The amygdala also appears to be where face recog-
nition, in conjunction with emotional associations
such as love or fear, takes place.
Memory retrieval requires activating, or stimu-
lating, the neuronal pathways that connect the
stored information. This involves interactions
among neurotransmitters, hormones, and electri-
cal impulses, though precisely how these interac-
tions 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 informa-
tion. Such forgetfulness may range from the
names of newly introduced people to where the
car keys are or the driving route to give a co-
worker a ride home. Many researchers believe
such forgetfulness represents an incompletion in
the brain’s processes for establishing neuronal
pathways. Only when information becomes repe-
titious 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 neu-
ronal 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 espe-
cially effective without the other. Correspond-
ingly, cognitive dysfunction and memory
impairment often occur together. Because
researchers do not fully understand the mecha-
nisms 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 forget-
fulness tends to become more common as people
get older, significant memory impairment is notan
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 DISEASEandDEMENTIA, almost exclu-
sively occur in people over age 60.
Circumstances that can affect memory in peo-
ple of any age include BRAIN TUMOR, INFECTIONsuch
as ENCEPHALITISor MENINGITIS, systemic neurologic
conditions such as MULTIPLE SCLEROSIS, and disor-
ders 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 underly-
ing 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 STROKEorTRAU-
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)Amnesiaand memory lossare common terms for
disturbances of memory. Amnesia is the inability
to recall past information or to remember infor-
mation relevant to the future, such as appoint-
ments. Amnesia may result from the inability tomemory and memory impairment 261