Memory is the explicit or implicit recall of information
encoded in the recent or distant past. Current
conceptualizations of memory, however, do not view
the construct as a unitary system but rather divide it
into hierarchical taxonomic modules based on duration
of retention and the type of information that
is being retrieved. Among the more fully elucidated
conceptualizations of memory systems is one characterized
by Larry Squire and colleagues, in which
long-term memory is divided into declarative and
nondeclarative subcomponents. Declarative, or explicit,
memory refers to the ability to consciously recall
facts (semantic memory), events (episodic memory),
or perceptual information (perceptual memory).
Nondeclarative memory requires the implicit recall
of information and is usually divided into procedural,
priming, or simple conditioning paradigms. Information
that is retained on the order of seconds or minutes
is usually referred to as short-term memory and
is thought to represent a memory system distinct from
long-term memory. Working memory, which comprises
short-term memory, refers to the short-term
store required to perform certain mental operations
during retention. The following sections examine the
impact of normal aging on different types of memory,
as well as some of the potential moderators and mediators
of cognitive aging. The information presented
is organized hierarchically, following the memory
systems just outlined.
Increased age puts an individual at risk for the
development of neurodegenerative disorders, such as
Alzheimer’s disease (AD). Central to the dementia syndrome
that characterizes AD is the gradual and progressive
loss of long-term memory functions. Although
the vast majority of older adults do not develop
dementia, most experience some degree of cognitive
change. Following the elucidation of memory systems
and their component parts in the cognitive and cognitive
neuroscience literature, there has been a recent
interest in the impact of age on the different memory
systems, independent of the devastating effects of
dementia. Among well-screened individuals who do
not meet diagnostic criteria for dementia, both crosssectional
and longitudinal studies demonstrate that
the different memory component systems do not uniformly age; rather they show differential vulnerability
to aging effects.