Coherence Characteristics of Gamma-band EEG during rest and cognitive task in MCI and AD

The aim of this study is to investigate whether EEG coherence during different functional states facilitates the detection of AD-related EEG changes; and which brain regions these changes were. The EEGs in both rest and performing the cognitive task states of 3 groups was recorded for coherence measure. The 3 groups are the mild cognitive impairment (MCI) group, Alzheimer's disease(AD) and the healthy control group. In rest state, coherence value of EEG for AD group was lower than that in other two groups in channel pairs of Fp2-T4, F4-C4 (P<0.01) and F3-C3, Fp1-T3, P3-O1 (P<0.05). There was no significant difference between the MCI and control. In cognitive performing state (counting the target number), coherence of EEGs in all channel connections for AD group were lower compared with MCI and control group. Furthermore, in Fp2-T4 (prefrontal-temporal) and F4-C4(frontal-central) pairs, MCI showed significant lower coherence than that in control. The conclusion of this study was that the coherence of EEG would seem to be a useful and more sensitive indicator for cognitive impairment in cognitive performing state than that in rest, and AD patient showed coherence abnormal changes in more regions in this state. The abnormal localization also suggested the AD-related cognitive impairment maybe commence with frontal activity abnormality and then spread to the other brain regions.