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

42

THE PHYSICAL BRAIN

Monitoring the Brain 43

MEG

In addition to making electrical activity, the brain produces a faint

magnetic field. This is detected by a magnetoencephalography

(MEG) machine and can be used to create a real-time account

of activity in the cerebral cortex. MEG is limited by the weakness

of the brain’s magnetism, but the technique can detect rapid

fluctuations in brain activity, which take place over a few

thousandths of a second, better than other monitoring systems.

This form of cognitive therapy uses an EEG to create a feedback loop

between a person’s mental state and their brain activity. This makes

it easier for people to learn ways to control unwanted mental activity,

such as anxiety.

NEUROFEEDBACK

Magnetic field

around nerve pulse

Cerebral

cortex

SQUID array in

form of skull cap

EEG charts

electrical activity

in the brain.

Game gives

reward when the

required brain state

is registered (for

example, low

anxiety).

Computer

turns neural

patterns into

a dynamic display,

such as an

interactive

game.

With practice,

the brain acquires

the habit of being in

the rewarded state.

1

3

4 2

Functional MRI and

diffusion tensor imaging

MRI (see pp.40–41) can be extended

to collect information about what

the brain is doing. Functional MRI

(fMRI) scanning tracks the flow of

blood through the brain, specifically

showing where it is giving oxygen

to neurons and thus indicating

which regions are active in real

time. Subjects are asked to carry out

mental and physical tasks while

monitored by fMRI to create a

The Adult Brain and Teenagers

spinal cord that combines anatomy

with activity levels. Diffuse tensor

imaging (DTI) also uses MRI but

tracks the natural movement of

water through brain cells. It is used

to build up a map of the white-

matter connections within the brain.

Area of increased

activity

Area of reduced

activity

Interpreting an fMRI image

An fMRI scan begins with establishing a

baseline of activity in the brain. The scan

then shows up regions that fluctuate from

this baseline, allowing researchers to figure

out which areas are excited or inhibited

during particular tasks.

How MEG works

MEG uses sensitive

detectors called

superconducting

quantum interference

devices (SQUIDS) to

pick up fleeting

magnetic fields made

by the electrical

pulses of neurons.

Direction of

nerve pulse

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