new england journal
n engl j med
Andrew E. Budson, M.D., and Bruce H. Price, M.D.
From the Geriatric Research Education
Clinical Center, Edith Nourse Rogers Me-
morial Veterans Hospital, Bedford, Mass.,
the Department of Neurology, Boston Uni-
versity, Boston, and the Department of
Neurology, Division of Cognitive and Be-
havioral Neurology, Brigham and Wom-
en’s Hospital, Boston (A.E.B.); and Har-
vard Medical School, Boston, and McLean
Hospital, Belmont, Mass. (B.H.P.). Address
reprint requests to Dr. Budson at GRECC,
Bldg. 62, Rm. B30, Edith Nourse Rogers
Memorial Veterans Hospital, 200 Springs
Rd., Bedford, MA 01730, or at abudson@
N Engl J Med 2005;352:692-9.
Copyright © 2005 Massachusetts Medical Society.
emory function is vulnerable to a variety of pathologic
processes including neurodegenerative diseases, strokes, tumors, head trau-
ma, hypoxia, cardiac surgery, malnutrition, attention-deficit disorder, de-
pression, anxiety, the side effects of medication, and normal aging.
As such, memory
impairment is commonly seen by physicians in multiple disciplines including neurol-
ogy, psychiatry, medicine, and surgery. Memory loss is often the most disabling feature
of many disorders, impairing the normal daily activities of the patients and profoundly
affecting their families.
Some perceptions about memory, such as the concepts of “short-term” and “long-
term,” have given way to a more refined understanding and improved classification
systems. These changes result from neuropsychological studies of patients with focal
brain lesions, neuroanatomical studies in humans and animals, experiments in animals,
positron-emission tomography, functional magnetic resonance imaging, and event-
Memory is now understood to be a collection of mental abilities that depend on sev-
eral systems within the brain. In this article, we will discuss the following four memory
systems that are of clinical relevance: episodic memory, semantic memory, procedural
memory, and working memory (Table 1). We will summarize the current understand-
ing of memory from the point of view of functional neuroimaging and studies of pa-
tients with brain insults, which should aid clinicians in the diagnosis and treatment of
the memory disorders of their patients. As therapeutic interventions for memory disor-
ders become available, clinicians will increasingly need to be aware of the various mem-
ory systems in the brain.
A memory system is a way for the brain to process information that will be available
for use at a later time.
Different memory systems depend on different neuroanatomical
structures (Fig. 1 and 2). Some systems are associated with conscious awareness (ex-
plicit) and can be consciously recalled (declarative),
whereas others are expressed by a
change in behavior (implicit) and are typically unconscious (nondeclarative). Memory