[Verbal fluency and EEG coherence in Alzheimer's disease]

EEG coherence of 16 derivations and a verbal fluency test were evaluated on 25 ambulatory patients suffering from Alzheimer's disease (age: 74 +/- 5.7). The aim of the study was to analyze coherence rate variations from different cortical areas in relation to the performance in the test. Coherence rates of each derivation with the other ones were calculated for four frequency bands from 0.5 to 13.5 Hz. Arithmetic averages of these rates were then calculated to obtain scalp averaged coherence rates. The patients were submitted to a verbal fluency test and divided into two groups according to their test score as compared to normative data: impaired (n = 10) and not impaired (n = 15). Results showed that averaged coherence rates of theta and alpha 1 frequency bands were significantly depressed in the impaired group in comparison with those of the not impaired group. Two cortical areas were concerned with this difference, the left temporo-occipital and frontal zones, in an independent way for the same subject. Moreover, we observed that the patients who where impaired in the verbal fluency test, also presented a significantly greater ancientness of the clinical symptoms as compared to the not impaired patients.