Psychology: Chapter 3, Section 2

Note how the size of the cerebrum parallels thought abilities

• The brain can be roughly divided into three parts: the hindbrain, the midbrain, and the forebrain
• Hindbrain: lower portion of brain, involved in mostly involuntary regulation needed for survival: heart rate, respiration, balance
• Midbrain: Involved in vision, hearing and alertness
• Forebrain: front area of brain, involved in complex functions like thought and emotion

• The most important structures of the hindbrain are the medulla, the pons, and the
cerebellum.
• Medulla: Heart rate, blood pressure, breathing
• Pons: In front of the medulla; regulates body movement, attention, sleep, and alertness
• Cerebellum: Balance and coordination

The hindbrain is located at the base of the brain, near where the spinal cord connects to the brain

• Involved in vision and hearing
• Contains reticular activating system, which is important for attention, sleep, and arousal
• Alcohol affects the reticular activating system, reduces alertness and slows down reactions
• Sudden, loud noises stimulate the reticular activating system, thus waking a person up

Though small in size, the midbrain has a lot of important functions

• Four key areas of the forebrain are the
thalamus, the hypothalamus, the limbic
system, and the cerebrum

Parts of the Forebrain: the Thalamus
• The thalamus is a relay station for sensory stimulation
• Sensory messages go through the thalamus to the other areas of the brain, and tells the rest of the brain if that was something painful, pleasurable, hot, or cold that just happened
• The thalamus also sends messages from the eyes or ears to the parts of the brain that can interpret what was just seen or heard

Parts of the Forebrain: the Hypothalamus
• The prefix “hypo” is a Greek prefix meaning
“under” (hypothermia, hypoglycemia, etc.) and is sort of the opposite of “hyper.”
• Hypothalamus is a tiny but important area
“under the thalamus.”
• It regulates body temperature, eating, drinking, aggression, and sexual behavior

Parts of the Forebrain: the Limbic System
• The limbic system is a fringe along the inner edge of the cerebrum.
• Involved in learning, memory, emotion, hunger, sex, and aggression
• Damage to the limbic system can affect memory, where a person can recall vivid childhood memories of a sister, but can’t recall that that sister visited earlier that day
• Damage in another area may make someone especially aggressive or especially passive

Parts of the Forebrain: the Cerebrum
• The cerebrum (Latin for “brain”) is the largest part of the human brain (about 70% of the entire brain)
• Its wrinkled surface is called the cerebral
cortex (cortex is Latin for “bark of a tree”)
• The cerebral cortex handles the brain’s most advanced functions: thinking, memory, language, emotions, perception, complex motor functions, imagination, and much more

• The cerebral cortex is what separates humans from other animals.
• The brain of a chimpanzee, for example, also has a cortex, but in far smaller proportions.
• The cortex allows us to think, to remember, to imagine. Essentially, we are human beings by virtue of our cortex.
• A human’s cerebral cortex, if flattened, would cover four pages of typing paper; a chimpanzee’s would cover only one page; and a rat’s would cover a postage stamp.

• The cerebral cortex is composed of two sides: the left side and the right side
• Each of these sides is called a hemisphere
• Generally, the left hemisphere controls the right side of the body, and vice versa

• The structure that connects the two hemispheres is called the corpus callosum
• The corpus callosum is essential to allow the two hemispheres to communicate with each other
• The corpus callosum may be severed in the case of chronic epileptic seizures

• There are four lobes of the cerebral cortex: the frontal, parietal, temporal, and occipital
• The frontal lobe is right behind the forehead
• The parietal lobe is on the top and rear of the head
• The temporal lobe is on the side, just below the ears
• The occipital lobe is in the back

• Vision is sensed by the occipital lobe in the back of the brain
• A strike at the back of the head can cause a seeming flash of light
• Damage to the occipital lobe can cause problems with recognizing close friends

Note how the right visual field ends up in the left side of the brain, and vice versa

Senses and Motor Behavior: Hearing
• Hearing is processed in the temporal lobe (on the sides below the ears)
• Sound goes from our ears to the thalamus to the auditory area of the temporal lobe
• If there is damage to this area of the temporal lobe, a person may have trouble recognizing common sounds

• Signals from the right ear travel to the auditory cortex located in the temporal lobe on the left side of the brain, and vice versa.
• The auditory cortices sort, process, interpret and file information about the sound.
• The comparison and analysis of all the signals that reach the brain enable you to detect certain sounds and suppress other sounds as background noise.
Traveling to the Brain

Senses and Motor Behavior: Skin Senses
• Skin senses include touch, warmth, cold, and pain
• The senses are projected into the sensory cortex of the parietal (top) lobe
• There are slightly different areas of the parietal lobe that handle individual senses (a pain area, a touch area, etc.)
• See page 62 in your book for a helpful diagram of this phenomenon

• Association areas coordinate all the incoming messages into a comprehensible message
• Some sensory areas of the brain only respond to horizontal lines while others only respond to vertical lines
• Association areas can put all these messages into one comprehensible picture of a box, a map, a refrigerator, or whatever it is

• The association areas in the frontal lobes near the forehead could be called the executive center
• Executive decisions, such as solving problems and making plans occur here
• This area combines all incoming information, memories, moral values, etc., so that a single decision can be made

• Many functions occur in both hemispheres of the brain
• However, language functions occur in the left hemisphere for almost all right-handed people and 2/3 of left-handed people
• There are two key language areas in that hemisphere: Wernicke’s area and Broca’s area

• Located in the temporal lobe
• Puts together sounds and sights
• People with damage to this area may have difficulty understanding speech, and their speech doesn’t make much sense
• When one person tried to describe a picture of two boys taking cookies behind a woman’s back, she replied, “Mother is away her working her work to get her better, but when she’s looking the two boys looking the other part. She’s working another time.”

• Broca’s area is located in the frontal lobe near the motor cortex that controls the areas of the face used for speaking
• When Broca’s area is damaged, people speak slowly and under some difficulty, using simple sentences

• Occasionally, people have needed to have their corpus callosum to be severed; for example, if they suffer from severe epilepsy
• This severing reduces the spread of seizures
• It also produces interesting insight into the two hemispheres
• A person may be able to say verbally what is in the right hand, but not in the left hand, because the right side of the brain lost communication with the language center

• There are several ways we can find out more about how the brain works, including accidents, electrical stimulation, EEGs and scans
• Accidents: Damage can tell us about areas of function based on what is damaged and what skills are lost
• Recount the story of Phineas Gage. What did we learn from his experience?

• Electrical Stimulation of the Brain: If a scientist directly applies a small amount of electricity to an area of the brain, the subject may report seeing light, or hearing a sound, or feeling pleasure or pain
• Electroencephalogram (EEG): Records electrical activity already going on in brain (does not apply any electricity to brain)
• Scans: CAT Scans uses x-rays, MRI uses magnetism and gets better images than CAT scans, and PET and fMRI scans can show the brain at work, rather than just a snapshot