Several types of neurophysiological
changes occur throughout the brain as a result of infarcted
tissue caused by stroke or accident. These include
edema, reduced cerebral blood
flow,
the release of
neurochemicals and diachisis. Diachisis is a
type of post-lesional cerebral shock resulting in sudden
inhibition of function in which there is a diminishment and
possibly a complete loss of functioning in brain areas
distal to the site of lesion. Although areas affected by
diachisis may be far away from the point of original damage,
they are usually connected to the infarcted area by nerve
pathways (Steadman, 1997). The cause of diachisis in
unknown; it may be the result of edema, reduced cerebral
blood flow, the release of neurochemicals or other factors
which have not yet been identified. Because these phenomena
affect areas of the brain beyond the point of original
damage, they explain why patients sometimes display symptoms
that are unexpected in view of site of lesion information.
Swelling or edema
begins two or three days after a cerebral insult. Swelling
occurs only in the area that has been injured. However, as
localized swelling can greatly increase pressure throughout
the whole cranium, the functioning of the entire brain may
be affected. Edema of the brain should begin to decrease by
the beginning of the first week post-injury. As intracranial
pressure returns to normal levels, any behavioral changes
that were caused by the swelling rather than by the brain
injury will disappear.
After an injury, arterial
blood flow
to all lobes in both hemispheres may decrease. This
reduction usually lasts between two and four weeks but may
continue for a longer period of time. As decreased blood
pressure reduces the effectiveness of collateral
circulation, it may cause additional infarction when it
occurs in response to an ischemic stroke.
The brain may
release abnormally large amounts of neurochemicals after an injury. These
substances may cause additional damage throughout the
brain.