Increase of Theta/Gamma and Alpha3/Alpha2 Ratio is Associated with Amygdalo-Hippocampal Complex Atrophy

Abstract

We evaluated the association between amygdalo-hippocampal complex (AHC) atrophy and two electroencephalography (EEG) markers of cognitive decline: increase of theta/gamma and increase of alpha3/alpha2 relative power ratio. Seventy-nine subjects with mild cognitive impairment (MCI) underwent EEG recording and magnetic resonance imaging scan. Based on the tertiles values of decreasing AHC volume, three groups of AHC growing atrophy were obtained. The groups were characterized by the performance to cognitive tests and theta/gamma and alpha3/alpha2 relative power ratio. AHC atrophy is associated with memory deficits as well as with increase of theta/gamma and alpha3/alpha2 ratio. Moreover, when the amygdalar and hippocampal volume are separately considered within AHC, the increase of theta/gamma ratio is best associated with amygdalar atrophy whereas alpha3/alpha2 ratio is best associated with hippocampal atrophy. AHC atrophy is associated with memory deficits and EEG markers of cognitive decline. So far, these EEG markers could have a prospective value in differential diagnosis between patients with MCI who develop dementia and those who do not as well as between MCI patients who will develop Alzheimer's disease and those who develop non-Alzheimer's disease dementias. The alterations of the functional connections, inducing global network pathological changes, in the whole AHC could better explain MCI state.