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stimulating parts of this region in the left or right hemisphere caused movements of specific
body parts on the opposite side of the body. Fritsch and Hitzig had discovered what is now
TEACH 1.4-7 called the motor cortex.
Teaching Tip Mapping the Motor Cortex Luckily for brain surgeons and their patients, the brain has
no sensory receptors. Knowing this, in the 1930s, Otfrid Foerster and Wilder Penfield were
Walk through Figure 1.4-13 with your able to map the motor cortex in hundreds of wide-awake patients by stimulating different
students. It features the sensory cortical areas and observing the body’s responses. They discovered that body areas requiring
homunculus, the visual picture of precise control, such as the fingers and mouth, occupy the greatest amount of cortical space
(Figure 1.4-13). In one of his many demonstrations of motor behavior mechanics, Spanish
how much space in the motor and neuroscientist José Delgado stimulated a spot on a patient’s left motor cortex, triggering the
somatosensory cortexes each part of right hand to make a fist. Asked to keep the fingers open during the next stimulation, the
the body takes up. These diagrams patient, whose fingers closed despite his best efforts, remarked, “I guess, Doctor, that your
electricity is stronger than my will” (Delgado, 1969, p. 114).
show dramatically how much cortex
is devoted to complex areas of the
body such as the face and hands and Elbow Arm Shoulder Torso Hip Hip Torso Neck Arm Head
how little is devoted to rather simple Hand Wrist Knee Knee Elbow Forearm Hand Fingers
areas such as the leg and elbow. The Fingers Ankle Leg
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
amount of space occupied on the Thumb Foot Thumb
Toes
homunculus is directly related to each Brow Toes Genitals Eye Nose
Neck
Eye Face
area’s sensitivity.
Output: Motor cortex Input: Somatosensory cortex
Face
(Right hemisphere section (Left hemisphere section receives Lips
controls the body’s left side) input from the body’s right side)
Lips
TEACH 1.4-7 Jaw
Enrichment Jaw
Share the following information with Tongue Pharynx Tongue
your students. Wilder Penfield, a Swallowing abdominal Science Source/Macmillan
Intra-
famous neurosurgeon, along with his
colleague Herbert Jasper, perfected
a technique to treat epilepsy through FIGURE 1.4-13
surgery by selectively lesioning cells Motor cortex and somatosensory cortex tissue devoted to each body part
in the brain that triggered the seizures. As you can see from this classic though inexact representation, the amount of cortex devoted to a body part in the motor cortex (in the frontal lobes)
or in the somatosensory cortex (in the parietal lobes) is not proportional to that body part’s size. Rather, the brain devotes more tissue to sensitive
By keeping patients conscious on the Copyright © Bedford, Freeman & Worth Publishers.
areas and to areas requiring precise control. So, your fingers have a greater representation in the cortex than does your upper arm.
operating table, Penfield was able to
stimulate cells in the brain and map
Scientists can now predict a monkey’s arm motion just before it moves — by repeatedly
areas before destroying the offending measuring motor cortex activity preceding specific arm movements (Livi et al., 2019). Such
cells. The sensory homunculus, which is findings have opened the door to research on brain-controlled computer technology.
depicted in Figure 1.4-13, was largely Brain–Machine Interfaces Researchers wondered: By stimulating the brain, could we en-
created by Penfield through his map- motor cortex a cerebral cortex able a person with paralysis to move a robotic limb? Could a brain–machine interface help
area at the rear of the frontal
ping surgeries to treat epilepsy. It has lobes that controls voluntary someone with paralysis learn to command a cursor to write an email? To find out, researchers
been essentially unaltered since its movements. implanted 100 tiny recording electrodes in the motor cortexes of three monkeys (Nicolelis,
2011; Serruya et al., 2002). As the monkeys gained rewards by using a joystick to follow a
creation in the 1950s.
72 Unit 1 Biological Bases of Behavior

ENGAGE 1.4-7
(5 minutes) To demonstrate how guess. Greater accuracy for touch to the hand 15/12/23 9:23 AM
03_myersAPpsychology4e_28116_ch01_002_163.indd 72
areas of greater sensitivity are will be obvious. The difference in sensitivity
assigned greater areas of the somato- is explained by the fact that far more cortex
sensory cortex, ask for a volunteer to is devoted to the hand than to the back. (Ask
come to the front of the room. Have students to look at Figure 1.4-13 again).
the volunteer close their eyes and
report the number of fingers you press Information from Motiff, J. P. (1987). Physiological
on their skin. Randomly press one to psychology: The sensory homunculus. In V. P. Makosky,
four digits lightly on their back and L. G. Whittemore, & A. M. Rogers (Eds.), Activities handbook
for the teaching of psychology (Vol. 2, pp. 51–52). American
on the hand. Inform the class of the Psychological Association.
correct number after the volunteer’s

72 Unit 1 Biological Bases of Behavior

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