Functional connectivity: a source of variance in the association between cardiorespiratory fitness and cognition?

Abstract

Over the next 20 years the number of Americans diagnosed with dementia is expected to more than double (CDC, 2007). It is, therefore, an important public health initiative to understand what factors contribute to the longevity of a healthy mind. Both default mode network (DMN) function and increased aerobic fitness have been associated with better cognitive performance and reduced incidence of Alzheimer's disease among older adults. Here we examine the association between aerobic fitness, functional connectivity in the DMN, and cognitive performance. Results showed significant age-related deficits in functional connectivity in both local and distributed DMN pathways. However, in a group of healthy elderly adults, almost half of the age-related disconnections showed increased functional connectivity as a function of aerobic fitness level. Finally, we examine the hypothesis that functional connectivity in the DMN is one source of variance in the relationship between aerobic fitness and cognition. Results demonstrate instances of both specific and global DMN connectivity mediating the relationship between fitness and cognition. We provide the first evidence for functional connectivity as a source of variance in the association between aerobic fitness and cognition, and discuss results in the context of neurobiological theories of cognitive aging and disease.

Conflict of interest statement

Disclosure statement: None of the authors have actual or potential conflicts of interest related to this work.

(c) 2010 Elsevier Ltd. All rights reserved.

Figures

Figure 1. Regional age effects for the young > elderly contrast

Statistical parametric maps shown above represent where young adults have significantly greater functional connectivity with the PCC/rsp seed compared to elderly adults. The table lists statistical peaks of the corresponding statistical maps. As shown in the table, FMC=Frontal medial cortex, MTG=middle temporal gyrus, PCC=posterior cingulate cortex, and PHG=parahippocampal gyrus. The initial PCC/rsp seed is shown in green, and the derived peaks based on between-group age effects are shown in yellow. All renderings are in radiological orientation (L=R, R=L).

Figure 2. Scatter plots for indirect path associations that showed significant mediation of the direct path between fitness and cognition

Scatter plots of associations that formed significant indirect pathways between aerobic fitness and cognition. PCCFMC = connectivity z(r) of the posterior cingulate cortex with the frontal medial cortex; MTGMFG = connectivity z(r) of the middle temporal gyrus with the left middle frontal gyrus; MFGFMC = z(r) of the left middle frontal gyrus with the frontal medial cortex. VO2 Max = maximal oxygen uptake (mL/kg/min).