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Electroencephalographic Fractal Dimension in Healthy Ageing and Alzheimer's Disease

Lookup NU author(s): Dr Camillo Porcaro



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Brain activity is complex; a reflection of its structural and functional organization. Among other measures of complexity, the fractal dimension is emerging as being sensitive to neuronal damage secondary to neurological and psychiatric diseases. Here, we calculated Higuchi's fractal dimension (HFD) in resting-state eyes-closed electroencephalography (EEG) recordings from 41 healthy controls (age: 20-89 years) and 67 Alzheimer's Disease (AD) patients (age: 50-88 years), to investigate whether HFD is sensitive to brain activity changes typical in healthy aging and in AD. Additionally, we considered whether AD-accelerating effects of the copper fraction not bound to ceruloplasmin (also called "free" copper) are reflected in HFD fluctuations. The HFD measure showed an inverted U-shaped relationship with age in healthy people (R-2 = .575, p < .001). Onset of HFD decline appeared around the age of 60, and was most evident in central-parietal regions. In this region, HFD decreased with aging stronger in the right than in the left hemisphere (p = .006). AD patients demonstrated reduced HFD compared to age-and education-matched healthy controls, especially in temporal-occipital regions. This was associated with decreasing cognitive status as assessed by mini-mental state examination, and with higher levels of non-ceruloplasmin copper. Taken together, our findings show that resting-state EEG complexity increases from youth to maturity and declines in healthy, aging individuals. In AD, brain activity complexity is further reduced in correlation with cognitive impairment. In addition, elevated levels of non-ceruloplasmin copper appear to accelerate the reduction of neural activity complexity. Overall, HDF appears to be a proper indicator for monitoring EEG-derived brain activity complexity in healthy and pathological aging.

Publication metadata

Author(s): Smits FM, Porcaro C, Cottone C, Cancelli A, Rossini PM, Tecchio F

Publication type: Article

Publication status: Published

Journal: PLoS ONE

Year: 2016

Volume: 11

Issue: 2

Online publication date: 12/02/2016

Acceptance date: 01/02/2016

Date deposited: 26/07/2016

ISSN (electronic): 1932-6203

Publisher: Public Library of Science


DOI: 10.1371/journal.pone.0149587


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Funder referenceFunder name
PNR-CNR Aging Program
2014/RFISM - Fondazione Italiana Sclerosi Multipla