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Chapter 8
changes in behavior that vary according to the part of the
brain affected, and can include seizures and a temporary loss
of consciousness.
The Waking State
Behaviorally, the waking state is far from homogeneous,
refl ecting the wide variety of things you might be doing at any
given moment. The most prominent EEG wave pattern of an
awake, relaxed adult whose eyes are closed is a slow oscillation
of 8 to 13 Hz known as the
alpha rhythm
(
Figure 8–3a
).
The alpha rhythm is recorded best over the parietal and occipi-
tal lobes and is associated with decreased levels of attention.
When alpha rhythms are generated, subjects commonly report
that they feel relaxed and happy. However, people who nor-
mally experience more alpha rhythm than usual have not been
shown to be psychologically different from those with less.
When people are attentive to an external stimulus or are
thinking hard about something, the alpha rhythm is replaced
by lower-amplitude, high-frequency (>13 Hz) oscillations, the
beta rhythm
(
Figure 8–3b
). This transformation, known as
the
EEG arousal,
is associated with the act of paying atten-
tion to a stimulus rather than with the act of perception itself.
For example, if people open their eyes in a completely dark
room and try to see, EEG arousal occurs even though they
perceive no visual input. With decreasing attention to repeated
stimuli, the EEG pattern reverts to the alpha rhythm.
Sleep
The EEG pattern changes profoundly in sleep. As a person
becomes increasingly drowsy, a decrease occurs in alpha-wave
amplitude and frequency. When sleep actually occurs, the
EEG shifts toward slower-frequency, higher-amplitude wave
patterns known as the
theta rhythm
(4–8 Hz) and the
delta
rhythm
(slower than 4 Hz) (
Figure 8–4
). Changes in pos-
ture, ease of arousal, threshold for sensory stimuli, and motor
output accompany these EEG changes.
There are two phases of sleep whose names depend
on whether or not the eyes move behind the closed eyelids:
NREM
(nonrapid eye movement) and
REM
(rapid eye move-
ment) sleep. The EEG waves during NREM sleep are of high
amplitude and slow frequency, so NREM sleep is also referred
to as slow-wave sleep. The initial phase of sleep—NREM
sleep—is itself divided into four stages. Each successive stage
is characterized by an EEG pattern with a slower frequency
and higher amplitude than the preceding one (
Figure 8–4a
).
Sleep begins with the progression from stage 1 to stage 4,
which normally takes 30 to 45 min. The process then reverses
itself; the EEG ultimately resuming the low-voltage, high-fre-
quency, asynchronous pattern characteristic of the alert, awake
state (
Figure 8–4b
). Instead of the person waking, however,
the behavioral characteristics of sleep continue at this time,
but this sleep also includes rapid eye movement (REM sleep).
REM sleep is also called
paradoxical sleep
because the
sleeper is diffi
cult to arouse despite having an EEG character-
istic of the alert, awake state. In fact, brain O
2
consumption is
higher during REM sleep than during the NREM or awake
states! When awakened during REM sleep, subjects gener-
ally report that they have been dreaming. This is true even in
people who generally do not remember dreaming when they
awaken on their own.
If uninterrupted, sleep continues in this cyclical fashion,
tending to move from stages 1, 2, and 3, to 4 then back up
from 4 to 3, 2, and 1, where NREM sleep is punctuated by an
episode of REM sleep. Continuous recordings of adults show
that the average total night’s sleep comprises four or fi ve such
Figure 8–4
The EEG record of a person (a) passing from the awake state to
deep sleep (stage 4) and (b) during REM sleep. The high-amplitude
waves of the late stages of slow-wave sleep (theta and delta rhythms)
demonstrate the synchronous activity pattern in cortical neurons.
The desynchronous pattern during REM sleep is similar to that
observed in awake individuals.
Time
(a)
Awake
(b)
REM (paradoxical) sleep
Stage 1
Stage 2
Stage 3
Stage 4
NREM (slow-wave) sleep
(a)
(b)
Alpha rhythm
(relaxed with eyes closed)
Beta rhythm
(alert)
Time
Figure 8–3
The (a) alpha and (b) beta rhythms shown on an EEG.
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