Biology Reference
In-Depth Information
thinking and problem solving. In keeping with their extraordinary cog-
nitive abilities, humans have larger and more convoluted cerebral cor-
tices than the other primates. Nevertheless, the basic organization of
the entire cerebrum, including its arrangement of the major parts of the
brain (lobes and the fissures that separate them), is similar in monkeys,
apes, and people (figure 2).
How, exactly, the human brain works is becoming better under-
stood because of medical imaging instruments that permit researchers
to identify parts of the brain that become activated when individuals
experience specific thoughts or sensations (for example, machines that
use functional magnetic resonance imaging [f [fMRI] or positron emis-
sion tomography [PET]). From such studies, it is clear that thinking
is a highly dynamic affair that involves multiple areas of the cerebral
cortex
—no matter how simple the particular thought or action is. In
other words, one usually cannot point to a particular convolution and
say that this bump contributes exclusively to such-and-such an activity.
Although this might appear to be bad news for endocast enthusiasts,
expansions of parts of the cerebral cortex can, nevertheless, be informa-
tive, because, as shown in figure 2, certain regions are, broadly speaking,
associated with functions such as seeing, hearing, experiencing sensa-
tions from different parts of the body, moving those parts, planning
what to do next, understanding and producing speech (in humans), and
so on.
Primates and other mammals share an overall similarity in the gen-
eral organization of their brains, including cortical representations of
sensory and motor functions of the body in appropriate anatomical
sequences (i.e., similar to the schematic in figure 2). Significantly, if a
particular part of a species' anatomy is especially important for its life-
style, the amount of cerebral cortex representing that part of the body
is likely to be enlarged. In dramatic incidences, this sometimes happens
to such an extent that localized expansions, or even new sulci, occur on
digits of raccoons' forepaws are greatly enlarged on their brains and are
