The alertness level of 143 patients with dementia was investigated. The patients were examined clinically and electroencephalographically, and the results were compared with 21 healthy volunteers. Regional brain syndromes were determined clinically. For the assessment of the EEG, a method was employed that distinguishes alertness-related slow wave activity from abnormal slow activity. The shifts of the EEG power were monitored during the 5-min examination. The short-term variations were considered to be caused by changes in alertness, whereas the basal level was supposed to reflect the EEG abnormality. It was found that a decrease in alertness occurred more often in the demented patients than in the controls. The intensity of this decrease was proportional to the degree of the dementia. The alertness disturbance was found to be particularly associated with the parietal brain syndrome.
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