286 ChaPteR 8 Memory
the responsibility of the cerebral cortex (Battaglia
et al., 2011). In fact, memories may be stored
in the same cortical areas that were involved in
the original perception of the information: When
people remember pictures, visual parts of the brain
become active; when people remember sounds,
auditory areas become active, just as they did when
the information was first perceived (Nyberg et al.,
2000; Thompson & Kosslyn, 2000).
The typical “memory” is a complex cluster
of information. When you recall meeting a man
yesterday, you remember his greeting, his tone
of voice, how he looked, and where he was. Even
a single concept, such as shovel, includes a lot of
information about its length, what it’s made of,
and what it’s used for. These different pieces
of information are probably processed separately
and stored at different locations that are distrib-
uted across wide areas of the brain, with all the
sites participating in the representation of the
event or concept as a whole. The hippocampus
may somehow bind together the diverse aspectsA team of researchers has identified how neu-
rons in the hippocampus may become involved in
specific memories. They implanted tiny needle-
shaped electrodes into the brains of 13 people
about to undergo surgery for severe epilepsy.
(This is standard procedure because it enables
doctors to pinpoint the location of the brain
activity causing the seizures.) As the patients were
being prepped, they watched a series of 5- to
10-second film clips of popular shows such as
Seinfeld or The Simpsons, or of animals and land-
marks. The researchers recorded which neurons
in the hippocampus were firing as the patients
watched; for each patient, particular neurons
might become highly active during particular
videos and respond only weakly to others. After
a few minutes, the patients were asked to recall
what they had seen. They remembered almost
all of the clips, and as they recalled each one, the
very neurons that had been active when they first
saw it were reignited (Gelbard-Sagiv et al., 2008).
The formation and retention of procedural
memories (memory for skills and habits) seem to
involve other brain structures and pathways. In
work with rabbits, Richard Thompson (1983, 1986)
showed that one kind of procedural memory—a sim-
ple, classically conditioned response to a stimulus,
such as an eye blink in response to a tone—depends
on activity in the cerebellum. Human patients with
damage in the cerebellum are incapable of this type
of conditioning (Daum & Schugens, 1996).
The formation of declarative and procedural
memories in different brain areas could explain a
curious finding about patients like H. M. Despite
their inability to form new declarative memories,
with sufficient practice such patients can acquire
new procedural memories that enable them to
solve a puzzle, read mirror-reversed words, or play
tennis—even though they do not recall the train-
ing sessions in which they learned these skills.
Apparently, the parts of the brain involved in ac-
quiring new procedural memories have remained
intact. These patients also retain some implicit
memory for verbal material, as measured by prim-
ing tasks, suggesting that the brain has separate
systems for implicit and explicit tasks. As Figure 8.6
shows, this view has been bolstered by brain scans,
which reveal differences in the location of brain
activity when people with healthy brains perform
explicit versus implicit memory tasks (Reber, Stark,
& Squire, 1998; Squire et al., 1992).
The brain circuits that take part in the forma-
tion and retrieval of long-term memories, however,
are not the same as those involved in long-term
storage of those memories. Although the hippocam-
pus is vital for the formation and retrieval of mem-
ories, the storage of memories eventually becomesFiguRE 8.6 Brain Activity in Explicit and implicit
Memory
As these composite functional MRI scans show, pat-
terns of brain activity differ depending on the type of
memory task involved. When people had an explicit
memory for dot patterns they had seen earlier, areas in
the visual cortex, temporal lobes, and frontal lobes (in-
dicated by orange in the lower photos) were more ac-
tive. When people’s implicit memories were activated,
areas in the visual cortex (blue in the upper photos)
were relatively inactive (Reber, Stark, & Squire, 1998).