test this was carried out by V. S. Ramachandran, a neuroscientist at
the University of California, San Diego. Touching an amputee’s face
(on the same side of the body as the amputated arm) elicits both the
feeling of the cheek being touched and the feeling of the phantom arm
being touched in specific locations (Fig. 16.5).
These reorganized perceptions also extend to temperature and
other sensations. Dripping warm or cold water down the amputee’s
cheek is experienced by the amputee as warm or cold water running
down the cheek and running down the phantom hand and arm. And I
once suggested to an amputee patient with whom I was working that
he might relieve a bothersome itch he was experiencing in his phan-
tom arm by scratching his cheek—it worked.
The somatosensory body map first discovered by Penfield is imme-
diately posterior to the central sulcus in the parietal lobe. Moving
immediately anterior to the central sulcus into the frontal lobe, we
encounter another body map also discovered by Penfield in his neu-
rosurgical explorations. This is a body map of neurons that send out
signals that initiate the contraction of skeletal muscles, involved in
the movements of our body. This region is called the primary motor
cortex, or M1. When neurons in M1 fire, signals propagate via the
spinal cord and eventually arrive at synapses with muscles of the
body, the neuromuscular junctions. At these junctions, acetylcholine
is released, which triggers contraction of muscle fibers.
As with the sensory areas of the cortex, there is contralateral
connection between M1 and the body, such that the right posterior
frontal lobe’s M1 controls movement of the left side of the body, and
the left posterior frontal lobe’s M1 controls movement of the right
side of the body. Lesions in M1 produce an inability to move muscles
associated with the corresponding part of the body map—that is,