Summary
1-1 The Brain in the Twenty-First Century
Studying the brain and behavior leads us to better understand our
origins, our human nature, the causes of many behavioral
disorders, and the rationale behind treatment for disorders.
The human nervous system is composed of the CNS, which
includes the brain and the spinal cord, and the PNS, through
which the brain and spinal cord communicate with sensory
receptors, with muscles and other tissues, and with the internal
organs. The cerebrum and the cerebellum have undergone the
most growth in large-brained animal species.
We define behavior as any kind of movement, including
mental processes such as thinking and imagining. In animals,
behavior is caused by nervous system activity. Behavioral
flexibility and complexity vary greatly across species, as does
the nervous system.
For some species, including humans, the brain is the organ
that exerts control over behavior. The brain seems to need
ongoing sensory and motor stimulation to maintain its intelligent
activity.
1-2 Perspectives on Brain and Behavior
171
,Mentalism views behavior as a product of an intangible entity
called the mind (psyche); the brain has little importance.
Dualism is the notion that the immaterial mind acts through the
material brain to produce language and rational behavior,
whereas the brain alone is responsible for the “lower” actions
that we have in common with other animal species.
Materialism, the view that brain function fully accounts for all
behavior—language and reasoning included—guides
contemporary research on the brain and behavior. Support for the
materialistic view comes from the study of natural selection—the
evolutionary theory that behaviors such as human language
evolved from the simpler language abilities of human ancestors
—and from discoveries about how genes function. Experiments
follow the process of science: (1) formulate a theory, (2) generate
a question (hypothesis), (3) design a procedure to test it, and (4)
evaluate the results to confirm or modify the theory.
After severe TBI, the brain demonstrates a remarkable ability
to recover, but after either mild or severe injury, a person can be
left with a permanent disability that prevents full recovery to
former levels of function. Brain imaging techniques can confirm
severe disabilities such as MCS, locked-in syndrome, and PVS.
1-3 Evolution of Brains and of Behavior
Behavioral neuroscientists subscribe to the evolutionary
principle that all living organisms are descended from a common
ancestor. Brain cells and muscles are quite recent developments
172
,in the evolution of life on Earth. Because they evolved only
once, a similar basic pattern exists in the nervous systems of all
animals.
The nervous systems of some animal lineages have become
more complex, with evolution featuring first a nerve net,
followed by a bilaterally symmetrical and segmented nervous
system, a nervous system controlled by ganglia, and eventually,
in chordates, a nervous system featuring a brain and spinal cord.
Mammals are a class of chordates characterized by a large
brain relative to body size. Modern humans belong to the primate
order, which is distinguished by especially large brains, and to
the family of great apes, whose members’ limber shoulders allow
them to brachiate (hang and swing by the arms).
1-4 Evolution of the Human Brain and Behavior
One of our early hominid ancestors was probably an
Australopithecus, who lived in Africa several million years ago.
It is from an australopith species that Homo evolved through
species such as Homo habilis and Homo erectus. Modern
humans, Homo sapiens sapiens, appeared about 200,000 years
ago.
Since Australopithecus, the hominid brain has increased in
size almost threefold, as has its number of brain cells. The
increases were associated with area (topography) and connection
(connectome) changes. The EQ describes brain size relative to
173
, body size, but a complete comparison of different species’ brains
requires brain cell counts. Among the factors hypothesized to
have stimulated brain evolution in human species are
environmental challenges and opportunities, such as climate
changes that favored the natural selection of adaptability and
more complex behavior patterns. Brain and behavior changes in
hominids were mediated by perhaps only a few genes that
appeared de novo in hominids. Also proposed are lifestyle
changes such as social cooperation and cooking food, changes in
physiology, and changed maturation rate.
1-5 Modern Human Brain Size and Intelligence
Evolutionary principles learned from studying the brain and
behavior across species do not easily apply to the brain and
behavior within a single species, such as Homo sapiens. People
vary widely in body size, brain size, and, likely, the number of
brain cells and the connections between brain cells. Any of these
factors can contribute to varying kinds of intelligence, making a
simple comparison of brain size and general intelligence unwise.
Recognizing the great extent to which modern human
behavior, rather than being inherent in our nervous systems,
results from cultural learning and transmission is paramount to
understanding how our brains function. Memes may spread from
person to person and culture to culture.
