Cognitive decline unlike normal aging is associated with alterations of EEG temporo-spatial characteristics

Abstract The diagnosis of beginning dementia is based mainly on neuropsychological testing. Several measures of EEG spectral composition, coherence and complexity (correlation dimension) have been shown to correspond to cognitive function. Only a few studies have evaluated EEG changes in normal aging, and no quantitative study has addressed changes in EEG during cognitive tasks in demented elderly. In this study the quantitative descriptors of EEGs from 31 demented or cognitively impaired elderly persons, 30 healthy elderly (mean age 69 years) and 35 young controls (mean age 31 years) were compared. The EEGs were recorded during two resting conditions (eyes closed and eyes opened) and two tasks (mental arithmetics and a lexical decision). The goal of the study was to evaluate which temporal and spatial EEG descriptors change with cognitive decline and with normal aging, respectively. Cognitive categories (unimpaired, impaired, demented) were based on Structured Interview for the Diagnosis of Dementia of Alzheimer Type (SIDAM) scores. The EEGs were analysed using adaptive segmentation of continuous EEG, which quantifies the succession of distinct stable topographic voltage patterns (EEG microstates). The main findings were a significant increase in the number of ultra-short EEG microstates and, independently, a reduction in the average duration of EEG microstates in the cognitively impaired and demented patients. In addition, cognitive impairment was associated with a reduction or loss of EEG reactivity normally observed when the resting states with closed and with opened eyes are compared. No alterations in temporal or spatial EEG descriptors were found in normal aging. Cognitive tasks did not add to information already obtained during the resting states. The reduction in EEG microstate duration correlated with loss of cognitive function. Temporo-spatial analysis of EEG therefore is a useful indicator of cortical dysfunction in dementia, correlating with the degree of cognitive impairment. Normal aging seems not to be accompanied by changes in temporo-spatial EEG patterns. The data suggest that fragmentation of the electrophysiological processes underlies cognitive dysfunction in Alzheimer’s disease.

[1]  S. Folstein,et al.  "Mini-mental state". A practical method for grading the cognitive state of patients for the clinician. , 1975, Journal of psychiatric research.

[2]  M. Bryden.  Measuring handedness with questionnaires , 1977, Neuropsychologia.

[3]  F H Duffy,et al.  Age‐related differences in brain electrical activity of healthy subjects , 1984, Annals of neurology.

[4]  J. Yesavage,et al.  Geriatric Depression Scale (GDS): Recent evidence and development of a shorter version. , 1986 .

[5]  D Lehmann,et al.  EEG alpha map series: brain micro-states by space-oriented adaptive segmentation. , 1987, Electroencephalography and clinical neurophysiology.

[6]  F. D. Silva.  Neural mechanisms underlying brain waves: from neural membranes to networks. , 1991 .

[7]  G. Barnes,et al.  Pursuit of intermittently illuminated moving targets in the human. , 1992, The Journal of physiology.

[8]  D O Walter,et al.  Changes in brain functional connectivity in Alzheimer-type and multi-infarct dementia. , 1992, Brain : a journal of neurology.

[9]  T Dierks,et al.  Segmentation of the spontaneous EEG in dementia of the Alzheimer type. , 1993, Neuropsychobiology.

[10]  D. Lehmann,et al.  Adaptive segmentation of spontaneous EEG map series into spatially defined microstates. , 1993, International journal of psychophysiology : official journal of the International Organization of Psychophysiology.

[11]  V B Mountcastle.  Temporal Order Determinants in a Somesthetic Frequency Discrimination: Sequential Order Coding , 1993, Annals of the New York Academy of Sciences.

[12]  D Lehmann,et al.  Data-determined window size and space-oriented segmentation of spontaneous EEG map series. , 1993, Electroencephalography and clinical neurophysiology.

[13]  T Dierks,et al.  Age-related changes of spontaneous EEG described by equivalent dipoles. , 1993, International journal of psychophysiology : official journal of the International Organization of Psychophysiology.

[14]  Curt von Euler,et al.  Temporal Information Processing in the Nervous System: Special Reference to Dyslexia and Dysphasia. Conference proceedings. New York City, New York, September 12-15, 1992. , 1993, Annals of the New York Academy of Sciences.

[15]  R Llinás,et al.  Is Dyslexia a Dyschronia? , 1993, Annals of the New York Academy of Sciences.

[16]  H. Semlitsch,et al.  Discrimination between demented patients and normals based on topographic EEG slow wave activity: comparison between z statistics, discriminant analysis and artificial neural network classifiers. , 1994, Electroencephalography and clinical neurophysiology.

[17]  J. Calabrese,et al.  Quantification of occipital EEG changes in Alzheimer's disease utilizing a new metric: The fractal dimension , 1994, Biological Psychiatry.

[18]  K. Coburn,et al.  EEG-based, neural-net predictive classification of Alzheimer's disease versus control subjects is augmented by non-linear EEG measures. , 1994, Electroencephalography and clinical neurophysiology.

[19]  Kaisu Le Roc'h.  EEG coherence in Alzheimer disease, by Besthorn et al. , 1994 .

[20]  J. Cummings,et al.  Vascular subcortical dementias: clinical aspects. , 1994, Dementia.

[21]  Michael Recce,et al.  A model of hippocampal function , 1994, Neural Networks.

[22]  H Sattel,et al.  Parameters of EEG dimensional complexity in Alzheimer's disease. , 1995, Electroencephalography and clinical neurophysiology.

[23]  A. Leuchter,et al.  Relationships between EEG Coherence and Neuropsychological Tests in Dementia , 1995, Clinical EEG.

[24]  F Angeleri,et al.  EEG spectral analysis in vascular and Alzheimer dementia. , 1995, Electroencephalography and clinical neurophysiology.

[25]  M. Hasselmo,et al.  Cholinergic modulation of cortical oscillatory dynamics. , 1995, Journal of neurophysiology.

[26]  G. Buzsáki,et al.  Temporal structure in spatially organized neuronal ensembles: a role for interneuronal networks , 1995, Current Opinion in Neurobiology.

[27]  J E Lisman,et al.  Storage of 7 +/- 2 short-term memories in oscillatory subcycles , 1995, Science.

[28]  C. Morawetz,et al.  Dementia and depression: Co-distribution and risk factors in a geriatric in- and outpatient sample , 1996, European Psychiatry.

[29]  Werner Strik,et al.  Increased duration and altered topography of EEG microstates during cognitive tasks in chronic schizophrenia , 1997, Psychiatry Research.