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The Hindbrain

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The Hindbrain
The Central Nervous System: Making Sense of the World
61
■ What evidence would help to evaluate the alternatives?
As technology continues to be refined, the quality of fMRI scans will continue to
improve, giving us ever better images of where brain activity is taking place. But the
value of this scanning technology will depend on a better understanding of what it can
and cannot tell us about how brain activity is related to behavior and mental processes.
We also need more evidence about correlation and causation in fMRI research. For
example, a recent study conducted fMRI scans on compulsive gamblers as they played
a simple guessing game (Reuter et al., 2005). When they won the game, these people
showed an unusually small amount of activity in a brain area that is normally activated
by the experience of rewards, or pleasure. Noting the correlation between compulsive
gambling and lower-than-normal activity in the reward area, the researchers suggested
that an abnormality in the brain’s reward mechanisms might be responsible for gambling addiction. But recent case studies also suggest that compulsive gambling appears
in people taking a prescription drug that increases activity in reward areas—and that
the gambling stops when the drug is discontinued (Dodd et al., 2005). As noted in the
chapter on introducing psychology, correlation does not guarantee causation. Is the
brain activity reflected in fMRI scans causing the thoughts and feelings that take place
during the scanning process? Possibly, but those thoughts and feelings might themselves
be caused by activity elsewhere in the brain that affects the areas being scanned.
Reaching an understanding about questions like these will require continuing debate
and dialogue between those who dismiss fMRI and those who sing its praises. To make
this interaction easier, a group of government agencies and private foundations has
recently funded an fMRI Data Center (http://www.fmridc.org/f/fmridc). This facility
stores information from fMRI experiments and makes it available to both critics and
supporters of fMRI, who can review the research data, conduct their own analyses, and
offer their own interpretations. Having access to an ever-growing database such as this
will no doubt help scientists get the most out of fMRI technology while also helping
each other to avoid either overstating or underestimating the meaning of fMRI research.
■ What conclusions are most reasonable?
When the EEG was invented nearly 100 years ago, scientists had their first glimpse of
brain cell activity, as reflected in the “brain waves” traced on a long sheet of paper
rolling from the EEG machine (see Figure 4.3). To many of these scientists, EEG must
have seemed a golden gateway to an understanding of the brain and its relationship to
behavior and mental processes. EEG has, in fact, helped to advance knowledge of the
brain, but it certainly didn’t solve all of its mysteries. When all is said and done, the
same will probably be true of fMRI. It is an exciting new tool, and it offers previously
undreamed-of images of the structure and functioning of the brain, but it is unlikely
on its own to explain just how the brain creates our behavior and mental processes. It
seems reasonable to conclude, then, that those who question the use of fMRI to study
psychological processes are right in calling for a careful analysis of the value of this
important high-tech tool.
Although the meaning of fMRI data will remain a subject for debate, there is no
doubt that brain scanning techniques in general have opened new frontiers for biological psychology, neuroscience, and medicine (Goldstein & Volkow, 2002; Miller, 2003).
Let’s now explore some of the structures highlighted by these techniques, starting with
three major subdivisions of the brain: the hindbrain, the midbrain, and the forebrain.
The Hindbrain
hindbrain The portion of the brain
that lies just inside the skull and is a
continuation of the spinal cord.
Figure 2.8 shows the major structures of the brain. The hindbrain lies just inside the
skull and is actually a continuation of the spinal cord. Incoming signals from the spinal
cord first reach the hindbrain. Many vital autonomic functions, such as heart rate,
62
FIGURE
Chapter 2 Biology and Behavior
2.8
Brain
Major Structures of the Brain
This side view of a section cut down the
middle of the brain reveals the forebrain,
midbrain, hindbrain, and spinal cord. Many
of these subdivisions do not have clear-cut
borders, because they are all interconnected by fiber tracts. The brain’s anatomy
reflects its evolution over millions of
years. Newer structures (such as the cerebral cortex, which is the outer surface of
the forebrain) that handle higher mental
functions were built on older ones (such as
the medulla) that coordinate heart rate,
breathing, and other more basic functions.
Forebrain
Midbrain
Hindbrain
Reticular
formation
Cerebellum
Medulla
Spinal cord
medulla The area of the hindbrain
that controls vital autonomic functions
such as heart rate, blood pressure, and
breathing.
reticular formation A collection of
cells and fibers in the hindbrain and
midbrain that are involved in arousal
and attention.
cerebellum The part of the hindbrain
that controls finely coordinated
movements.
blood pressure, and breathing, are controlled by nuclei in the hindbrain, particularly
in an area called the medulla (pronounced “meh-DU-lah”).
Weaving throughout the hindbrain and into the midbrain is a mesh-like collection
of cells called the reticular formation (reticular means “net-like”). This network is
involved in arousal and attention. Cutting off fibers of the reticular system from the
rest of the brain would put a person into a permanent coma. Some of the fibers that
carry pain signals from the spinal cord connect in the reticular formation and immediately arouse the brain from sleep. Within seconds, the hindbrain causes your heart
rate and blood pressure to increase. You are awake and aroused.
The cerebellum (pronounced “sair-a-BELL-um”) is also part of the hindbrain. For a
long time its primary function was thought to be control of finely coordinated movements, such as threading a needle. We now know that the cerebellum also allows the eyes
to track a moving target accurately (Krauzlis & Lisberger, 1991) and that it may be the
storehouse for well-rehearsed movements, such as those associated with dancing, playing
a musical instrument, and athletics (McCormick & Thompson, 1984). The cerebellum
might also be involved in the learning of these skills (Hazeltine & Ivry, 2002), as well as
in more uniquely human tasks such as language and abstract thinking (Bower & Parsons,
2003). For instance, abnormalities in the cerebellum have been associated with reading
disabilities (Rae et al., 2002), and surgery that affects the cerebellum sometimes results in
a syndrome called cerebellar mutism, in which patients become unable to speak for periods ranging from a few days to several years (Gelabert-Gonzalez & Fernandez-Villa,
2001). In short, the cerebellum seems to be involved in both physical and cognitive agility.
Reflexes and feedback systems are important in the hindbrain. For example, if blood
pressure drops, heart action reflexively increases to make up for that decrease. If you
stand up quickly, your blood pressure can drop so suddenly that you feel lightheaded
until the hindbrain reflexively “catches up.” You will faint if the hindbrain does not activate the autonomic nervous system to increase your blood pressure.
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