B, Beta rhythm consists of low-voltage, irregular >13-Hz activity overlying the frontal lobe. Because alpha activity reflects an anxiety-free state, it represents an important parameter in “alpha training,” biofeedback, and other behavior modification techniques.įIGURE 10-2 A, Alpha rhythm consists of regular 8–13-Hz activity overlying the occipital lobe. Preoccupations, concerns, or anxiety eliminate alpha activity. When people undergoing an EEG merely fix their gaze on a clock or add two single-digit numbers, faster rhythms replace alpha activity. It is prominent when individuals are relaxed with their eyes closed, but disappears if they open their eyes, concentrate, or are apprehensive. Neurologists refer to this pattern as the posterior dominant rhythm. The normal background rhythm in an awake adult consists of waves of activity in the alpha range of 8–13 cycles per second (Hertz ) detectable mostly over the occipital region ( Fig. They judge all these features in relation to whether the patient is awake, asleep, unresponsive, or having observable seizure activity. EEG readers accord special attention to unusually pointed single discharges, called sharp waves or spikes, and abnormal patterns, especially if they occur in paroxysms. Although approaches vary, most readers then determine the EEG’s background or dominant rhythm (see later), organization, and symmetry. They also determine the display of the electrodes (the montage) and note the time scale, which is determined by vertical lines on the EEG paper or displayed as 1-second horizontal bars.
TABLE 10-1 Common Electroencephalogram Rhythms ActivityĮEG readers first ascertain the patient’s age and level of consciousness. The P g electrodes attach to nasopharyngeal leads and the A electrodes, the ears (aural leads). Odd-numbered ones are on the left, and even-numbered ones on the right. FIGURE 10-1 In the standard array of scalp electrodes, most are named for the underlying cerebral region (e.g., frontal, temporal, central, parietal, and occipital).
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