138 • CHAPTER 5 Short-Term and Working Memory
What are the researchers who use these methods to
study working memory and the brain trying to explain?
To answer this question, we have only to look back at
this chapter to appreciate that an important charac-
teristic of memory is that it involves delay or waiting.
Something happens, followed by a delay, which is brief
for working memory; then, if memory is successful, the
person remembers what has happened. Researchers,
therefore, have looked for physiological mechanisms
that hold information about events after they are over.
We will describe the following research, which is
designed to determine where and how this informa-
tion is held in the brain (● Figure 5.23): (1) brain dam-
age—how damage to or removal of the prefrontal cortex
affects the ability to remember for short periods of time;
(2) neurons—how neurons in the monkey prefrontal
cortex hold onto information during a brief delay; and
(3) brain activity—areas of the brain that are activated
by working memory tasks, and how the brains of peo-
ple with good and poor working memory respond to a
working memory task.THE EFFECT OF DAMAGE TO THE PREFRONTAL CORTEX
We have already seen that damage to the frontal lobe (see Figure 5.23) in humans
causes problems in controlling attention, which is an important function of the central
executive (page 136). Early research on the frontal lobe and memory was carried out
in monkeys using a task called the delayed-response task, which required a monkey to
hold information in working memory during a delay period (Goldman-Rakic, 1992).
● Figure 5.24 shows the setup for this task. The monkey sees a food reward in one
of two food wells. Both wells are then covered, a screen is lowered, and then there is
a delay before the screen is raised again. When the screen is raised, the monkey must
remember which well had the food and uncover the correct food well to obtain a
reward. Monkeys can be trained to accomplish this task. However, if their prefrontal
cortex is removed, their performance drops to chance level, so they pick the correct
food well only about half of the time.
This result supports the idea that the prefrontal (PF) cortex is important for hold-
ing information for brief periods of time. In fact, it has been suggested that one rea-
son we can describe the memory behavior of very young infants (younger than about
8 months of age) as “out of sight, out of mind” (when an object that the infant can see● FIGURE 5.23 Cross section of the brain showing some of the key
structures that are involved in memory.Frontal
lobePrefrontal
cortex
AmygdalaHippocampus● FIGURE 5.24 The delayed-response task being administered to a monkey.Monkey observes food in tray Delay ResponseCopyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.