and related symptoms that contribute to cogni-
tion, improving the person’s overall ability to
engage in cognitive activities.
Risk Factors and Preventive Measures
Brain damage resulting from stroke or TBI is the
leading cause of cognitive dysfunction among
adults in the United States. Preventive measures
that target these events correspondingly lower the
likelihood of cognitive dysfunction. For stroke
such measures include appropriate treatment for
HYPERTENSION(high BLOOD PRESSURE) and DIABETES,
the leading causes of stroke. For TBI such meas-
ures include appropriate protective devices such as
seat belts in vehicles and helmets for activities that
entail risk for contact injuries to the head.
There is some evidence that the herbal supple-
ment GINKGO BILOBAhelps maintain alertness and
cognitive function in people who are healthy and
may improve concentration and cognition in peo-
ple who have mild forms of cognitive dysfunction
or memory impairment. However, neither pre-
scription medications nor herbal products have
the ability to fully restore cognitive functions lost
to permanent brain damage such as occurs with
Alzheimer’s disease or TBI.
See also ENCEPHALOPATHY; MEMORY AND MEMORY
IMPAIRMENT.
coma A sustained state of loss of CONSCIOUSNESS
from which a person cannot be aroused. When in
a coma a person does not respond to any external
stimuli, including PAIN. REFLEXresponses may or
may not be present, depending on the depth of
the loss of consciousness. Some comas are
reversible with immediate and appropriate med-
ical intervention. However, irreversible coma typi-
cally leads to PERSISTENT VEGETATIVE STATEorBRAIN
DEATH.
COMMON CAUSES OF COMA
BRAIN HEMORRHAGE CARDIAC ARREST
DRUG OVERDOSE ENCEPHALITIS
excessive ALCOHOLconsumption hepatic ENCEPHALOPATHY
HYPERGLYCEMIA hypoglycemia
STROKE toxic exposure
TRAUMATIC BRAIN INJURY(TBI) untreated HYPOTHYROIDISM
UREMIA
Neurologists may use various assessment
approaches, such as the Glasgow Coma Scale or
the Rancho Los Amigos Scale (RLAS), to evaluate
the depth of a coma and the extent of damage to
the BRAINthat the coma represents.
See also ANESTHESIA; DELIRIUM; UNCONSCIOUSNESS.concussion An injury to the BRAIN resulting
from a blow to the head. The blow causes the
brain to jolt against the inside of the cranium
(skull), causing BLOODvessels within the brain tis-
sue to rupture. Often these are small blood vessels
and the bleeding is comparable to that of minor
bruising, though any damage within the brain
may have potentially serious consequences,
depending on its location. Brain tissue may also
swell as a protective response to traumatic injury.
Concussion is the most common head injury.
Symptoms and Diagnostic Path
The symptoms of concussion vary with the sever-
ity of the blow. The symptoms of mild to moderate
concussion typically include- HEADACHE
- dizziness
- confusion or disorientation
- vision changes or disturbances such as “seeing
stars” or seeing double (DIPLOPIA)
- ringing in the ears (TINNITUS)
- brief loss of memory, especially of the incident
causing the concussion
The symptoms of mild to moderate concussion
typically go away in 15 minutes to several hours.
Symptoms that are more extensive suggest severe
concussion and typically include- severe headache
- one pupil larger than the other
- NAUSEAand VOMITING
- drowsiness or inability to stay awake
- persistent confusion
- irritability, agitation, or emotional instability
- weakness on one side of the body
A person may have a reddened area, a bruise,
or swelling at the site of impact, although often244 The Nervous System