Increase of theta/gamma ratio is associated with memory impairment

• Published in: Clinical neurophysiology Vol. 120; no. 2; pp. 295 - 303
• Main Authors: Moretti, D.V., Fracassi, C., Pievani, M., Geroldi, C., Binetti, G., Zanetti, O., Sosta, K., Rossini, P.M., Frisoni, G.B.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ireland Ltd 01.02.2009; Elsevier
• Subjects: Aged; Analysis of Variance; Biological and medical sciences; Brain - physiopathology; Brain Mapping; Cognitive tests; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Electrodiagnosis. Electric activity recording; Electroencephalography; Female; Gamma rhythm; Humans; Investigative techniques, diagnostic techniques (general aspects); Linear coherence; Magnetic Resonance Imaging; Male; Medical sciences; Memory Disorders - pathology; Memory Disorders - physiopathology; Middle Aged; Mild cognitive impairment; Nervous system; Neurology; Spectrum Analysis; Theta rhythm; Linear coherence; Electroencephalography; Theta rhythm; Cognitive tests; Mild cognitive impairment; Gamma rhythm; Modification; Memory disorder; Cognitive disorder; Memory; Central nervous system; Electrophysiology; Encephalon; Degenerative disease; Coupling; Human; Nervous system diseases; Regression analysis; Nuclear magnetic resonance imaging; Cerebral disorder; Temporal frequency; Correlation analysis; Central nervous system disease; Coherence; mild cognitive impairment; Performance
• ISSN: 1388-2457; 1872-8952; 1872-8952
• DOI: 10.1016/j.clinph.2008.11.012

In this study the theta/gamma ratio was investigated as early marker of cognitive decline. Forty-nine subjects with mild cognitive impairment (MCI) underwent EEG recording and MRI scan. The theta/gamma ratio of the relative power at the peak frequency was computed. Based on the tertiles values of the ratio, three groups with increasing values of theta/gamma ratio were obtained. The groups were characterized by the performance on cognitive tests. Changes in functional brain connectivity, as expressed by interhemisperic and intrahemispheric EEG linear coherence in the groups were also evaluated. Increase in theta/gamma ratio was associated with impairment in memory tests. This relationship was confirmed by correlation and multiple regression analysis. An independent association was found between theta/gamma ratio and alpha3/alpha2 power ratio. Coherence analysis showed modifications of interhemispheric functional coupling on temporal regions on slow frequencies. Theta/gamma ratio of relative power at peak frequency is significantly associated to memory decline. It could be a useful tool in detecting MCI subjects which are at major risk to develop Alzheimer’s disease (AD) or other dementias. A global modulation of brain rhythms could be driven by the pathological alterations of theta/gamma ratio.