Elsevier

Neuroscience

Volume 150, Issue 2, 5 December 2007, Pages 346-356
Neuroscience

Clinical neuroscience
Working memory load–related electroencephalographic parameters can differentiate progressive from stable mild cognitive impairment

https://doi.org/10.1016/j.neuroscience.2007.09.009Get rights and content

Abstract

Recent studies described several changes of endogenous event-related potentials (ERP) and brain rhythm synchronization during memory activation in patients with Alzheimer’s disease (AD). To examine whether memory-related EEG parameters may predict cognitive decline in mild cognitive impairment (MCI), we assessed P200 and N200 latencies as well as beta event-related synchronization (ERS) in 16 elderly controls (EC), 29 MCI cases and 10 patients with AD during the successful performance of a pure attentional detection task as compared with a highly working memory demanding two-back task. At 1 year follow-up, 16 MCI patients showed progressive cognitive decline (PMCI) and 13 remained stable (SMCI). Both P200 and N200 latencies in the two-back task were longer in PMCI and AD cases compared with EC and SMCI cases. During the interval 1000 ms to 1700 ms after stimulus, beta ERS at parietal electrodes was of lower amplitude in PMCI and AD compared with EC and SMCI cases. Univariate models showed that P200, N200 and log% beta values were significantly related to the SMCI/PMCI distinction with areas under the receiver operating characteristic curve of 0.93, 0.78 and 0.72, respectively. The combination of all three EEG hallmarks was the stronger predictor of MCI deterioration with 90% of correctly classified MCI cases. Our data reveal that PMCI and clinically overt AD share the same pattern of working memory-related EEG activation characterized by increased P200–N200 latencies and decreased beta ERS. They also show that P200 latency during the two-back task may be a simple and promising EEG marker of rapid cognitive decline in MCI.

Section snippets

Inclusion procedure and follow-up

The sample included 16 EC, 29 MCI subjects and 10 AD patients. ECs were recruited through the University of Geneva. All individuals were screened with the Mini Mental State Examination (MMSE) (Folstein et al., 1975), Hospital Anxiety and Depression Scale (HAD, Zigmond and Snaith, 1983) and Lawton’s Instrumental Activities of Daily Living (IADL, Barberger-Gateau et al., 1992). Depressive co-morbidity was excluded on the basis of a HAD score consistently less than 8. Subjects with MMSE scores of

Clinical data

One year after baseline assessment (range 12.0±0.4 months), 16 (55%) of the original MCI cases demonstrated significant cognitive decline and constituted the PMCI group. Among these cases only three converted into AD. The remaining 13 cases (45%) showed no change in cognitive function, except an executive motor slowing indicated by the Trail Making test A (78.60±31.95 s vs 96.08±33.37 s; P<0.01). This difference was not clinically significant with respect to normative thresholds and is

Discussion

Strengths of the present study include its longitudinal design, confirmation of the MCI diagnosis by two independent clinicians blind to the study purposes, control for medications which influence EEG dynamics and use of three event-related EEG measurements known to be associated with working memory activation. Our data reveal that PMCI and clinically overt AD share the same pattern of working memory–related EEG activation characterized by increased P200–N200 latencies and decreased beta ERS

Acknowledgments

This project was funded by the Swiss National Foundation for Scientific Research, grant 3100A0/103770/1; the Research and Development Hospital, grant 02-1-122; as well as by unrestricted grants from the Novartis Foundation, Ernst and Lucie Schmidheiny Foundation, and Stiftung für Klinische Neuropsychiatrische Forschung.

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