Left Temporal Neuronal Hyperexitability as a Predictor of Mild Cognitive Impairment: Clinical and Neurophysiological Study

Abstract

Introduction: Mild cognitive impairment (MCI) usually is the early stage of dementia which is defined as decreasing in mental abilities such cognition, memory, and speech not too severe to interfere daily activities. MCI diagnosis is rather hard and usually assumed as normal consequences of aging. Diagnosis is usually performed through a combination of extensive testing and eliminations of other possible causes. “Seizures” or neuronal hyperexitability in the temporal lobe, transiently impair cognition and steadily damage hippocampal circuitry, leading to progressive memory loss. Objective: The objective of this study was demonstrated that EEG pattern abnormalities in the left temporal in healthy subjects, are an early sign of progressive cognitive impairment. Material and methods: This was an clinical and neurophysiology observational study in healthy adults patients with EEG pattern characterized by slow activity in left temporal region. This study lasted three years in total, being divided into two phases: recruitment (for an entire year) and follow-up after 1 year. Admission criteria were checked. The follow-up consisted of neuropsychological assessment with Mini Mental State Examination (MMSE) and MRI scan. Our analysis was based on pooled of patients from neurophysiology department in Italy from February 2010 to July 2013. The EEG activity was recorded continuously from 19 electrodes positioned according to the 10–20 International system. Results: One hundred forty patients were recruited and one hundred thirty completed the 24-month study. Of the ten patients who did not complete the study. In case group we had 60 subjects, 15 males and 45 females with sharp slow-wave in left temporal region on EEG. In control group we had 70 subjects, 30 males and 40 females with normal EEG. 57 patients (Case) and 33 patients (Controls) showed a mild cognitive impairment (MMSE ≥ 23 adjusted for age and education). 49 patients (Case) and 21 patients (Controls) with deep lacunar infarcts or subcortical white matter alterations on MRI scan. Analysis performed according to methods proposed by Koch showed that pattern EEG of slow waves significantly correlated with both variables MCI (P<0.0001) and vascular alterations (P<0.0001). Discussion: In our sample, pattern EEG was predictive for vascular abnormalities and MCI more than 50% after a few years. Conclusion: In summary, typical geographic alterations in left temporal region are “indicators” or “markers” of early cognitive impairment and may be used as prevention strategies. EEG may be considered a useful tool for early diagnosis of MCI. Further translational exploration of these issues in animals and/or humans studies over the coming years will determine new therapeutic approaches directed at selectively suppressing aberrant network excitability in the temporal lobe.