Encyclopedia of Health and Medicine

memory and memory impairment 261
The amygdala also appears to be where face recognition,
in conjunction with emotional associations
such as love or fear, takes place.
Memory retrieval requires activating, or stimulating,
the neuronal pathways that connect the
stored information. This involves interactions
among neurotransmitters, hormones, and electrical
impulses, though precisely how these interactions
happen remains a mystery. Some memory
retrieval occurs in response to external cues and
stimuli, such as responding to questions or seeing
a familiar face. Implicit memory retrieval appears
activated by exposure to a circumstance, for
example getting on a bicycle or behind the wheel
of a car. Explicit memories are more complex.
Those with strong emotional connections seem
more rapidly and vividly recalled.
Causes of Memory Impairment
Everyone experiences occasional forgetfulness,
most commonly with respect to recent information.
Such forgetfulness may range from the
names of newly introduced people to where the
car keys are or the driving route to give a coworker
a ride home. Many researchers believe
such forgetfulness represents an incompletion in
the brain’s processes for establishing neuronal
pathways. Only when information becomes repetitious
does the brain create connections among
neurons to accommodate it. The more frequently
a person encounters the same information (such
as a person’s name), the more complete the neuronal
connections among the various regions of
the brain that store the information. Forgetfulness
may also represent the brain’s efforts to “clean
house” and maintain efficiency by purging unused
or extraneous information.
Memory impairment occurs when the brain
cannot establish new neuronal pathways to store
new memories or use existing neuronal pathways
to retrieve memories already stored. A person
experiencing memory impairment may be unable
to remember the names of close family members
or how to drive home from the store. Though
memory and cognition (thought and reason) are
distinct functions within the brain, neither is especially
effective without the other. Correspondingly,
cognitive dysfunction and memory
impairment often occur together. Because
researchers do not fully understand the mechanisms
of memory, they do not fully understand
how memory impairment occurs.
The quality of memory, particularly short-term
memory, normally diminishes somewhat with
advanced age (age 70 and beyond). Though forgetfulness
tends to become more common as people
get older, significant memory impairment is not an
inherent dimension of aging. Much age-associated
memory impairment results from conditions that
occur with aging. ATHEROSCLEROSIS, in which plaque
deposits accumulate in the walls of the arteries to
narrow the passageways for BLOOD, is among the
leading causes of impaired memory in older adults.
Neurologic disorders that affect memory, such as
ALZHEIMER’S DISEASE and DEMENTIA, almost exclusively
occur in people over age 60.
Circumstances that can affect memory in people
of any age include BRAIN TUMOR, INFECTION such
as ENCEPHALITIS or MENINGITIS, systemic neurologic
conditions such as MULTIPLE SCLEROSIS, and disorders
that alter the body’s chemical balance such as
LIVER disease or untreated metabolic disorders.
Memory impairment may be transitory (come and
go, such as with a TRANSIENT ISCHEMIC ATTACK [TIA]),
may return when treatment resolves the underlying
cause (such as when the brain heals after an
infection or surgery), or may be permanent
(which occurs when there is tissue damage or loss
in areas of the brain that perform functions of
memory, such as often occurs with STROKE or TRAU-
MATIC BRAIN INJURY [TBI]).
CONDITIONS THAT CAN AFFECT MEMORY
ALZHEIMER’S DISEASE
ATHEROSCLEROSIS (cerebral vascular
BRAIN HEMORRHAGE disease)
CONCUSSION
CREUTZFELDT-JAKOB DISEASE (CJD)
DEMENTIA
ENCEPHALITIS
ENCEPHALOPATHY
HUNTINGTON’S DISEASE
MENINGITIS
ORGANIC BRAIN SYNDROME
PARKINSON’S DISEASE
SEIZURE DISORDERS
STROKE
TRANSIENT ISCHEMIC ATTACK (TIA)
TRAUMATIC BRAIN INJURY (TBI)
Amnesia and memory loss are common terms for
disturbances of memory. Amnesia is the inability
to recall past information or to remember information
relevant to the future, such as appointments.
Amnesia may result from the inability to