Electroencephalogram
209
In a typical use of the EEG for diagnostics of sleep disorder, the features captured
from several hours of sleep EEG are compared to the features of standardized cases
of normal and abnormal cases. The standardized data file is often called a score file.
The comparison of patient feature matrices to the standard score file provides a platform for automated sleep pattern recognition. Ideally, the score system provides the
tool needed for automated identification of sleep disorders.
10.5.3 BRAIN TUMOR
The EEG can also indicate the presence of brain tumors. Both malignant and benign
masses in the brain can be the cause of epileptic episodes. In most cases, the presence of a tumor will reveal a focal source in the spatial EEG recordings. The tumor
can be regarded as an intermittent dipole, which can be located by reverse solution to
the spatial EEG recordings. The tumor will cause the greatest disturbances closest
to the tumor and will thus be identified by the electrode placement. Due to the relatively inexpensive nature of EEG recording, they are used as the initial examination
of patients suspected of having a brain tumor. The next step in the detection of the
brain tumor will be an MRI or a positron emission tomography (PET) session; both
techniques will be covered in Chapters 15 and 17, respectively.
10.5.4 OTHER DISEASES
Another common use of EEG is the diagnosis of meningitis. Meningitis is an infection
of the membranes that surround the brain, which may sometime cause inflammation
of the brain itself. Meningitis will typically result in capricious bursts of electric potentials at high frequency from randomized locations in the cortex that are reflected in the
EEG. With an infection of the meninges, which surrounds the cortex, a disturbance
of the depolarization of the gray matter neurons can be expected. The result is usually
wave trains of 1–1.5 Hz. The meningitis provokes the cortex, but not in one place only.
The infection-excited wave trains may also randomly shift in the spatial recordings.
Parkinson’s disease is the process of diminishing neural activity due to the fact
that nerve cells are consistently dying. This is an irreversible process in most cases,
but when diagnosed in an early stage, there is medication that can slow the process
down. The EEG of a Parkinson’s disease patient resembles that of a toddler or a
young child.
10.6 EEG FOR ASSESSMENT OF ANESTHESIA
During anesthesia, drugs are administered that are specifically aimed to depress
nerve cell activity. The effects of anesthetic and analgesic drugs result in specific
unusual patterns that can be observed in the EEG. Another cause for the slowing of
EEG is a lowered oxygen content of the blood (hypoxia) or a lowered carbon dioxide concentration (hypocapnia). A severe increase in carbon dioxide concentration
(hypercapnia) will cause a decrease in the EEG spectrum as well, while a small
increase in the carbon dioxide content can result in an increase in the spectral content of the EEG.
209
In a typical use of the EEG for diagnostics of sleep disorder, the features captured
from several hours of sleep EEG are compared to the features of standardized cases
of normal and abnormal cases. The standardized data file is often called a score file.
The comparison of patient feature matrices to the standard score file provides a platform for automated sleep pattern recognition. Ideally, the score system provides the
tool needed for automated identification of sleep disorders.
10.5.3 BRAIN TUMOR
The EEG can also indicate the presence of brain tumors. Both malignant and benign
masses in the brain can be the cause of epileptic episodes. In most cases, the presence of a tumor will reveal a focal source in the spatial EEG recordings. The tumor
can be regarded as an intermittent dipole, which can be located by reverse solution to
the spatial EEG recordings. The tumor will cause the greatest disturbances closest
to the tumor and will thus be identified by the electrode placement. Due to the relatively inexpensive nature of EEG recording, they are used as the initial examination
of patients suspected of having a brain tumor. The next step in the detection of the
brain tumor will be an MRI or a positron emission tomography (PET) session; both
techniques will be covered in Chapters 15 and 17, respectively.
10.5.4 OTHER DISEASES
Another common use of EEG is the diagnosis of meningitis. Meningitis is an infection
of the membranes that surround the brain, which may sometime cause inflammation
of the brain itself. Meningitis will typically result in capricious bursts of electric potentials at high frequency from randomized locations in the cortex that are reflected in the
EEG. With an infection of the meninges, which surrounds the cortex, a disturbance
of the depolarization of the gray matter neurons can be expected. The result is usually
wave trains of 1–1.5 Hz. The meningitis provokes the cortex, but not in one place only.
The infection-excited wave trains may also randomly shift in the spatial recordings.
Parkinson’s disease is the process of diminishing neural activity due to the fact
that nerve cells are consistently dying. This is an irreversible process in most cases,
but when diagnosed in an early stage, there is medication that can slow the process
down. The EEG of a Parkinson’s disease patient resembles that of a toddler or a
young child.
10.6 EEG FOR ASSESSMENT OF ANESTHESIA
During anesthesia, drugs are administered that are specifically aimed to depress
nerve cell activity. The effects of anesthetic and analgesic drugs result in specific
unusual patterns that can be observed in the EEG. Another cause for the slowing of
EEG is a lowered oxygen content of the blood (hypoxia) or a lowered carbon dioxide concentration (hypocapnia). A severe increase in carbon dioxide concentration
(hypercapnia) will cause a decrease in the EEG spectrum as well, while a small
increase in the carbon dioxide content can result in an increase in the spectral content of the EEG.