Abstract
Higher general intelligence attenuates age-associated cognitive decline and the risk of dementia. Thus, intelligence has been associated with cognitive reserve or resilience in normal aging. Neurophysiologically, intelligence is considered as a complex capacity that is dependent on a global cognitive network rather than isolated brain areas. An association of structural as well as functional brain network characteristics with intelligence has already been reported in young adults. We investigated the relationship between global structural brain network properties, general intelligence and age in a group of 43 cognitively healthy elderly, age 60–85 years. Individuals were assessed cross-sectionally using Wechsler Adult Intelligence Scale-Revised (WAIS-R) and diffusion-tensor imaging. Structural brain networks were reconstructed individually using deterministic tractography, global network properties (global efficiency, mean shortest path length, and clustering coefficient) were determined by graph theory and correlated to intelligence scores within both age groups. Network properties were significantly correlated to age, whereas no significant correlation to WAIS-R was observed. However, in a subgroup of 15 individuals aged 75 and above, the network properties were significantly correlated to WAIS-R. Our findings suggest that general intelligence and global properties of structural brain networks may not be generally associated in cognitively healthy elderly. However, we provide first evidence of an association between global structural brain network properties and general intelligence in advanced elderly. Intelligence might be affected by age-associated network deterioration only if a certain threshold of structural degeneration is exceeded. Thus, age-associated brain structural changes seem to be partially compensated by the network and the range of this compensation might be a surrogate of cognitive reserve or brain resilience.
Highlights
The main cognitive domains, including memory, attention, executive function, and information processing speed, are delimitable but not independent from each other
Subjects A sample of 43 cognitively healthy elderly aged 60 to 85 years had agreed to participate in the study that was conducted at the Department of Psychiatry and Psychotherapy, University Medical Center of Mainz, Germany
Long-range pathways connecting locally dense clusters are crucial for short paths in small world networks [52], lower edge weights in these long-range paths may lead to overall longer path length in the network
Summary
The main cognitive domains, including memory, attention, executive function, and information processing speed, are delimitable but not independent from each other. The common variance that is shared among cognitive domains is captured by the construct of general intelligence [1,2,3]. General intelligence has been shown to be a robust predictor of several life outcomes, including educational and occupational success, health-conscious behavior and mortality [1,4,5]. General intelligence is known to attenuate the degree of ageassociated cognitive decline and the risk of developing late-onset Alzheimer’s disease (AD) and has been proposed to be an important component of cognitive reserve [6,7,8,9]. Neuroscientific research has strongly contributed to the understanding of the biological basis of human general intelligence. Estimates of how much of the variance in general intelligence can be attributed to genetic variations range from 30 to 80% [2]
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