436
UNIT 3
Regulation and Integration of the Body
12
balance (the position of the head in space) is located in the
posterior part of the insula and adjacent parietal cortex.
6.
Olfactory cortex.
Te
primary olfactory (smell) cortex
lies
on the medial aspect of the temporal lobe in a small region
called the
piriform lobe
which is dominated by the hooklike
uncus
(Figure 12.6b). Afferent fibers from smell receptors in
the superior nasal cavities send impulses along the olfactory
tracts that are ultimately relayed to the olfactory cortices. Te
outcome is conscious awareness of different odors.
Te olfactory cortex is part of the primitive
rhinen-
cephalon
(ri
0
nen-sef
9
ah-lon; “nose brain”), which in-
cludes all parts of the cerebrum that receive olfactory
signals—the orbitofrontal cortex, uncus, and associated
regions located on or in the medial aspects of the tem-
poral lobes, and the protruding olfactory tracts and bulbs
that extend to the nose. During the course of evolution,
most of the “old” rhinencephalon has taken on new func-
tions concerned chiefly with emotions and memory. It has
become part of the “newer” emotional brain, called the
limbic system
, which we will consider later in this chapter.
Te only portions of the human rhinencephalon still de-
voted to smell are the olfactory bulbs and tracts (described
in Chapter 13) and the greatly reduced olfactory cortices.
7.
Gustatory cortex.
Te
gustatory (taste) cortex
(gus
9
tah-tor-
e), a region involved in perceiving taste stimuli, is located in
the insula just deep to the temporal lobe (Figure 12.6a).
8.
Visceral sensory area.
Te cortex of the insula just pos-
terior to the gustatory cortex is involved in conscious
perception of visceral sensations. Tese include upset
stomach, full bladder, and the feeling that your lungs will
burst when you hold your breath too long.
Homeostatic Imbalance
12.2
Damage to the
primary visual cortex
(Figure 12.6) results in
functional blindness. By contrast, individuals with a damaged
visual association area can see, but they do not comprehend
what they are looking at.
Multimodal Association Areas
Te association areas that we have
considered so far (colored light red or light blue in Figure 12.6)
have all been tightly tied to one kind of primary motor or sensory
cortex (colored dark red or dark blue). Most of the cortex, though,
consists of complexly connected
multimodal association areas
(colored light violet in Figure 12.6) that receive inputs from multi-
ple senses and send outputs to multiple areas.
In general, information flows from sensory receptors to the
appropriate primary sensory cortex, then to a sensory associa-
tion cortex and then on to the multimodal association cortex.
Multimodal association cortex allows us to give meaning to the
information that we receive, store it in memory, tie it to previ-
ous experience and knowledge, and decide what action to take.
Tose decisions are relayed to the premotor cortex, which in
turn communicates with the motor cortex. Te multimodal as-
sociation cortex seems to be where sensations, thoughts, and
emotions become conscious. It is what makes us who we are.
Suppose, for example, you drop a bottle of acid in the chem lab
and it splashes on you. You see the bottle shatter, hear the crash,
feel your skin burning, and smell the acid fumes. Tese individual
As with the primary motor cortex, the body is repre-
sented spatially and upside down according to the site of
stimulus input, and the right hemisphere receives input
from the le± side of the body. Te amount of sensory cor-
tex devoted to a particular body region is related to that re-
gion’s sensitivity (that is, to how many receptors it has), not
its size. In humans, the face (especially the lips) and fin-
gertips are the most sensitive body areas, so these regions
are the largest parts of the
somatosensory homunculus
(shown in the right half of Figure 12.7).
2.
Somatosensory association cortex.
Te
somatosensory
association cortex
lies just posterior to the primary so-
matosensory cortex and has many connections with it.
Te major function of this area is to integrate sensory in-
puts (temperature, pressure, and so forth) relayed to it via
the primary somatosensory cortex to produce an under-
standing of an object being felt: its size, texture, and the
relationship of its parts.
For example, when you reach into your pocket, your so-
matosensory association cortex draws upon stored memo-
ries of past sensory experiences to perceive the objects you
feel as coins or keys. Someone with damage to this area
could not recognize these objects without looking at them.
3.
Visual areas.
Te
primary visual (striate) cortex
is seen on
the extreme posterior tip of the occipital lobe, but most of it
is buried deep in the
calcarine sulcus
in the medial aspect of
the occipital lobe (Figure 12.6b). Te largest cortical sensory
area, the primary visual cortex receives visual information
that originates on the retina of the eye. Tere is a contralat-
eral map of visual space on the primary visual cortex, analo-
gous to the body map on the somatosensory cortex.
Te
visual association area
surrounds the primary
visual cortex and covers much of the occipital lobe. Com-
municating with the primary visual cortex, the visual as-
sociation area uses past visual experiences to interpret
visual stimuli (color, form, and movement), enabling us to
recognize a flower or a person’s face and to appreciate what
we are seeing. We do our “seeing” with these cortical neu-
rons. However, complex visual processing involves the en-
tire posterior half of the cerebral hemispheres. Particularly
important are two visual “streams”—one running along
the top of the brain and handling spatial relationships and
object location, the other taking the lower road and focus-
ing on recognizing faces, words, and objects.
4.
Auditory areas.
Each
primary auditory cortex
is located
in the superior margin of the temporal lobe abutting the
lateral sulcus. Sound energy exciting the hearing recep-
tors of the inner ear causes impulses to be transmitted to
the primary auditory cortex, where they are interpreted as
pitch, loudness, and location.
Te more posterior
auditory association area
then
permits the perception of the sound stimulus, which we
“hear” as speech, a scream, music, thunder, noise, and so
on. Memories of sounds heard in the past appear to be
stored here for reference. Wernicke’s area, which we de-
scribe later, includes parts of the auditory cortex.
5.
Vestibular (equilibrium) cortex.
Imaging studies show that
the part of the cortex responsible for conscious awareness of
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