Page 529 - Fundamentals of anatomy physiology

516 Unit 3 Control and Regulation
Figure 14–17 Hemispheric Lateralization. Functional differences between the left and right cerebral hemispheres.

Left Cerebral Hemisphere Right Cerebral Hemisphere

LEFT HAND RIGHT HAND

Prefrontal Prefrontal
cortex cortex

Speech center Anterior commissure

14 Writing C
O
Auditory cortex R
(right ear) P
U
General interpretive center S Analysis by touch
(language and mathematical
C
calculation) A
L Auditory cortex
L (left ear)

O
S
U Spatial visualization
M and analysis

Visual cortex Visual cortex
(right visual field) (left visual field)

The brain contains billions of neurons, and their activity gen- who are either concentrating on a task, under stress, or in a state
erates an electrical field that can be measured by electrodes of psychological tension.
placed on the brain or on the outer surface of the skull. The
electrical activity changes constantly, as nuclei and cortical Theta waves may appear transiently during sleep in nor-
areas are stimulated or quiet down. A printed recording of mal adults but are most often observed in children and in
the electrical activity of the brain is called an electroence­ intensely frustrated adults. The presence of theta waves under
phalogram (EEG). The electrical patterns observed are called other circumstances may indicate the presence of a brain disor-
brain waves. der, such as a tumor.

Typical brain waves are shown in Figure 14–18a–d. Alpha Delta waves are very-large-amplitude, low-frequency
waves occur in the brains of healthy, awake adults who are rest- waves. They are normally seen during deep sleep in individuals
ing with their eyes closed. Alpha waves disappear during sleep, of all ages. Delta waves are also seen in the brains of infants
but they also vanish when the individual begins to concentrate (whose brains are still developing) and in awake adults when
on some specific task. a tumor, vascular blockage, or inflammation has damaged por-
tions of the brain.
During attention to stimuli or tasks, higher-frequency beta
waves replace alpha waves. Beta waves are typical of individuals Electrical activity in the two hemispheres is generally
synchronized by a “pacemaker” mechanism that appears to