82 CHAPTER 2
THE CEREBRAL HEMISPHERES: ARE YOU IN YOUR RIGHT MIND?
2.14 Explain how some brain functions differ between the left and right
hemispheres.I’ve heard that some people are right brained and some are left
brained. Are the two sides of the brain really that different?Most people tend to think of the two cerebral hemispheres as identical twins. Both sides
have the same four lobes and are arranged in much the same way. But language seems
to be confined to only the left hemisphere in about 90 percent of the population (Toga &
Thompson, 2003). What other special tasks do the two halves of the cerebrum (the upper
part of the brain consisting of the two hemispheres and the structures connecting them)
engage in, and how do researchers know about such functions? Participate in the exper-
iment simulation Hemispheric Specialization to test the language abilities of the two hemi-
spheres Simulate the Experiment, Hemispheric Specialization.
SPLIT-BRAIN RESEARCH Roger Sperry was a pioneer in the field of hemisphere specializa-
tion. He won a Nobel Prize for his work in demonstrating that the left and right hemispheres
of the brain specialize in different activities and functions (Sperry, 1968). In looking for a way
to cure epilepsy (severe muscle spasms or seizures resulting from brain damage), Sperry cut
through the corpus callosum, the thick band of neural fibers that joins the two hemispheres.
In early research with animals, this technique worked and seemed to have no side effects.
The first people to have this procedure done also experienced relief from their severe epilep-
tic symptoms, but testing found that (in a sense) they now had two brains in one body.
The special testing involves sending messages to only one side of the brain, which is
now possible because the connecting tissue, the corpus callosum, has been cut. Remember
that each hemisphere is largely responsible for controlling, or receiving information from, the
opposite side of the body. Figure 2.16 shows what happens with a typical split-brain patient.spatial neglect
condition produced most often
by damage to the parietal lobe
association areas of the right
hemisphere, resulting in an inability
to recognize objects or body parts
in the left visual field.
cerebrum
the upper part of the brain consisting
of the two hemispheres and the struc-
tures that connect them.
everything in the left visual field. Damage to areas of the frontal and temporal lobes
may also play a part along with the parietal damage. Spatial neglect can affect the
left hemisphere, but this condition occurs less frequently and in a much milder form
than right-hemisphere neglect (Corbetta et al., 2005; Heilman et al., 1993; Springer &
Deutsch, 1998).
When the doctor examined this woman, he tried to get her to notice her left side by
holding up a mirror (remember, she was not blind—she just would not notice anything on
her left side unless her attention was specifically called to it). She responded correctly when
asked what the mirror was and she was able to describe her appearance correctly, but when
an assistant held a pen just within the woman’s reach, reflected in the mirror on her left side,
she tried to reach through the mirror to get the pen with her good right hand. When the doc-
tor told her that he wanted her to grab the real object and not the image of it in the mirror, she
told him that the pen was behind the mirror and even tried to reach around to get it.
Clearly, persons suffering from spatial neglect can no longer perceive the world in
the same way as other people do. For these people, the left sides of objects, bodies, and
spaces are somewhere “through the looking glass.”Questions for Further Discussion- If a person with spatial neglect only eats the food on the right side of the plate, what
could caregivers do to help that person get enough to eat? - What other odd things might a person with spatial neglect do that a person with
normal functioning would not? What other things might a person with spatial neglect
fail to do?