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Later experiments located other “pleasure centers” (Olds, 1958). (What the rats actually
experience only they know, and they aren’t telling. Rather than attribute human feelings to rats,
CONNECT 1.4-6 today’s scientists refer to reward centers.) Just how rewarding are these reward centers? Enough
to cause rats to self-stimulate these brain regions more than 1000 times per hour. In other spe-
Tell your students that the neurotrans- cies, including dolphins and monkeys, researchers later discovered other limbic system reward
mitters that work in reward centers are centers, such as the nucleus accumbens in front of the hypothalamus (Hamid et al., 2016).
Animal research has also revealed both a general dopamine-related reward system and
similar to drugs like cocaine and LSD, specific centers associated with the pleasures of eating, drinking, and sex. Animals, it seems,
a topic that is covered in more detail come equipped with built-in systems that reward activities essential to survival. As neuro-
in Module 1.3b. These drugs activate scientist Candice Pert (1986) observed, “If you were designing a robot vehicle to walk into
the reward centers, leading to the the future and survive, . . . you’d wire it up so that behavior that ensured the survival of the
self or the species — like sex and eating — would be naturally reinforcing.”
desire to take the drugs again.

®
AP Science Practice Data Interpretation
TEACH 1.4-6
Teaching Tip Number of Presses
Convey to students that the con- Rats receiving reward center activation Rats not receiving reward center activation
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
nection between survival behavior Trial 1 204 202
and pleasurable sensations makes Trial 2 813 250
evolutionary sense. If behaviors Trial 3 857 300
Copyright © Bedford, Freeman & Worth Publishers.
such as eating, drinking, and sex are Trial 4 900 156
pleasurable, they are more likely to Trial 5 1001 158
be repeated, thus leading to survival. This module describes research on rats that led to the identification of the hypothalamus as a reward center in the brain.
However, in modern times, when food Consider the data set above.
and drink are plentiful, these evolu- • Describe the general difference in number of presses • Calculate the mean for each group.
tionary tendencies can lead to obesity between the groups represented in this table. • Is the variable “number of presses” qualitative or
and addiction. • Describe the trends in the data within each group. quantitative? Explain.
Remember, you can always revisit Unit 0 to review information related to psychological research.

PRACTICE Do humans have limbic centers for pleasure? Some evidence indicates we do. When we
meet likable people or read affirming messages from friends, our brain bursts with reward
center activity (Inagaki et al., 2019; Zerubavel et al., 2018). But when one neurosurgeon
Data Interpretation (SP 3) implanted electrodes in violent patients’ reward center areas, the patients reported only mild
(Times vary) Students will be pleasure. Unlike Olds and Milner’s rats, the patients were not driven to a frenzy (Deutsch,
expected to interpret data from 1972; Hooper & Teresi, 1986). Stimulating the brain’s “hedonic hot spots” (its reward cir-
cuits) produces more desire than pure enjoyment (Kringelbach & Berridge, 2012).
graphs and tables on the AP ® Experiments have also revealed the effects of a dopamine-related reward system in
exam. Therefore, we have included people. For example, experimentally boosting dopamine levels increases the pleasurable
“chills” response to a favorite piece of music, whereas reducing dopamine levels decreases
a Data Interpretation feature. Con- hippocampus a neural center musical-related pleasure (Ferreri et al., 2019). Some researchers believe that many disor-
in the limbic system that helps
sider either assigning this feature process explicit (conscious) dered behaviors may stem from malfunctions in the natural brain systems for pleasure and
for homework or using it as a class memories — of facts and well-being. People genetically predisposed to this reward deficiency syndrome may crave
whatever provides that missing pleasure or relieves negative feelings, such as aggression,
events — for storage.
activity to help students strengthen rich food, or drugs and alcohol (Blum et al., 1996, 2014; Chester et al., 2016).
their skills.
68 Unit 1 Biological Bases of Behavior

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Rats not receiving reward center activation
Answers to Data Interpretation don’t show a pattern of increasing their In Module 3.8a, students will learn about the
Questions presses over the trials. law of effect, which states that behaviors that
• The mean number of bar presses for rats are rewarded are more likely to be repeated,
• Rats receiving reward center receiving reward center activation is 755. and behaviors that are punished are less
activation press the bar a lot more The mean number of bar presses for rats likely to be repeated. Point out to students
than the rats not receiving reward not receiving reward center activation is that this law is supported physiologically by
center activation. 213.2. the discovery of reward centers in the brain.
• Rats receiving reward center • Number of presses is quantitative
activation begin increasing their because it is expressed numerically.
presses after only one trial.

68 Unit 1 Biological Bases of Behavior

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