<h4><b>Minimum Technical Requirements for Performing Clinical
Electroencephalography</b></h4><p>According to the <b>American Clinical Neurophysiological Society</b>, to find the distribution of EEG activity, it is necessary to record simultaneously
from as many regions of the scalp as possible. When too few channels are used
simultaneously, the chances of interpretive errors increase, and, conversely, when more
channels are utilized, the likelihood of such errors decreases. This is particularly true for
transient activity.
Sixteen channels of simultaneous recording are now considered the minimum number
required to show the areas producing most normal and abnormal EEG patterns.
Additional channels can be used for monitoring other physiologic activities (such as ocular movement, glossokinetc movement, or respiration.&nbsp;<br></p><p>Recording electrodes should be free of inherent noise and drift.&nbsp;To decrease noise, electrodes must be kept clean, with appropriate precautions taken
after recording from patients with contagious diseases.<br></p><p>All 21 electrodes and placements recommended by the International Federation of
Clinical Neurophysiology (IFCN; Jasper HH, 1958, 1983) should be used. The 10-20
System is the only one officially recommended by the IFCN. It is the most commonly
used existing system, and it should be used universally.&nbsp;An adequate number of electrodes is essential to ensure that EEG activity having a
small area of representation on the scalp is recorded and to analyze accurately the
distribution of more diffuse activity. A smaller number of electrodes may be appropriate
for special circumstances, but is not considered comprehensive.</p><p>A grounding electrode always should be used. The ground electrode on the patient must
be connected only to the appropriate jack of the input jackbox, and never to the
equipment chassis or other earth ground.<br></p><p>Interelectrode impedances should be checked as a routine prerecording procedure.
Ordinarily, electrode impedance should not exceed 15000 Ohms (15 KOhms.)<br></p><p>For standard recordings, the low-frequency filter should be no higher than 1 Hz (—
3 dB) corresponding to a time constant of at least 0.16 s. The high-frequency filter should
be no lower than 70 Hz (-3 dB). Note, however, that to display frequencies as high as 70
Hz, a computer monitor would need a horizontal resolution of at least 1400 pixels in the
data display area.&nbsp;A low-frequency filter setting higher than 1 Hz should not be used routinely to
attenuate slow-wave artifacts in the record. Vital information may be lost when
pathologic activity in the delta range is present. Similarly, a setting lower than 70 Hz for
the high-frequency filters can distort or attenuate spikes and other pathologic discharges
into unrecognizable forms and can cause muscle artifact to resemble spikes. Production
of a record with lost or inaccurate information is poor medical practice.
It must be emphasized, however, that judicious use of the low- or high-frequency
filters—with appropriate annotation on the record—can emphasize or clarify certain
types of patterns in the record. These filter controls, therefore, should be used in analysis.&nbsp;<br></p><p>The baseline record should contain at least 20 min of technically satisfactory
recording (10 minutes eyes open and 10 minutes eyes closed is standard in the USA). Longer recordings are often more informative. Although the possibility of
reformatting digital EEG allows the entire recording to be performed in a single montage,
this is not acceptable practice. Observing only one montage may prevent recognition of
poor connections in electrodes that happen not to be included, and also prevent
appreciation of subtle abnormalities that require special technical maneuvers (such as
placement of additional electrodes.)
The EEG is a short sample in time from the patient’s life. Within reasonable limits, the
longer the recording, the better the chance of recording an abnormality or abnormalities
demonstrating the variability of these. Experience in many centers shows that a very
minimum of 20 min of artifact-free recording is necessary to assess baseline waking EEG
activity.&nbsp;<br></p>