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

THE PHYSICAL BRAIN

Monitoring the Brain

Monitoring the Brain

Being able to collect information from a living brain

at work has revolutionized both our understanding

of how the brain functions and brain medicine.

EEG

The simplest brain monitor is the electroencephalograph (EEG). It uses

electrodes positioned all over the cranium to pick up an electrical field

created by the activity of neurons in the cerebral cortex. The varying

levels may be displayed as waves (“ordinary EEG”) or colored areas

(quantitative EEG, or QEEG). EEG can reveal evidence of seizure disorders,

such as epilepsy, and signs of injury, inflammation, and tumors. The

painless procedure is also used to assess brain activity in coma patients.

Electrodes held close

to skull by cap

Wire carries signal

to an amplifier

Low-frequency waves

are widely spaced

High-frequency waves are

packed tightly together

WHY DOES

THE BRAIN PRODUCE

ELECTROMAGNETIC FIELDS?

Neurons use pulses of electric

charge to transmit messages.

The activity of billions of

cells accumulates into

a constant field.

These rhythms are associated with

learning and complex problem-

solving tasks. They may originate

from the binding together of

groups of neurons into

networks.

Originating from both hemispheres

at the front of the brain, beta

waves are associated with

physical activity and with

states of concentration

and anxiety.

These typically originate from the

back of the brain and are usually

stronger in the dominant

hemisphere. They are seen

during both relaxed

and alert states.

These waves are typically seen

during some stages of sleep but

also when a person is

engaged in complex

problem-solving

tasks.

Usually seen in young children,

theta waves are also evident

during states of relaxation,

creativity, and

meditation.

MORE THAN

32 HZ

Time

Amplitude

14 –32 HZ

Time

Amplitude

8 –14 HZ

Time

Amplitude

4–8 HZ

Time

Amplitude

0.1– 4 HZ

Time

Amplitude

Types of EEG wave

Neighboring cells in the cortex fire in

synchrony, creating wavelike changes in the

intensity of the electrical field. Characteristic

wave patterns (named after letters of the

Greek alphabet) have been found to be

closely associated with certain brain states.

GA

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W

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LT

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