UNIT 3 - Biological Bases of Behavior
3B: The Brain
Outline:
1. The Tools of Discovery: Having Our Heads Examined
 Recording the brain's electrical activity
 Neuroimaging techniques
2. Older Brain Structures
 The Brainstem
 The Thalamus
 The Cerebellum
 The Limbic System
3. The Cerebral Cortex
 Structure of the Cortex
 Functions of the Cortex
 Language
 The Brain's Plasticity
4. Our Divided Brain
 Splitting the Brain
5. The Brain and Consciousness
 Cognitive Neuroscience
 Dual Processing
 The Two-Track Mind
1
Scientists have developed tools to study the connection between the brain and our
behavior and perception. One of them is a technique called lesion which means to destroy
small parts of the brain without affecting other parts. When we see the results, we can
understand the importance of that section of the brain. Scientists can also use magnetic,
chemical, and electric energy to stimulate certain parts of the brain and observe the results on
the human being.
When our brain works, the brain cells (neurons) communicate with electric impulses.
These impulses can be detected with certain machines in order to study the patterns in our
mental processing. An EEG (electroencephalogram) helps us interpret these brain waves that
result from the electric impulses. If a scientist wants to see the effect of a certain stimulus (for
example a loud noise) on a person, the scientist can observe the patterns of brain activity that
can be shown on the EEG, and pinpoint the exact location of activity, and hence the section of
the brain that is responsible for processing this stimuli.
Some more of these machines include:
-The CT scan, which is a series of X ray photographs.
-PET scan, which shows the brain's activity by visualizing the amount of fuel each
cell consumes (glucose).
-MRI which uses magnetic fields and radio waves to produce images.
* The brain has no sensory receptors. This means injury or electric shock to the brain does not
cause pain.
2
Some of the most basic parts of the brain, upon which more complex systems are
founded are found in most mammals. The brain is comprised of many key components:
The brainstem starts where the spinal cord connects to the brain.
The medulla is the base of this brainstem, and is responsible for basic involuntary
functions like breathing and heartbeat.
Just above the medulla is the pons, which helps coordinate movements.
*The brainstem is a crossover point. This means that most nerves to and from each side of the
brain connect with the body's opposite side, and this is where those nerves "switch over."
Inside the brainstem is the reticular formation. This net-like structure is a network of
nerves and plays an important role in controlling arousal.
The thalamus is the brain's sensory switchboard. It sits at the top of the brainstem, and
is a "joined pair of egg-shaped structures." It receives information from all the senses
and relays them to more complex and specialized areas of the brain.
The cerebellum is almost the size of a baseball. It is responsible for coordinating movement
and balance, and it also helps process sensory input.
The limbic system is associated with emotions and motivation. It is a neural system that
contains many emotion-related parts:
-Amygdala influences aggression and fear
-Pituitary Gland secretes hormones
-Hypothalamus maintains homeostasis (keeps the body's state stable)
-Hippocampus linked to memory
3
The cerebral cortex is a thin layer of interconnected neural cells that covers the two
hemispheres of the cerebrum (the section of the brain that constitutes 85% of its weight).
The cerebral cortex forms "wrinkles" and is not a flat surface. This is primarily to give it more
surface area for neurons.
Nerve cells (neurons)
Glial cells are cells that support, maintain, and provide nourishment to the neurons.
*Each hemisphere (half) of the brain is divided into 4 lobes. (refer to diagram for position)
-frontal lobes: speaking, muscle movements, making plans and judgments
[motor cortex: behind frontal lobes, controls voluntary movements.]
-parietal lobes: receives sensory input for touch and body position
[sensory cortex: front of parietal lobes, registers and processes touch &
movement sensations.]
-occipital lobes: receives information from the visual (sight) fields
-temporal lobes: includes auditory areas (hearing)
Association areas are parts of the cerebral cortex that are not involved in primary motor or
sensory functions, but are involved in higher mental functions such as learning, remembering,
thinking, and speaking.
Language
Many different parts of the brain are combined in order to produce what we define as language.
Language involves moving your mouth to speak, interpreting auditory messages to understand
what others are saying, and translating the visual images we see when we read to meaningful
things. We use our motor cortex to move as we speak, our visual cortex to read words we see,
and a few other key parts:
-Broca's area - in the left frontal lobe, directs muscle movements involved with speech.
-Wernicke's area- in the left temporal lobe, controls language reception (auditory)
*Aphasia is an impairment of language that occurs when one of these areas is damaged.
The Brain's Plasticity
Our brain has the ability to change. The neural connections that we're born with don't
always stay the same forever. If part of the brain is damaged, new connections can form to make
up for it. For example, the nerve cells in our head can die off and be replaced. The formation of
new neurons is called neurogenesis. Sometimes, an entire hemisphere of the brain can be
removed (to prevent seizures) and the patients are still able to function, because the brain forms
new pathways to replace the damaged or removed ones. The brain isn't like a computer, it's like
the Malden transportation system. While many bus routes might be cut off, people will still find
other ways to get from one place to another.
4
Each hemisphere of the brain is responsible for different things. They might look alike,
but their functions are not identical. The two hemispheres are connected by a band of nerual
fibers called the corpus callosum.
In some medical procedures, the corpus callosum has been cut. This results in a
separation between the two hemispheres. Without the communication between the two
hemispheres, people have different experiences. For example, when one looks at a picture
divided in half, each eye sends the image on its own side to the opposite hemisphere. Then, when
a person is told to say what he saw (using the speech on the left hemisphere) he would say what
was on the right side. When asked to point to what he saw (using the optic on the right
hemisphere) he would point to the image that was on the left side. This condition is
unsurprisingly called a split brain.
5
One of the most researched topics in psychology is consciousness. Consciousness is
our awareness of ourselves and our environment. Perception, memory, thinking, language, and
attitudes all operate on two levels- a conscious, deliberate level, and a subconscious, hidden
level. This "two track" concept is called dual processing. It states that everything we do is
processed in the brain not on one path, but on multiple. Beneath the surface, unconscious
information processing occurs simultaneously on many parallel tracks.
Review Questions
 What are the important lower level brain structures and what do they do?
 What are the parts of the limbic system and what do they do?
 What are the lobes in the cerebral cortex hemispheres and what do they do?
 What tools do scientists use to study the brain?
 What brain areas are involved in language processing?
 What is neuroplasticity? (Brain plasticity)
 What type of thinking is each hemisphere of the brain involved in? What do split brains
reveal about the functions of each hemisphere?
 Explain dual-processing.