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Brain Structures and Memory

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Brain Structures and Memory
235
Biological Bases of Memory
FIGURE
6.14
Brain Structures Involved in
Memory
Combined neural activity in many parts of
the brain allows us to encode, store, and
retrieve memories. The complexity of the
biological bases of these processes is
underscored by research showing that
different aspects of a memory—such as
the sights and sounds of some event—are
stored in different parts of the cerebral
cortex.
Cerebral
cortex
Thalamus
Hippocampus
Cerebellum
Pietrini, & Haxby, 2000; Li et al., 2003). The memory problems seen in Alzheimer’s
patients are related to a lack of neurons that use acetylcholine and send fibers to the
hippocampus and the cortex (Muir, 1997). Drugs that interfere with the action of
acetylcholine impair memory, and drugs that increase the amount of acetylcholine in
synapses can improve memory somewhat in aging animals and humans (Pettit, Shao,
& Yakel, 2001; Sirvio, 1999).
In summary, research has shown that the formation of memories is associated with
changes in many individual synapses that, together, strengthen and improve the communication in networks of neurons (Malleret et al., 2001; Rosenzweig & Bennett, 1996).
Brain Structures and Memory
Are the biochemical processes involved in memory concentrated in certain brain
regions, or are they distributed throughout the brain? The latest research suggests that
memory involves both specialized regions where various types of memories are formed
and widespread areas for storage (Takashima et al., 2006).
Studies of how brain injuries affect memory provide evidence about which parts of the brain are involved in various kinds of memory.
For example, damage to the hippocampus, nearby parts of the cerebral cortex, and the
thalamus often results in anterograde amnesia, a loss of memory for any event
occurring after the injury. People who suffer this kind of damage are unable to form
new memories.
The case of H.M. provides a striking example of anterograde amnesia (Milner, 1966).
When H.M. was twenty-seven years old, part of his hippocampus was removed in order
to stop his severe epileptic seizures. After the operation, his long-term and short-term
memory appeared normal, but something was wrong. Two years later, he still believed
that he was twenty-seven. When his family moved into a new house, he couldn’t
remember the new address or how to get there. When his uncle died, he grieved in a
normal way; but soon afterward, he began to ask why his uncle had not visited him.
He had to be repeatedly reminded of the death and, each time, H.M. began the mourning process all over again. The surgery had apparently destroyed the mechanism that
transfers information from short-term to long-term memory. Now in his seventies,
The Impact of Brain Damage
anterograde amnesia A loss of memory for events that occur after a brain
injury.
236
Chapter 6
Memory
A FAMOUS CASE OF RETROGRADE
AMNESIA After Ralf Schumacher
slammed his race car into a wall during
the United States Grand Prix in June of
2004, he sustained a severe concussion
that left him with no memory of the
crash. Retrograde amnesia is relatively
common following concussions, so if you
ride a bike or a motorcycle, wear that
helmet!
retrograde amnesia A loss of memory
for events that occurred prior to a brain
injury.
H.M. lives in a nursing home, where his only long-term memories are from fifty years
ago, before the operation. He is still unable to recall events and facts he has experienced since then—not even the names of people he sees every day (Corkin, 2002;
Hathaway, 2002).
Although patients with damage to the hippocampus cannot form new episodic
memories, they may still be able to form implicit memories. For example, H.M.’s performance on a complicated puzzle improved steadily over several days of practice, just
as it does with normal people, and eventually it became virtually perfect. But each time
he tried the puzzle, he insisted that he had never seen it before (Cohen & Corkin, 1981).
A musician with a similar kind of brain damage was able to use his implicit memory
to continue leading choral groups (Vattano, 2000). So it appears that the hippocampus
is crucial in the formation of new episodic memories, but that implicit memory, procedural memory, and working memory are governed by other regions of the brain
(Schott et al., 2005; Squire, 1992).
Retrograde amnesia involves loss of memory for events prior to some brain
injury. Often, a person with this type of amnesia can’t remember anything that took
place in the months or years before the injury (Kapur, 1999). In 1994, head injuries
from a car crash left thirty-six-year-old Perlene Griffith-Barwell with retrograde
amnesia so severe that she forgot virtually everything she had learned about everything and every one she knew over the previous twenty years. She thought she was
still sixteen and did not recognize her husband, Malcolm, or her four children. She
said, “The children were sweet, but they didn’t seem like mine,” and she “didn’t feel
anything” for Malcolm. Her memories of the last twenty years have never fully
returned. She is divorced, but, at last report, she still lives with her children and holds
a job in a bank (Weinstein, 1999).
Unlike Perlene, most victims of retrograde amnesia gradually recover their memories (Riccio, Millin, & Gisquet-Verrier, 2003). The most distant events are recalled first;
then the person gradually regains memory for events leading up to the injury. Recovery is seldom complete, however, and the person may never remember the last few
seconds before the injury. One man received a severe blow to the head after being
thrown from his motorcycle. Upon regaining consciousness, he claimed that he was
eleven years old. Over the next three months, he slowly recalled more and more of his
life. He remembered when he was twelve, thirteen, and so on—right up until the time
he was riding his motorcycle the day of the accident. But he was never able to remember what happened just before the accident (Baddeley, 1982). Those final events were
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