The Biological Perspective 69Instead, various neuroimaging techniques can do this, either by directly imaging the
brain’s structure (the different parts) or its function (how the parts work). These methods
also vary in their degree of spatial resolution (ability to see fine detail) and temporal res-
olution (ability to time lock a recorded event).
MAPPING STRUCTURE As hinted at earlier, aside from observing the person’s behav-
ior, scientists had to wait until a person died to fully investigate if there were changes
or damage to the individual ’s brain. Fortunately, modern neuroimaging allows us to
image the brain’s structure while the person is still alive.
COMPUTED TOMOGRAPHY (CT) Scientists have several ways to look inside the human
brain without causing harm to the person. One way is to take a series of X-rays of the brain,
aided by a computer. This is accomplished during a CT scan (computed tomography
involves mapping “slices” of the brain by computer). CT scans can show stroke damage,
tumors, injuries, and abnormal brain structure. (See Figure 2.10a.) A CT scan is also the
structural imaging method of choice when there is metal in the body (e.g., a bullet or sur-
gical clips) and useful for imaging possible skull fractures. (See Figure 2.10b.)
MAGNETIC RESONANCE IMAGING (MRI) As useful as a CT scan can be for imaging the
skull, it doesn’t show very small details within the brain. The relatively newer technique
of magnetic resonance imaging, or MRI, provides much more detail (see Figure 2.10c
and Figure 2.10d), even allowing doctors to see the effects of very small strokes. The
person getting an MRI scan is placed inside a machine that generates a powerful mag-
netic field to align hydrogen atoms in the brain tissues (these normally spin in a random
fashion); then radio pulses are used to make the atoms spin at a particular frequency
and direction. The time it takes for the atoms to return to their normal spin allows a
computer to create a three-dimensional image of the brain and display “slices” of that
image on a screen.
Using MRI as a basis, several techniques have been developed that allow us to study
other aspects of the brain. MRI spectroscopy allows researchers to estimate the concentra-
tion of specific chemicals and neurotransmitters in the brain. Another fascinating tech-
nique is called DTI, or diffusion tensor imaging. The brain has two distinct color regions,
gray matter, the outer areas consisting largely of neurons with unmyelinated axons, and
white matter, the fiber tracts consisting of myelinated axons (the myelin is responsible for
the lighter color). DTI uses MRI technology to provide a way to measure connectivity in
the brain by imaging these white matter tracts. DTI has been used to investigate normal
computed tomography (CT) scan
brain-imaging method using comput-
er-controlled X-rays of the brain.
magnetic resonance imaging (MRI)
brain-imaging method using radio
waves and magnetic fields of the body
to produce detailed images of the brain.Figure 2.10 Mapping Brain Structure
Fig 2.10a: CT scan from a 5-year-old girl with a head injury and skull fracture, depicting the brain and swelling associated with the injury. Fig 2.10b: Same CT
scan highlighting the skull fracture (indicated by the red arrow). Contrast the brain detail of Fig 2.10a with the MRI scan in Fig 2.10c (different, adult individual).
Note the scans are in the horizontal plane, separating the brain into upper and lower portions. Fig 2.10d: Different type of MRI image from an older adult, with
cortical cell loss (atrophy) and white matter changes. Notice the enlarged ventricles and widening of the grooves (sulci) in the outer cortex as compared to
2.10c. Figs 2.10a, b, c, and d images created with OsiriX software; CT and MRI data courtesy of N. White.
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