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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
called the motor cortex.

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
able to map the motor cortex in hundreds of wide-awake patients by stimulating different
cortical areas and observing the body’s responses. They discovered that body areas requiring
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
neuroscientist José Delgado stimulated a spot on a patient’s left motor cortex, triggering the
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
right hand to make a fist. Asked to keep the fingers open during the next stimulation, the
patient, whose fingers closed despite his best efforts, remarked, “I guess, Doctor, that your
electricity is stronger than my will” (Delgado, 1969, p. 114).

Copyright © Bedford, Freeman & Worth Publishers.

Hip Torso Neck Arm Head Elbow Forearm Hand
Hip
Torso
Arm
Shoulder
Wrist
Elbow
Hand
Knee Knee Fingers
Leg
Fingers
Ankle
Foot Thumb
Toes Eye
Thumb
Toes Nose
Neck
Genitals
Brow
Eye Face
Face
Output: Motor cortex Input: Somatosensory cortex
(Right hemisphere section (Left hemisphere section receives Lips
controls the body’s left side) input from the body’s right side)
Lips
Jaw
Jaw
Tongue Intra- Pharynx
Tongue
Swallowing abdominal Science Source/Macmillan

FIGURE 1.4-13
Motor cortex and somatosensory cortex tissue devoted to each body part
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
areas and to areas requiring precise control. So, your fingers have a greater representation in the cortex than does your upper arm.

Scientists can now predict a monkey’s arm motion just before it moves — by repeatedly
measuring motor cortex activity preceding specific arm movements (Livi et al., 2019). Such
findings have opened the door to research on brain-controlled computer technology.
Brain–Machine Interfaces Researchers wondered: By stimulating the brain, could we en-
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
lobes that controls voluntary someone with paralysis learn to command a cursor to write an email? To find out, researchers
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

72 Unit 1 Biological Bases of Behavior

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