3.1. Phantom Spike Wave (Six Per Second Spike Wave Complex)
This pattern looks like a miniature version of the typical three per second spike wave of typical absence. The spike component is often unimpressive (hence, the "phantom spike" designation). Although it may be diffuse, at times the distribution of this phenomenon and the state in which it occurs allow discrimination of two forms. It occurs in waking, at relatively higher amplitude and the anterior head regions in male subjects (Fig. 28), and, in female subjects, is typically occipital, of lower amplitude, and occurs in drowsiness. The discharge usually lasts 1 to 2 s, but may persist longer. It is usually symmetrical, but may have a lateral predominance. This pattern is present in adolescence and adulthood. Unlike more pathological spike wave patterns, it tends to disappear as sleep deepens. Although here described as a normal variant, the status of phantom spike wave as denoting increased risk of seizure has been controversial, particularly the anterior/frontal form, which some authors consider more likely to be associated with other epileptiform findings and with epileptic seizures.
3.2. Fourteen- and 6-Hz Positive Spikes (Fig. 29)
This benign pattern is first observed in early childhood, achieves maximum frequency in the adolescent age group, and wanes thereafter. It is observed in drowsiness and sleep, has a broad field, but is usually maximum in the posterior temporal area. At times, the 14-Hz or the 6-Hz component may predominate. The 14-Hz component may be observed more frequently in middle childhood or adolescence, the 6-Hz pattern in younger children and young adults. The discharge may last 1 to 2 s. It often occurs independently on both sides. Because the amplitude is low, it is best observed with referential montages, which, in general, use longer interelectrode distances.
This is a rare pattern. It is observed in adolescents and adults. It occurs in drowsiness, and, similar to other benign patterns, disappears as sleep supervenes. It may occur bilaterally or independently. It begins with rhythmic sharply contoured, often notched or flat-topped theta waves in the mid-temporal area. The amplitude and field increase, but there is no evolution in frequency or of waveform. These last features help distinguish this pattern from true seizure. This pattern is no longer thought to denote increased risk of seizure or epilepsy.
3.4. Alpha Variant Patterns 3.4.1. Slow Alpha Variant
This is most likely the result of the superimposition of two alpha rhythms producing the sudden appearance of a notched posterior rhythm at half the previous frequency. Similar to the individual's usual alpha frequency, it is blocked by eye opening. This change may occur in trains during normal alpha activity. It may be more likely to occur in drowsiness.
3.4.2. Fast Alpha Variant
This typically occurs on first eye closure, when a beta-range activity occurs in the posterior regions, which attenuates with eye opening. This is usually replaced within a second or two by the individual's usual alpha frequency. This fast occipital activity has been described as the "squeak" phenomenon. Both the slow and fast alpha variants are normal physiological phenomena.
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