How the Brain Works The Facts Visually Explained by DK (z-lib.org)

60

THE PHYSICAL BRAIN

Nature and Nurture 61

Epigenetic changes

Changes in the way genes are used (or expressed)

that occur during a person’s lifetime are called

epigenetic changes. They affect gene function,

rather than gene structure, and can be passed on

to a person’s children, although they may last for only

a few generations. In the brain, they can influence

functions such as learning, memory, reward-seeking,

and response to stress. There are two main forms:

methylation, in which a compound joins on to the DNA;

and histone modification, which alters how tightly the

DNA is coiled.

DNA methylation

In this process, a molecule of a methyl

compound attaches to one of the bases in

a gene’s DNA sequence. The effect is to stop

or restrict the activity of that gene.

NON-ADOPTED TWIN

BIOLOGICAL PARENTS ADOPTIVE PARENTS

ADOPTED TWIN

Base pairs in most of

sequence unchanged

Methyl compound

Chronic emotional (^) attached to DNA base
stress in children can impair
development of the amygdala,
hippocampus, and frontal lobes,
leading to problems with memory,
emotion, and learning. It restricts the
action of genes regulating the
growth of networks of neurons.
However, moderate “positive”
stress (fun) can aid
learning.
Studies on children have
found that growing up poor or
deprived can impair the
development of areas related to
memory, language processing,
decision-making, and self-control.
However, a safe, happy home,
with interesting things to do,
seems to reduce the harm.
Loneliness has been
found to alter the production of
neurotransmitters, so people
perceive less reward from social
contact and are more likely to
misinterpret others’ attitudes as
threatening. However, maintaining
close social ties can support
memory and cognitive skills.
A healthy diet (see pp.54–55)
rich in omega-3 fatty acids, B
vitamins, and antioxidants keeps
blood vessels healthy, improving
blood flow to the brain. These
nutrients have also been linked to
improving memory and
maintaining cognitive
functions in older people.

STRE

SS L

EV

EL

S

PHYS

ICA

L (^) S
UR
RO
U
N
D
IN
G
S

HC

R

O

M

O

SO

M

ES

SO

CIA

L (^) N
ET
W
O
R
K
S

DIE

T

NURT

NATURE URE

Studies of twins reveal how much of a specific trait, such

as intelligence quotient (IQ), is due to inheritance and

how much is due to environment. Most twins grow up

in the same home; however, identical twins share 100

percent of their genes, while nonidentical (fraternal)

twins share only 50 percent. If a trait is more evident

in identical twins than in fraternal ones, or appears in

identical twins who were separated at birth, it suggests

that genetics has a stronger influence than environment.

STUDYING TWINS

US_060-061_Nature_and_Nurture.indd 61 20/09/2019 12:33