Which findings on EEG are characteristic of dementia?

Updated: Oct 09, 2019
  • Author: Eli S Neiman, DO, FACN; Chief Editor: Selim R Benbadis, MD  more...
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In early dementia, the resting alpha frequency declines. Most authors agree that the lower limit of normal alpha frequency is 8 Hz (cycles per second). Medications can slow the posterior dominant rhythm; therefore, medication effect should always be excluded. In assessing the frequency of the alpha rhythm, alerting maneuvers are essential in order to ensure that the patient is in the best awake state and not drowsy. Computerized methods, such as EEG spectral analysis [2] , coherence, and complexity (ie, correlation dimension), have been demonstrated to correspond to cognitive function. [3]

Stevens et al recorded EEGs during 2 resting conditions (eyes closed and eyes opened) and 2 tasks (mental arithmetic and a lexical decision), with the aim of determining which temporal and spatial EEG descriptors change with cognitive decline and normal aging. [4] The EEGs were analyzed by using EEG microstates. The primary findings were a significant increase in the number of ultrashort EEG microstates and a reduction in the average duration of EEG microstates in cognitively impaired and demented patients.

Cognitive impairment was associated with a reduction or loss of EEG reactivity. [4] In contrast, no alterations in temporal or spatial EEG descriptors were found in normal aging. Cognitive tasks did not add to the information already obtained during the resting states. The reduction in EEG microstate duration correlated with loss of cognitive function.

Therefore, temporospatial analysis of the EEG record is a useful indicator of cortical dysfunction in dementia and correlates with the degree of cognitive impairment. Apparently, temporospatial analysis may be useful in distinguishing patients with dementia from those experiencing normal aging. Whether these data contribute significant additional information to the clinical data in evaluating dementia is unclear.

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