174
1-1 The Brain in the Twenty-First Century
Studying the brain and behavior leads us to better understand our
origins, our human nature, the causes of many behavioral
disorders, and the rationale behind treatment for disorders.
The human nervous system is composed of the CNS, which
includes the brain and the spinal cord, and the PNS, through
which the brain and spinal cord communicate with sensory
receptors, with muscles and other tissues, and with the internal
organs. The cerebrum and the cerebellum have undergone the
most growth in large-brained animal species.
We define behavior as any kind of movement, including
mental processes such as thinking and imagining. In animals,
behavior is caused by nervous system activity. Behavioral
flexibility and complexity vary greatly across species, as does
the nervous system.
For some species, including humans, the brain is the organ
that exerts control over behavior. The brain seems to need
ongoing sensory and motor stimulation to maintain its intelligent
activity.
1-2 Perspectives on Brain and Behavior
171
,Mentalism views behavior as a product of an intangible entity
called the mind (psyche); the brain has little importance.
Dualism is the notion that the immaterial mind acts through the
material brain to produce language and rational behavior,
whereas the brain alone is responsible for the “lower” actions
that we have in common with other animal species.
Materialism, the view that brain function fully accounts for all
behavior—language and reasoning included—guides
contemporary research on the brain and behavior. Support for the
materialistic view comes from the study of natural selection—the
evolutionary theory that behaviors such as human language
evolved from the simpler language abilities of human ancestors
—and from discoveries about how genes function. Experiments
follow the process of science: (1) formulate a theory, (2) generate
a question (hypothesis), (3) design a procedure to test it, and (4)
evaluate the results to confirm or modify the theory.
After severe TBI, the brain demonstrates a remarkable ability
to recover, but after either mild or severe injury, a person can be
left with a permanent disability that prevents full recovery to
former levels of function. Brain imaging techniques can confirm
severe disabilities such as MCS, locked-in syndrome, and PVS.
1-3 Evolution of Brains and of Behavior
Behavioral neuroscientists subscribe to the evolutionary
principle that all living organisms are descended from a common
ancestor. Brain cells and muscles are quite recent developments
172
,in the evolution of life on Earth. Because they evolved only
once, a similar basic pattern exists in the nervous systems of all
animals.
The nervous systems of some animal lineages have become
more complex, with evolution featuring first a nerve net,
followed by a bilaterally symmetrical and segmented nervous
system, a nervous system controlled by ganglia, and eventually,
in chordates, a nervous system featuring a brain and spinal cord.
Mammals are a class of chordates characterized by a large
brain relative to body size. Modern humans belong to the primate
order, which is distinguished by especially large brains, and to
the family of great apes, whose members’ limber shoulders allow
them to brachiate (hang and swing by the arms).
1-4 Evolution of the Human Brain and Behavior
One of our early hominid ancestors was probably an
Australopithecus, who lived in Africa several million years ago.
It is from an australopith species that Homo evolved through
species such as Homo habilis and Homo erectus. Modern
humans, Homo sapiens sapiens, appeared about 200,000 years
ago.
Since Australopithecus, the hominid brain has increased in
size almost threefold, as has its number of brain cells. The
increases were associated with area (topography) and connection
(connectome) changes. The EQ describes brain size relative to
173
, body size, but a complete comparison of different species’ brains
requires brain cell counts. Among the factors hypothesized to
have stimulated brain evolution in human species are
environmental challenges and opportunities, such as climate
changes that favored the natural selection of adaptability and
more complex behavior patterns. Brain and behavior changes in
hominids were mediated by perhaps only a few genes that
appeared de novo in hominids. Also proposed are lifestyle
changes such as social cooperation and cooking food, changes in
physiology, and changed maturation rate.
1-5 Modern Human Brain Size and Intelligence
Evolutionary principles learned from studying the brain and
behavior across species do not easily apply to the brain and
behavior within a single species, such as Homo sapiens. People
vary widely in body size, brain size, and, likely, the number of
brain cells and the connections between brain cells. Any of these
factors can contribute to varying kinds of intelligence, making a
simple comparison of brain size and general intelligence unwise.
Recognizing the great extent to which modern human
behavior, rather than being inherent in our nervous systems,
results from cultural learning and transmission is paramount to
understanding how our brains function. Memes may spread from
person to person and culture to culture.
174
