5 Steps to a 5 AP Psychology 2019

States of Consciousness ❮ 117

changes as we age. Electroencephalograms (EEGs) can be recorded with electrodes on
the surface of the skull. EEGs have revealed that brain waves change in form systematically
throughout the sleep cycle (see Figure 9.1). When you are awake, your EEG shows beta
waves when you are alert and alpha waves when you are relaxed. As you fall asleep, you pass
into a semiwakeful state of dreamlike awareness, known as the hypnagogic state; you feel
relaxed, fail to respond to outside stimuli, and begin the first stage of sleep, Non-REM-1
EEGs of NREM-1 sleep show theta waves, which are higher in amplitude and lower in
frequency than alpha waves. As you pass into NREM-2, your EEG shows high-frequency
bursts of brain activity (called sleep spindles) and K complexes. As you fall more deeply
asleep, your NREM-3 sleep EEG shows very high amplitude and very low-frequency delta
waves. In this stage EEGs show mostly delta waves. Your heart rate, respiration, tempera-
ture, and blood flow to your brain are reduced. You secrete growth hormone involved
in maintaining your physiological functions. Non-REM-3 was originally split into two

Figure 9.1 (a) Electroencephalograms of human

sleep stages. (b) Sleep stages during a typical night.

Awake

Hours of sleep

EE

G sleep stage

s 1

1234567

2

REM REM REM REM

3

4

(b)

(a)

Awake

Stage 1

NREM

Alpha

EE

G

Stage 2

NREM

Theta

(sleep spindles;

K-complexes)

Stage 3 and 4

NREM

Delta

REM

246810 12

Time (seconds)

14 16 18 20