Ganong's Review of Medical Physiology, 23rd Edition

Electrical Activity of the
Brain, Sleep–Wake States,
& Circadian Rhythms
OBJECTIVES
After studying this chapter, you should be able to:
■ Describe the primary types of rhythms that make up the electroencephalogram
(EEG).
■ List the main clinical uses of the EEG.
■ Summarize the behavioral and EEG characteristics of each of the stages of nonrapid
eye movement (NREM) and rapid eye movement (REM) sleep and the mechanisms
responsible for their production.
■ Describe the pattern of normal nighttime sleep in adults and the variations in this
pattern from birth to old age.
■ Discuss the circadian rhythm and the role of the suprachiasmatic nuclei (SCN) in its
regulation.
■ Describe the diurnal regulation of synthesis of melatonin from serotonin in the pineal
gland and its secretion into the bloodstream.
INTRODUCTION
Most of the various sensory pathways described in Chapters
11–14 relay impulses from sense organs via three- and fourneuron
chains to particular loci in the cerebral cortex. The
impulses are responsible for perception and localization of
individual sensations. However, they must be processed in the
awake brain to be perceived. At least in mammals, there is a
spectrum of behavioral states ranging from deep sleep through
light sleep, REM sleep, and the two awake states: relaxed
awareness and awareness with concentrated attention. Discrete
THALAMUS, CEREBRAL CORTEX,
& RETICULAR FORMATION
THALAMIC NUCLEI
The thalamus is a large collection of neuronal groups within
the diencephalons; it participates in sensory, motor, and lim-
C H A P T E R
15
patterns of brain electrical activity correlate with each of these
states. Feedback oscillations within the cerebral cortex and
between the thalamus and the cortex serve as producers of this
activity and possible determinants of the behavioral state.
Arousal can be produced by sensory stimulation and by
impulses ascending in the reticular core of the midbrain. Many
of these activities have rhythmic fluctuations that are approximately
24 h in length; that is, they are circadian.
bic functions. Virtually all information that reaches the cortex
is processed by the thalamus, leading to its being called the
“gateway” to the cerebral cortex.
The thalamus can be divided into nuclei that project diffusely
to wide regions of the neocortex and nuclei that project
to specific discrete portions of the neocortex and limbic system.
The nuclei that project to wide regions of the neocortex
are the midline and intralaminar nuclei. The nuclei that
229