A quantitative and correlative study of the dominant occipital rhythm in Senile dementia of the Alzheimer's type

Parameters derived from power spectral analysis of the electroencephalogram (EEC) were examined in normal aging and Senile Dementia of the Alzheimer's Type (SDAT) and correlated with neuropsychologic measures of cognitive function. The parameters chosen for study focussed on quantifying aspects of the Dominant Occipital Rhythm (DOR) as it changed across time and across several stimulus conditions (eyes closed, eyes open, and listening to speech). In contrast with most prior spectral analysis studies which used fixed frequency bands, in this study algorithms to locate and measure DOR frequency, amplitude, bandwidth, and sharpness characteristics were applied to individual data epochs. Total 0.25-32.00 Hz spectrum power, weighted mean frequency, and power in the frequency bands adjacent to DOR were also measured. Data was collected from a group of 11 normally aged subjects (5 males, 6 females, mean age 64.7 years) and a group of 11 SDAT patients (2 males and 9 females, mean age 72.7 years). The SDAT patients demonstrated lower DOR frequency and weighted mean frequency than normals in each stimulus condition. On amplitude variance measures, the DOR of SDATs was seen to be less reactive to condition change and less modulated within conditions than that of normals. A number of EEC measures, including some of the variance measures, correlated with psychologic measures by rank. Thus, spectral parameter variance measures, particularly those related to DOR amplitude, are sensitive to moderate SDAT and are worthy of further investigation.