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When attentive to external stimulus or thinking hard about anything, the a wave is replaced by (3 rhythm. They are seen during tension or CNS activation. They are frequently recorded from the parietal and frontal region. They have lower voltage than alpha waves. Frequencies of alpha rhythm are also decreased in conditions like low blood glucose level, low body temperature, low level of adrenal glucocorticoids and high arterial partial pressure of CO 2.If there is a consistent difference of 1 Hz or more in alpha frequency between two cerebral hemispheres, the side of lower frequency is likely to be involved in pathological process.īeta waves have frequency more than 13 cycles per second and may be as high as 25Hz. The mean peak alpha frequency is 10.2 Hz and decreases in old age due to decreased cerebral perfusion leading to decreased cerebral metabolic rate. They are fairly regular pattern of waves at a frequency of 8 – 13 / sec and an amplitude of 50 – 100 pV.
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They disappear entirely during deep sleep. They disappear on opening the eyes and on attentive mind. They are most marked in the parietooccipital area of the scalp when the person is awake, quite and resting with eyes closed. Alpha waves are the most prominent component of the EEG. The main types of EEG waves are alpha, beta, theta and delta waves.