M

memory and memory impairment The abilities
to recall past events and to anticipate future
events are hallmarks of the human experience
and their diminishment an indication of various
disorders that affect BRAINfunction. Memory is the
process by which the brain stores and retrieves
information. Memory impairment may affect the
processes of memory storage, memory retrieval, or
both, and may be temporary or permanent.

Mechanisms of Memory Storage and Retrieval
The brain manages memories through multiple
processes, both organic and functional, that
involve numerous areas of its lobes and structures.
Most researchers believe the brain stores memo-
ries in bits and fragments, which it then reassem-
bles when recalling a specific memory. Cognitive
processes (thought and analysis) and emotion sig-
nificantly shape memory storage and recall, even,
some experts believe, to the extent of causing
memory errors and false memories. Such memory
mistakes can occur when the brain blends events
in the processes of storing and retrieving. Accord-
ingly, there is much controversy among medical as
well as legal professionals about the objectivity
and precision of memory.
Storing memories begins with sensory or emo-
tional NERVEimpulses that travel to the brain. Dif-
ferent areas of the brain receive, interpret, and
encode (prepare for storage) the various kinds of
nerve impulses that arrive. Memory is either
short-term (transient) or long-term (relatively
permanent). Bridging the two is working memory,
through which the brain encodes information to
allow its storage in long-term memory. The extent
to which a person gives attention to incoming
information helps determine whether and how
the information enters memory. The hippocam-

pus, an area of the temporal lobe, is essential for

forming new memories. The hippocampus also is

the area of the brain responsible for emotion and

emotional expression.

The mechanisms of short-term memory—infor-

mation the brain retains for seconds to minutes,

such as the name of the waiter taking a menu

order or the amount of a purchase—appear to cre-

ate only temporary shifts in neuronal connections.

The information has transient (and often time-

limited) value so the brain gives it transient atten-

tion. The mechanisms of long-term memory—

memory of events and people from days to

decades ago—create permanent changes in the

neuronal pathways among cells in the regions of

the brain that participate in memory storage and

retrieval. Once formed, these pathways appear to

remain intact and fully functional even when

there is no retrieval for extended periods of the

memories they connect.

Researchers categorize long-term memory as

either explicit (also called declarative) or implicit

(also called nondeclarative or procedural). Explicit

memory requires conscious attention to recall

information, such as when taking a test or telling

the story of a childhood event. Explicit memory

appears to involve primarily the frontal, temporal,

and parietal lobes of the cerebral cortex. Implicit

memory contains information the brain retrieves

and acts on automatically, without conscious

attention. Riding a bicycle, playing a musical

instrument, driving a car, and throwing a ball are

common functions of implicit memory. Implicit

memory involves primarily the prefrontal cerebral

cortex and the cerebellum, which coordinate vol-

untary MUSCLEactivity, and the amygdala, a small

almond-shaped structure in front of the hip-

pocampus that governs fear and fear response.

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