Association of Structural Global Brain Network Properties with Intelligence in Normal Aging

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.

更高的一般智力（general intelligence）可缓解与年龄相关的认知衰退及痴呆风险。因此，在正常衰老过程中，智力与认知储备（cognitive reserve）或脑韧性（brain resilience）密切相关。从神经生理学角度而言，智力被视为一种依赖于整体认知网络而非孤立脑区的复杂能力。此前已有研究证实，青年人的脑结构与功能网络特征与智力水平存在关联。本研究纳入43名年龄在60至85岁之间的认知健康老年人，旨在探究整体脑结构网络属性、一般智力与年龄三者间的关联。所有受试者均通过韦氏成人智力量表修订版（Wechsler Adult Intelligence Scale-Revised, WAIS-R）与弥散张量成像（diffusion-tensor imaging）进行横断面评估。研究人员采用确定性纤维束追踪法（deterministic tractography）分别重构个体脑结构网络，通过图论（graph theory）计算全局网络属性（包括全局效率、平均最短路径长度与聚类系数），并在两个年龄亚组中分析其与智力得分的相关性。结果显示，脑网络属性与年龄呈显著相关，但未观察到其与WAIS-R得分存在显著关联。然而，在15名75岁及以上的亚组受试者中，脑网络属性与WAIS-R得分呈显著相关。本研究结果表明，在认知健康的老年人群中，一般智力与脑结构网络整体属性之间可能并不存在普遍关联。但本研究首次为高龄老年人群的脑结构网络整体属性与一般智力之间的关联提供了实证依据。仅当结构退变达到特定阈值时，与年龄相关的网络退变才会对智力产生影响。由此可见，与年龄相关的脑结构变化似乎可通过脑网络得到部分代偿，而这种代偿的范围或可作为认知储备或脑韧性的替代标志物。