stroke.
A brain tumor is an anomalous, abnormal proliferation of cells in
the brain. Such anomalous growth may be either benign (nonspread-
ing) or malignant (able to metastasize and spread); the latter type
of tumor has a much poorer prognosis. The abnormal tissue growth
often disturbs the normal functioning of nearby neural tissue, pro-
ducing symptoms that may manifest as changes in perception, other
mental function, or behavior.
Another cause of brain lesions is physical trauma resulting from
injury to the head. Head injuries may be of two general types: closed
or penetrating. Closed head injury occurs when there is a whack of
some kind to the head, or even a sudden powerful acceleration or
deceleration. In such cases, the integrity of the skull is not broken and
the brain is not penetrated from the outside. Sometimes this is called
a concussion. Damage to the brain may occur from shearing forces
within the tissue or internal contact with the bone. Internal swelling
may also occur. Most head injuries are of this type. In a penetrating
head injury, the integrity of the skull is compromised and the brain
comes into direct contact with an external agent of damage.
Finally, certain diseases are associated with identifiable lesions in
the brain. One of the best-studied examples is Parkinson’s disease, a
neurodegenerative condition characterized by slowness and difficulty
with movement. Parkinson’s disease is associated with neuronal
death in a specific region of the brain: the substantia nigra, one of the
clusters of cells in the brainstem that uses dopamine as a neurotrans-
mitter.
To make connections between regions of the brain and specific func-
tions, it is necessary to identify as precisely as possible the location of
a brain lesion and then match that with symptoms exhibited by the