Nowlis and Kamiya ( 81) and Brown ( 82) associated alpha rhythm enhancement (on a вЂњvoluntaryвЂќ basis) with a pleasant mood. This work was presumably prompted by the observation of well-modulated alpha during meditation practiced by yogis ( 78, 79) or zen buddhists (Hirai, 1968, and Kasamatsu and Hirai, 1966, both articles cited in Ref. Voluntary control of the alpha rhythm and the use of alpha feedback methods have been widely discussed topics since the late 1960s. With a nonchalant approach, there is usually no alpha blocking. Other factors may also be at work: even simple arithmetic may cause alpha blocking if the subject shows great motivation trying to please the examiner. A possible explanation for the discrepancy lies in the difficulty of the task: the arithmetical problems given to BergerвЂ™s two teenage children, Klaus and Ilse, were more challenging. On the other hand, Berger ( 40, 45, 46, 47 and 48) showed fine examples of arithmeticinduced alpha blocking. In a study done in 1280 patients (598 with normal EEG tracings, 682 with various degrees of EEG abnormality), alpha suppression or attenuation with calculation (serial sevens) was noted in only 21 (1.6%) of the patients. Indeed, the blocking or attenuating effect of mental arithmetic on the posterior alpha rhythm may not be present in most cases ( 44). It is the goal of this chapter to define and describe these recognizable elements, with attention to their clinical implications and their significance for our understanding of underlying cerebral physiology.ДЄlpha attenuation due to auditory, tactile, and other somatosensory stimuli or heightened mental activity (such as solving difficult arithmetical problems) is usually less pronounced than the blocking effect with eye opening. Having said that, decades of EEG study, beginning with BergerвЂ™s early fundamental descriptions and continuing now with advanced power spectral analyses, have shown us that there are certain basic recognizable patterns, seen at least some of the time in almost all healthy individuals, that together constitute what we would consider to be representative of a normal EEG. Such is the nature of human EEG, and this must be kept in mind in the clinical interpretation of tracings. In other words, there is no single rhythm, feature, or characteristic of an EEG that must be present to make it normal (except, perhaps, reactivity), and, indeed, no combination of any such findings either. Many clinical elec-troencephalographers would define normality on an EEG as being simply the absence of identifiable abnormalities. A chapter on the normal EEG is actually more difficult to organize than it might seem.

Normal eeg