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CHAPTER

15

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 nonrap-

id eye movement (NREM) and rapid eye movement (REM) sleep and the mecha-

nisms 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 pi-

neal 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 four-

neuron 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

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 approxi-

mately 24 h in length; that is, they are

circadian.

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-

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 dif-

fusely to wide regions of the neocortex and nuclei that project

to specific discrete portions of the neocortex and limbic sys-

tem. The nuclei that project to wide regions of the neocortex

are the

midline and intralaminar nuclei.

The nuclei that