The Brain and Behavior 53
ing with those areas of the cortex which are essential for nor-
mal body function. Thus electrical stimulation of the cortex
has a practical relevance for the treatment of the patient un-
dergoing surgery. For the neurosurgeon the value of the re-
sults of this stimulation for establishing neurophysiological
generalizations is secondary. Nevertheless, over the years
Penfield and his colleagues have collected sufficient data
from cortical mappings to be able to describe certain char-
acteristics of the surface of the cortex in considerable detail.
The actual stimulation procedure is comparatively simple
once the surface of the brain has been exposed. An electrode
providing a brief current (a fraction of a millisecond) at
voltages from K to 5 volts is touched to some point on the sur-
face of the right hemisphere of the cortex. Tire patient, who
is conscious throughout the operation, may report a tingling
sensation on the upper portion of the left leg, flex the left
hand, or perhaps contract the left leg. The location of each
response is marked with a numbered ticket; a secretary
records the numbers and the responses, and the total surface
area with tickets affixed is photographed. After the excision
of the pathological tissue, further stimulation may be carried
out. Then the incision is closed. (Cf. Penfield & Rasmussen,
1950, pp. 4-9.)
As indicated above, the cortical diagrams Penfield and his
associates prepared using all the apparatus available to mod-
ern neurosurgery were in substantial agreement with the dia-
grams prepared from studies of animals before 1900. But in
the course of their work and the work of other neurophysiol-
ogists it became more and more difficult to understand the
function performed by the sensory and motor projection
areas in the mediation of environment and behavior. These
difficulties arose in the course of investigations designed for