Nonlinear analysis of electroencephalogram in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a form of dementia characterized by a profound alteration in personality and social behavior and is associated with atrophy in the frontal and temporal brain regions. Despite recent advances, diagnosis of FTLD remains challenging. In the last decade, different studies have combined EEG analysis with mathematical models and theories that consider EEG signals as the result of nonlinear chaotic activity. The aim of the present study was to determine whether new nonlinear dynamic analysis can provide useful information on brain activity in FTLD patients. 19-lead EEG was recorded in patients with clinical diagnosis of FTLD and in healthy controls under two different conditions: closed eyes and open eyes. A nonlinear measure of complexity, correlation dimension (D2), was calculated. Our results show an increase in D2 in healthy individuals when the eyes are open, in keeping with an increase in information processing. Conversely, in FTLD patients, no increase in D2 occurred in the open eyes condition, and D2 was significantly lower than that observed in controls. Our results suggest that the dynamic processes underlying the EEG are less chaotic and complex in FTLD patients compared with normal individuals, thus providing important information on both brain functioning and possible clinical diagnostic applications.