19 pandemic presented an

opportunitytousetheresultingeconomic

turmoiltostimulategreengrowth.There­

sponseofgovernmentswaspatchyatbest.

Today,astheWestcomestogripswitha

deepeningenergycrisis,itfacesa similar

challenge,butwithaddedurgencyinlight

ofthelatest climatewarnings fromthe

ipcc’s scientists.n

Neuroscience

Frames of mind

I

fadoctorwantstoknowhowwella

child is growing, she can turn to clinical­

ly  validated  charts  that  lay  out  precisely

how  that  child  compares  to  the  norm  for

their age and sex. Not only can the doctor

look up, say, how many centimetres shor­

ter or taller the child is than the average for

their  age,  but  exactly  what  height  percen­

tile  they  fall  into.  Medical  diagnoses  can

then  be  made  based  on  an  absolute  com­

parison with the statistical norm.

Reference charts are an important tool

in  modern  primary  medicine,  covering

many  aspects  of  a  person’s  healthy  devel­

opment.  There  is,  however,  a  big  gap  in

their  coverage:  the  human  brain.  Richard

Bethlehem and Simon White from the Uni­

versity  of  Cambridge  and  Jakob  Seidlitz

from the University of Pennsylvania want

to fix that. Writing in Nature, the neurosci­

entists  describe  the  most  comprehensive

effort  yet  to  create  a  standard  against

which  someone’s  brain  development  can

be measured through their lifetime.

Their brain charts were compiled from

more  than  120,000  three­dimensional

brain  scans  belonging  to  more  than

100,000  patients  who  took  part  in  more

than 100 different research studies. The da­

ta  set  included  people  of  all  ages,  ranging

from babies still developing in the womb,

just  over  100  days  after  conception,  to

adults more than 100 years old.

With  that  data,  the  scientists  cata­

logued  how  the  average  human  brain

evolved  from  cradle  to  grave,  focusing  on

three  types  of  brain  tissue:  grey  matter

(made  up  of  neuron  cell  bodies),  white

matter (the filaments connecting neurons)

and  tissue  conveying  cerebrospinal  fluid

(the  brain’s  plumbing  system).  The  scien­

tists  paid  particular  attention  to  the  cere­

bral  cortex,  the  outermost  layer  of  the

brain,  responsible  for  higher­order  brain

functions.  They  observed  grey  matter  in

the cortex peaking in volume at 5.9 years, 2

to 3 years later than previously thought.

Having  characterised  the  development

and ageing of the average human brain, the

scientists  modelled  the  distribution

around  it,  charting  the  percentile­by­per­

centile variation in the structure of human

brain tissue. This allowed them to investi­

gate  how  the  brains  of  patients  with  va­

rious  developmental  or  degenerative  dis­

orders  compare  to  more  typical  brains.

“Our  investigation  confirmed  that  Alz­

heimer’s  disease,  mild  cognitive  impair­

ment and schizophrenia show marked re­

structuring  of  brain  tissue  relative  to  a

more  typical  brain  of  the  same  age  and

sex,” says Dr Seidlitz.

The catalogue turned up some surpris­

es  too.  Autism,  for  example,  is  generally

thought to present differently in male and

female  patients,  but  there  is  little  sign  of

that difference in their brain tissue. In con­

trast, attention deficit hyperactivity disor­

der  (adhd)—which  presents  similarly  by

sex—displays  the  largest  average  differ­

ence in brain structure between male and

female patients of any diagnosis they ana­

lysed.  Over  the  course  of  a  lifetime,  the

brains of male adhdpatients appear to be

skewed towards below­average volumes of

grey  matter,  white  matter  and  cerebrospi­

nal  fluid.  The  brains  of  female  adhdpa­

tients,  on  the  other  hand,  were  ever­so­

slightly skewed towards higher volumes of

the same tissues. 

What  these  differences  in  brain  size

mean is not yet clear. And the authors cau­

tion that their brain charts are not yet rea­

dy for clinical use, not least because the da­

taset  they  used  has  several  limitations.

“Unfortunately,  the  data  we  compiled  re­

flect  the  demographic  biases  of  neurosci­

ence  research  in  general,  ie,  most  studies

are from Europe or North America, and ov­

er­represent  patients  of  European  ances­

try,” says Dr Bethlehem. 

To reflect the full diversity of normative

human  brain  development,  a  more  repre­

sentative  dataset  will  be  required.  Once

that  is  accomplished,  the  utility  of  brain

charts  can  begin  to  be  tested  in  a  clinical

setting.  One  day,  hopefully,  these  charts

could  become  a  useful  tool  in  tracking  a

person’s brain healthorspotting the earli­

est  physical  signs  ofbraindisorders  such

as Alzheimer’s disease.n

Reference charts for brain development

could be used to spot problems early

The shape of brains to come

Perception

A rose by any

other name

T

o the swedes,  there  are  few  odours

more  delectable  than  the  scent  of

surströmming, a type of fermented herring.

To  most  non­Swedes  there  are  probably

few  odours  more  repulsive—the  fish  has

been  described  variously  as  smelling  like

rancid  cat  litter,  vaguely  faecal  or  even

corpse­like.  In  determining  which  scents

people  find  pleasant  and  which  they  do

not,  surströmming suggests  culture  must

play a sizeable part. 

New  research,  however,  suggests  that

might not be the case. Artin Arshamian, a

neuroscientist  at  the  Karolinska  Institute

in Sweden, and Asifa Majid, a psychologist

at the University of Oxford, began with the

expectation that culture would play an im­

portant  role  in  determining  pleasant

smells. This was not just because of exam­

ples  like  that  of  fermented  herring.  They

People from different cultures like

(and dislike) the same scents

Mmm...cheesy