192 • CHAPTER 7 Long-Term Memory: Encoding and Retrieval
Other structures in the MTL are also important. Let’s consider, for example, the
perirhinal cortex, which was studied along with the hippocampus in an experiment by
Lila Davachi and coworkers (2003). The study was designed to determine how these
structures responded as the names of objects were presented in the encoding part of a
memory experiment.
The procedure for this experiment is shown in ● Figure 7.18. Participants, who
were in a brain scanner, viewed a series of 200 words. They were instructed to create an
image of a specifi c place that went with each word. For example, if the word was dirty,
they could create an image of a garbage dump.
Twenty hours later, the participants were presented with a recognition test in which
they saw the same 200 words they had seen earlier, along with a new set of 200 words.
During this part of the experiment, they were not in the brain scanner. Their task was
to indicate which of the words they had seen before, so a correct answer would be
“old” when an old word was presented, and “new” when a new one was presented (see
Method: Recognition Memory, Chapter 6, page 154). Davachi found that participants
remembered 54 percent of the old words (they said “yes” to an old word) and forgot
the remaining 46 percent (they said “no” to an old word).
Davachi then determined whether there was any difference between the brain
activity that had been recorded in the scanner during encoding for the remembered
and forgotten words. The results, shown in ● Figure 7.19a, indicate that activity in
the perirhinal cortex was greater for the remembered words than for the forgot-
ten words. Thus, in the perirhinal cortex, words that generated more activity during
encoding were more likely to be familiar to the participants during the recognition
test (“I saw that word before”). This result confi rms physiologically what we have
seen behaviorally: What happens during encoding affects the chances that memory
will occur during retrieval.
Notice that this difference between remembered and forgotten words did not
occur in the hippocampus (Figure 7.19b). This doesn’t mean that the hippocampus
isn’t involved in memory. As we have seen from the case of H.M., the hippocam-
pus is crucial for memory. Other experiments have shown that the hippocampus is
important for aspects of memory other than recognition, such as remembering the
context within which an object appears (Davachi et al., 2003). In addition, as we
will see in the next section, the hippocampus plays a crucial role in forming new
memories.
Other structures in the MTL are also involved in memory. The parahippocampal
area is important for remembering spatial information (in Chapter 2, page 32, we saw● FIGURE 7.18 Design of
Davachi’s experiment. During
encoding, participants in a scanner
created images in their mind in
response to words. During retrieval
20 hours later, the participants’ task
was to recognize the words they had
seen.Cue on
reverse side:
“DIRTY” Participant not in scannerCreate image of place to match
words while brain is being scanned.20-hour delay
Recognition testCopyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.