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The Biochemistry of Memory

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The Biochemistry of Memory
234
Chapter 6
Memory
evidence available to carefully and critically examine claims of recovered memories
while keeping in mind the possibility that constructive memory processes might have
influenced those memories. This careful, scientific approach is vital if we are to protect
the rights of those who report recovered memories, as well as those who face accusations arising from them.
LINKAGES
Where are memories stored?
(a link to Biology and Behavior)
Biological Bases of Memory
䉴 How does my brain change when I store a memory?
Many psychologists who study memory focus on explicit and implicit mental processes
(e.g. Schott et al., 2005). Others explore the physical, electrical, and chemical changes that
take place in the brain when people encode, store, and retrieve information (Abraham,
2006; Jonides, Lacey, & Nee, 2005; Fields, 2005).
The Biochemistry of Memory
As described in the chapter on biology and behavior, communication among brain cells
takes place at the synapses between axons and dendrites, using chemicals called neurotransmitters that are released at the synapses. The formation and storage of new memories are associated with at least two kinds of changes in synapses.
The first kind of change occurs when stimulation from the environment promotes
the formation of new synapses. Scientists can now actually see this process occur. As
shown in Figure 6.13, repeatedly sending signals across a particular synapse increases
the number of special little branches, called spines, that appear on the receiving cell’s
dendrites (Lang et al., 2004; Toni et al., 1999). The second kind of change occurs as
new experiences change the operation of existing synapses. For example, when two neurons fire at the same time and together stimulate a third neuron, that other neuron will
later be more responsive than before to stimulation by either neuron alone. This process
of “sensitizing” synapses is called long-term potentiation (Li et al., 2003; Rioult-Pedotti,
Friedman, & Donoghue, 2000). Other patterns of electrical stimulation can weaken
synaptic connections, a process called long-term depression (Malenka, 1995). Changes
in the sensitivity of synapses could account for the development of conditioned
responses and other types of learning (Olson et al., 2006).
In the hippocampus (see Figure 6.14), these changes appear to occur at synapses that
use the neurotransmitter glutamate (Malenka & Nicoll, 1999). Other neurotransmitters,
such as acetylcholine, also play important roles in memory formation (e.g., Furey,
FIGURE
6.13
Building Memories
These models are based on electron microscope images of synapses in the brain. The
model on the left shows that, before signals were repeatedly sent across the
synapse, just one spine (shown in white)
appears on this part of the dendrite. Afterward, as shown in the other model, there
are two spines, which helps improve communication across the synapse. The creation
and changing of many individual synapses
in the brain appears to underlie the formation and storage of new memories.
Source: Toni et al. (1999).
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