Electroencephalogram
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short burst of frequencies between 12 and 14 Hz also appear in the EEG. These
bursts are called spindles. The presence of beta (and to some degree, alpha) during sleep describes why a major application of EEG is the diagnostics of different
types of sleep disorders. For instance, a healthy night sleep must contain a rather
long REM period that is typically detected by the occurrence of beta waves. The
absence or the short duration of beta (and other similar waves) often indicates an
abnormal sleep.
Due to the age dependency of the EEG signal, this signal has significant applications in the diagnostics of age-related disorders. It is known that during childhood
the dominant EEG frequencies increase with age. A newborn baby has frequencies
ranging from 0.5 to 2 Hz. At the end of the second year, the EEG already displays
short stretches of alpha waves. At the age of 14, however, the brain wave pattern is
virtually undistinguishable from an adult. The presence or absence of certain frequencies in a person belonging to a particular age group is an indication of abnormality of the brain activities.
In general, the measure of conciseness can be derived from the frequency components of the EEG signal, i.e., as higher frequencies are detected, the patient is more
alert and mentally occupied. In addition to the increase in frequency with increased
activity, the neural activity will show less coherence (i.e., more chaotic behavior)
with an increase in the alertness. This is due to the fact that in an alert brain, each
neuron acts more and more independent from its neighbors and desynchronization
becomes more prevalent. The measurement of general electric activity of the brain
is called spontaneous activity, which represents the apparent chaotic brain activity.
There are two internationally accepted methods of testing the brain activity that
are commonly applied in clinical measurements. These two methods are EP recordings and ERP recordings. These two methods will be explained next.
10.4 EVOKED POTENTIALS
EPs are the EEG signals generated under external stimuli such as auditory input
or visual input. EPs are typically used to diagnose the sensory properties and also
the motor pathways within the specialized sections of the CNS. The different types
of EP measurements form three classes of measurements: auditory evoked potentials (AEPs), somatosensory evoked potentials (SEPs), and visual evoked potentials
(VEPs). These methods of stimuli to perform diagnostic utilities are discussed next.
10.4.1 AUDITORY-EVOKED POTENTIALS
AEPs are used to check for hearing damage and the source of the damage, either
mechanical or neurological. During the course of AEP measurement, tones with
different frequencies are played on a headphone attached to the patient’s ears. While
the tones are played, the EEG signals are recorded and marked according to the
frequency of the tone. In the processing step, the correlation between the tone signal and the recorded EEG will determine the sensitivity of the CNS to the played
tone. More specifically, when the brain is not responding to a tone with a particular
frequency, the case can be diagnosed as pathological. The real problem observed in
203
short burst of frequencies between 12 and 14 Hz also appear in the EEG. These
bursts are called spindles. The presence of beta (and to some degree, alpha) during sleep describes why a major application of EEG is the diagnostics of different
types of sleep disorders. For instance, a healthy night sleep must contain a rather
long REM period that is typically detected by the occurrence of beta waves. The
absence or the short duration of beta (and other similar waves) often indicates an
abnormal sleep.
Due to the age dependency of the EEG signal, this signal has significant applications in the diagnostics of age-related disorders. It is known that during childhood
the dominant EEG frequencies increase with age. A newborn baby has frequencies
ranging from 0.5 to 2 Hz. At the end of the second year, the EEG already displays
short stretches of alpha waves. At the age of 14, however, the brain wave pattern is
virtually undistinguishable from an adult. The presence or absence of certain frequencies in a person belonging to a particular age group is an indication of abnormality of the brain activities.
In general, the measure of conciseness can be derived from the frequency components of the EEG signal, i.e., as higher frequencies are detected, the patient is more
alert and mentally occupied. In addition to the increase in frequency with increased
activity, the neural activity will show less coherence (i.e., more chaotic behavior)
with an increase in the alertness. This is due to the fact that in an alert brain, each
neuron acts more and more independent from its neighbors and desynchronization
becomes more prevalent. The measurement of general electric activity of the brain
is called spontaneous activity, which represents the apparent chaotic brain activity.
There are two internationally accepted methods of testing the brain activity that
are commonly applied in clinical measurements. These two methods are EP recordings and ERP recordings. These two methods will be explained next.
10.4 EVOKED POTENTIALS
EPs are the EEG signals generated under external stimuli such as auditory input
or visual input. EPs are typically used to diagnose the sensory properties and also
the motor pathways within the specialized sections of the CNS. The different types
of EP measurements form three classes of measurements: auditory evoked potentials (AEPs), somatosensory evoked potentials (SEPs), and visual evoked potentials
(VEPs). These methods of stimuli to perform diagnostic utilities are discussed next.
10.4.1 AUDITORY-EVOKED POTENTIALS
AEPs are used to check for hearing damage and the source of the damage, either
mechanical or neurological. During the course of AEP measurement, tones with
different frequencies are played on a headphone attached to the patient’s ears. While
the tones are played, the EEG signals are recorded and marked according to the
frequency of the tone. In the processing step, the correlation between the tone signal and the recorded EEG will determine the sensitivity of the CNS to the played
tone. More specifically, when the brain is not responding to a tone with a particular
frequency, the case can be diagnosed as pathological. The real problem observed in