Content Standard A:
Formulate and revise scientific explanations and models using logic and evidence.

Content Standard A:
Scientists rely on technology to enhance the gathering and manipulation of data.

Content Standard C:
Organisms have behavioral responses to internal changes and to external stimuli.

1. Tell students that one of the ways that scientists investigate the function of the living human brain is by using positron emission tomography (PET). The PET images that the students will examine use radioactive glucose to identify parts of the brain that are active. Active brain areas use more glucose than less active areas and thus more of the labeled glucose is taken up into the active areas. PET scans are color-coded. The scale bar shown on Master 1.1, Positron Emission Tomography (PET) Images, provides a reference. The most active brain areas are shown in red. Areas in yellow are less active than areas in red, but are more active than areas in green. The least active areas are shown in blue or purple.

PET images are color-coded by computer to show activity in the brain. This is similar to color-coded images students may have seen on television weather reports. In weather radar images, areas encountering heavy storms appear in red and yellow, and areas experiencing milder weather disturbances appear in green or blue.

2. Divide the class into groups of three students. Give each group a copy of Master 1.1, Positron Emission Tomography (PET) Images, and a copy of Master 1.2, Interpreting PET Images.
3. Help students understand how the PET images correlate to the orientation of the brain in the body.

The PET images show a cross-section of the brain. The four images in each set show four different levels of the brain. In these images, the front of the brain is toward the top (the subject’s face is toward the top of the image). Have the students examine the PET scans and identify the regions that become active in response to each stimulus.

Content Standard A:
Communicate and defend a scientific argument.

4. Instruct students to work with their group members to answer the questions on Master 1.2. When students reach question 5, display a transparency of Master 1.3, PET Image Tasks, to provide the needed information.
5. Discuss the answers to the questions on Master 1.2 as a class.

Sample answers for the questions on Master 1.2 are listed in the procedure for the online version of Activity 2.

Content Standard C:
Cells can differentiate and complex multicellular organisms are formed as a highly organized arrangement of differentiated cells.

Assessment:
Remember, the names of the parts of the brain are not the important concepts that students need to learn. Rather, this is a way for students to relate what they have learned about localization of brain function to other activities and thus reinforce the concept that different brain regions control different functions.

1. Display transparencies of Master 1.4, Major Regions of the Brain, and Master 1.5, Areas of the Cerebral Cortex and Their Function.
2. Ask students to take out their completed worksheet on Master 1.2. Review the tasks that the students performed in Step 1 of Activity 1 and ask students to identify the part of the brain that was active in each case.

From the information in question 5 on Master 1.2, students should be able to identify the brain area involved in some of the tasks performed in Step 1 of Activity 1, but others were not covered in that question. Also, for some of the activities listed, more than one function is involved. For example, reciting the Pledge of Allegiance requires both memory and speech. Be aware that this chart is very simplified. Virtually all mental functions involve more than one brain area.

Content Standard A:
Scientists rely on technology to enhance the gathering and manipulation of data.

Content Standard C:
Multicellular animals have nervous systems that generate behavior.

Content Standard G:
Usually, changes in scientific knowledge occur as small modifications in extant knowledge.

1. Give each student a copy of Master 1.6, What Happened to Phineas Gage? Instruct students to read the story and answer the questions.

Phineas Gage was injured in an accident in the 1800s. His recovery from the injury and the resulting change in personality and behavior gave scientists new insight into brain function.^8,9

Figure 1.8: Computer reconstruction of the skull of Phineas Gage illustrating the projection of the tamping rod through the brain. Reprinted with permission from Damasio, H., et al. 1994. The return of Phineas Gage: Clues about the brain from a famous patient. Science 264:1102–05.

Sample Answers to Questions on Master 1.6

Question 1. How did Phineas Gage change after the accident?

After the accident, Gage’s personality changed. He was no longer the likeable and responsible person he was before the accident. Instead he was irresponsible and used profanity.

Question 2. How did Phineas Gage’s accident change scientists’ understanding of the brain?

Scientists learned that the brain does more than control language and movement. It also controls emotions and social behaviors. Equally important, scientists learned that the brain processes information for specific functions in specific brain areas.

Content Standard C:
Multicellular organisms have nervous systems that generate behavior.

Content Standard F:
An individual’s mood and behavior may be modified by substances.


Assessment:
If students understand that PET images reveal changes in brain activity and that drugs activate the reward system in the brain, students should predict that the reward system (the VTA and nucleus accumbens) should be more active after an individual takes drugs. These brain areas should appear red or yellow in PET scans taken after drug use, whereas they would be purple or blue in PET images taken before drug use.

1. Now that students understand that different areas in the brain process specific types of stimuli, ask students to consider things that make them feel good, or are pleasurable. How might doing something pleasurable change brain activity?

If students understand, from Activity 2 of this lesson, that brain functions are localized to specific brain areas, they should suspect that things that make them feel pleasure will stimulate a specific brain region.

2. Display the transparency of Master 1.7, The Reward System. Tell students that part of the brain produces and regulates feelings of pleasure, which scientists call reward. This brain region is called the reward system. The parts of the brain that make up the reward system are the ventral tegmental area (VTA), the nucleus accumbens, and part of the frontal region of the cerebral cortex. This brain region responds to life-sustaining activities such as eating and drinking, as well as species-sustaining sexual activity.
3. Introduce students to the idea that drugs of abuse activate the brain’s reward system, or pleasure circuit. Drugs alter the way the reward system functions. Drugs also act on other regions of the brain, but their action in the reward system makes the person abusing drugs feel pleasure and want to continue taking drugs.

Students will learn more about how drugs exert these effects in the remaining lessons in this curriculum supplement.

4. Ask students to hypothesize how PET images of a person’s brain would change after taking drugs of abuse.

Students may predict an increase in activity in the reward system of the brain. Currently, though, PET technology is not sensitive enough to allow scientists to visualize this reward-system activation. The VTA and nucleus accumbens are too small for PET images to detect significant activity changes. Scientists have relied on other technologies to learn that drugs of abuse do activate these brain regions.

Some students may hypothesize that PET images of the brain after drug abuse would also show changes in other regions of the brain. This is correct. Drugs do affect other regions of the brain, but it is the reward system that triggers the pleasurable feelings associated with drug use. More information on the more widespread effects of drugs on the brain is presented in Lesson 4.