Regional correlations between the EEG and oxygen metabolism in dementia of Alzheimer's type

Correlation between cortical theta activity and hippocampal volumes in health, mild cognitive impairment, and mild dementia

Cognitive decline is known to be associated with both increased theta power over frontal regions and hippocampal atrophy. The aim of this study was to reveal the relation between these parameters in groups with mild dementia, mild cognitive impairment, and healthy control subjects. The authors examined a preliminary randomly selected sample of 39 right-handed subjects joining the Leipzig Longitudinal Study of the Aged, consisting of 17 normal elderly subjects, 12 patients with mild cognitive impairment, and 10 patients with mild dementia assessed by Clinical Dementia Rating. All subjects were between 75 and 85 years old (mean age, 78 years; standard deviation, 2.78 years) and underwent EEG and brain MRI. Mean spectral power densities were calculated, and hippocampal body volume was measured. Significant negative linear correlations between theta power over frontal regions and hippocampal volumes were found. The results support the assumption about a relationship between hippocampal atrophy and theta power, and may be helpful for a better understanding of the course of Alzheimer's disease.

Spatial pattern of cerebral glucose metabolism (PET) correlates with localization of intracerebral EEG-generators in Alzheimer's disease

BACKGROUND

Since the measurement of human cerebral glucose metabolism (GluM) by positron emission tomography (PET) and that of human cerebral electrical activity by EEG reflect synaptic activity, both methods should be related in their cerebral spatial distribution. Healthy subjects do indeed demonstrate similar metabolic and neuroelectric spatial patterns.

OBJECTIVE

The aim of the study was to show that this similarity of GluM and EEG spatial patterns holds true in a population with a high variability of glucose metabolism.

METHODS

We investigated healthy control subjects and patients with varying degrees of cognitive dysfunction and varying GluM patterns by applying [18F]FDG PET and EEG.

RESULTS

We demonstrated that the localization of intracerebral generators of EEG correlates with spatial indices of GluM.

CONCLUSION

These results indicates that EEG provides similar spatial information about brain function as GluM-PET. Since EEG is a non-invasive technique, which is more widely available and can be repeated more often than PET, this may have important implications both for neuropsychiatric research and for clinical diagnosis. However, further studies are required to determine whether equivalent EEG dipole generators can yield a diagnostic specificity and sensitivity similar to that of GluM-PET.

Clinical neurophysiology using electroencephalography in geriatric psychiatry: neurobiologic implications and clinical utility

Electroencephalography (EEG) offers a unique contribution to the armamentarium of imaging technologies used in the evaluation of brain function. The primary clinical application of EEG is in the diagnosis of delirium, dementia, and epilepsy, which are frequently encountered in the practice of geropsychiatry. This review summarizes the principles behind generation of the EEG signal, its strengths and limitations as a technology, clinical indications for performing an EEG, the principles underlying quantitative EEG (QEEG), and how QEEG is allowing us to probe brain function and connectivity in new ways.

Decrease of non-linear structure in the EEG of Alzheimer patients compared to healthy controls

OBJECTIVE

Non-linear EEG analysis can provide information about the functioning of neural networks that cannot be obtained with linear analysis. The correlation dimension (D2) is considered to be a reflection of the complexity of the cortical dynamics underlying the EEG signal. The presence of non-linear dynamics can be determined by comparing the D2 calculated from original EEG data with the D2 from phase-randomized surrogate data.

METHODS

In a prospective study, we used this method in order to investigate non-linear structure in the EEG of Alzheimer patients and controls. Twenty-four patients (mean age 75.6 years) with 'probable Alzheimer's disease' (NINCDS-ADRDA criteria) and 22 controls (mean age 70.3 years) were examined. D2 was calculated from original and surrogate data at 16 electrodes and in three conditions: with eyes open, eyes closed and during mental arithmetic.

RESULTS

D2 was significantly lower in the Alzheimer patients compared to controls (P = 0.023). The difference between original and surrogate data was significant in both groups, implicating that non-linear dynamics play a role in the D2 value. Moreover, this difference between original and surrogate data was smaller in the patient group. D2 increased with activation, but not significantly more in controls than in patients.

CONCLUSIONS

In conclusion, we found decreased dimensional complexity in the EEG of Alzheimer patients. This decrease seems to be attributable at least partially to different non-linear EEG dynamics. Because of this, non-linear EEG analysis could be a useful tool to increase our insight into brain dysfunction in Alzheimer's disease.