Consciousness, the Brain, and Behavior
247
It is generally accepted that long-term memory forma-
tion involves processes that alter gene expression and result in
the synthesis of new proteins. This is achieved by a cascade
of second messengers that activate genes in the cell’s DNA.
These new proteins may be involved in the increased num-
ber of synapses that have been demonstrated after long-term
memory formation. They may also be involved in structural
changes in individual synapses (e.g., by an increase in the num-
ber of receptors on the postsynaptic membrane). This ability
of neural tissue to change because of activation is known as
plasticity.
Additional Facts Concerning Learning
and Memory
Certain types of learning depend not only on factors such as
attention, motivation, and various neurotransmitters, but also
on certain hormones. For example, the hormones epineph-
rine, ACTH, and vasopressin affect the retention of learned
experiences. These hormones are normally released in stress-
ful or even mildly stimulating experiences, suggesting that the
hormonal consequences of our experiences affect our memo-
ries of them.
Two of the opioid peptides, enkephalin and endorphin,
interfere with learning and memory, particularly when the
lesson involves a painful stimulus. They may inhibit learn-
ing simply because they decrease the emotional (fear, anxi-
ety) component of the painful experience associated with the
learning situation, thereby decreasing the motivation neces-
sary for learning to occur.
Memories can be encoded very rapidly, sometimes after
just one trial, and they can be retained over extended periods.
Information can be retrieved from memory stores after long
periods of disuse, and the common notion that memory, like
muscle, atrophies with lack of use is not always true. Also, unlike
working memory, memory storage apparently has an unlimited
capacity because people’s memories never seem so full that they
cannot learn something new. Although we have mentioned
specifi c areas of the brain that are active in learning, we want to
stress that memory traces are laid down in specifi c neural sys-
tems throughout the brain, and different types of memory tasks
utilize different systems. In even a simple memory task, such as
trying to recall a certain word from a previously seen word list,
different specifi c parts of the brain are activated in sequence. It
is as though several small “processors” are linked together in a
memory system for specifi c memory tasks.
Table 8–5
summarizes some general principles about
learning and memory.
Cerebral Dominance and Language
The two cerebral hemispheres appear to be nearly symmetri-
cal, but each has anatomical, chemical, and functional special-
izations. We have already mentioned that the left hemisphere
deals with the somatosensory (Chapter 7) and motor (Chapter
10) functions of the right side of the body, and vice versa. In
addition, in 90 percent of the population the left hemisphere
is specialized to produce language—the conceptualization of
what one wants to say or write, the neural control of the act
of speaking or writing, and recent verbal memory. This is even
true of the sign language some deaf people use.
Language is a complex code that includes the acts of lis-
tening, seeing, reading, and speaking. The major centers for
language function are in the left hemisphere in the temporal,
parietal, and frontal cortex next to the
sylvian fi
ssure,
which
separates the temporal lobe from the frontal and parietal lobes
(
Figure 8–15
). Each of the various regions deals with a sepa-
rate aspect of language. For example, distinct areas are spe-
cialized for hearing, seeing, speaking, and generating words
(
Figure 8–16
). There are even distinct brain networks for
different categories of things, such as “animals” and “tools.”
The cerebellum is important in speaking and writing, which
involve coordinated muscle contractions. Males and females
typically use different brain areas for language processing,
probably refl ecting different strategies (
Figure 8–17
).
Much of our knowledge about how language is produced
has been obtained from patients who have suffered brain dam-
age and, as a result, have one or more defects in language,
known as
aphasias
.
For example, in most people, damage to
the left cerebral hemisphere, but not to the right, interferes
with the capacity for language manipulation, and damage to
different areas of the left cerebral hemisphere affects language
use differently.
Damage to the temporal region known as
Wernicke’s
area
(see Figure 8–15) generally results in aphasias that are
more closely related to
comprehension
—the individuals have dif-
fi culty understanding spoken or written language even though
their hearing and vision are unimpaired. Although they may
have fl uent speech, their speech is incomprehensible. In con-
trast, damage to
Broca’s area,
the language area in the fron-
tal cortex responsible for the articulation of speech, can cause
expressive
aphasias—the individuals have diffi culty carrying out
the coordinated respiratory and oral movements necessary for
Table 8–5
General Principles of Learning
and Memory
1. There are multiple memory systems in the brain.
2. Working memory requires changes in existing neural
circuits, whereas long-term memory requires new protein
synthesis and growth.
3. These changes may involve multiple cellular mechanisms
within single neurons.
4. Second-messenger systems appear to play a role in mediating
cellular changes.
5. Changes in the properties of membrane channels are often
correlated with learning and memory.
Adapted from John M. Beggs et al. “Learning and Memory: Basic Mechanisms,” in Michael
J. Zigmond, Floyd E. Bloom, Story C. Landis, James L. Roberts, and Larry R. Squire, eds.,
Fundamental Neuroscience,
Academic Press, San Diego, CA, 1999.
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