Kennedy, Kristen M.

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Kristen Kennedy is an Assistant Professor in Behavioral and Brain Sciences and the Center for Vital Longevity. She also heads the Kennedy Neuroimaging of Aging and Cognition Lab. She is best known for her research in the area of cognitive neuroscience of aging. Currently, her research interests include

  • Normal aging of human brain structure and function,
  • Cognitive consequences of aging on health and lifestyle,
  • Genetic modifiers of the age-related changes in the brain and cognition

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    Frontostriatal White Matter Connectivity: Age Differences and Associations with Cognition and BOLD Modulation
    (Elsevier Inc., 2020-06-07) Webb Christina E.; Hoagey, David A.; Rodrigue, Karen M.; Kennedy, Kristen M.; 0000-0001-5373-9026 (Kennedy, KM); Webb Christina E.; Hoagey, David A.; Rodrigue, Karen M.; Kennedy, Kristen M.
    Despite the importance of cortico-striatal circuits to cognition, investigation of age effects on the structural circuitry connecting these regions is limited. The current study examined age effects on frontostriatal white matter connectivity, and identified associations with both executive function performance and dynamic modulation of blood-oxygen-level-dependent (BOLD) activation to task difficulty in a lifespan sample of 169 healthy humans aged 20–94 years. Greater frontostriatal diffusivity was associated with poorer executive function and this negative association strengthened with increasing age. Whole-brain functional magnetic resonance imaging (fMRI) analyses additionally indicated an association between frontostriatal mean diffusivity and BOLD modulation to difficulty selectively in the striatum across 2 independent fMRI tasks. This association was moderated by age, such that younger- and middle-aged individuals showed reduced dynamic range of difficulty modulation as a function of increasing frontostriatal diffusivity. Together these results demonstrate the importance of age-related degradation of frontostriatal circuitry on executive functioning across the lifespan, and highlight the need to capture brain changes occurring in early-to middle-adulthood.
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    Genetic Predisposition for Inflammation Exacerbates Effects of Striatal Iron Content on Cognitive Switching Ability in Healthy Aging
    (Academic Press Inc Elsevier Science, 2018-10-25) Daugherty, Ana M.; Hoagey, David A.; Kennedy, Kristen M.; Rodrigue, Karen M.; 0000-0001-5373-9026 (Kennedy, KM); Hoagey, David A.; Kennedy, Kristen M.; Rodrigue, Karen M.
    Non-heme iron homeostasis interacts with inflammation bidirectionally, and both contribute to age-related decline in brain structure and function via oxidative stress. Thus, individuals with genetic predisposition for inflammation may be at greater risk for brain iron accumulation during aging and more vulnerable to cognitive decline. We examine this hypothesis in a lifespan sample of healthy adults (N = 183, age 20 - 94 years) who underwent R2*-weighted magnetic resonance imaging to estimate regional iron content and genotyping of interleukin-1beta (IL-1β), a pro-inflammatory cytokine for which the T allelle of the single nucleotide polymorphism increases risk for chronic neuroinflammation. Older age was associated with greater striatal iron content that in turn accounted for poorer cognitive switching performance. Heterozygote IL-1β T-carriers demonstrated poorer switching performance in relation to striatal iron content as compared to IL-1β C/C counterparts, despite the two groups being of similar age. With increasing genetic inflammation risk, homozygote IL-1β T/T carriers had lesser age-related variance in striatal iron content as compared to the other groups but showed a similar association of greater striatal iron content predicting poorer cognitive switching. Non-heme iron and inflammation, although necessary for normal neuronal function, both promote oxidative stress that when accumulated in excess, drives a complex mechanism of neural and cognitive decline in aging.
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    Frontoparietal Cortical Thickness Mediates the Effect of COMT Val¹⁵⁸Met Polymorphism on Age-Associated Executive Function
    (Elsevier Science Inc, 2018-09-21) Miranda, Giuseppe G.; Rodrigue, Karen M.; Kennedy, Kristen M.; 0000-0001-5373-9026 (Kennedy, KM); Miranda, Giuseppe G.; Rodrigue, Karen M.; Kennedy, Kristen M.
    Proper dopamine (DA) signaling is likely necessary for maintaining optimal cognitive performance as we age, particularly in prefrontal-parietal networks and in fronto-striatal networks. Thus, reduced DA availability is a salient risk factor for accelerated cognitive aging. A common polymorphism that affects DA D1 receptor dopamine availability, COMT Val¹⁵⁸Met (rs4680), influences enzymatic breakdown of DA, with COMT Val carriers having a 3- to 4-fold reduction in synaptic DA compared to COMT Met carriers. Furthermore, dopamine receptors and postsynaptic availability are drastically reduced with aging, as is executive function performance that ostensibly relies on these pathways. Here, we investigated in 176 individuals aged 20-94 years whether: (1) COMT Val carriers differ from their Met counterparts in thickness of regional cortices receiving D1 receptor pathways: prefrontal, parietal, cingulate cortices; (2) this gene-brain association differs across the adult lifespan; and (3) COMT-related regional thinning evidences cognitive consequences. We found that COMT Val carriers evidenced thinner cortex in prefrontal, parietal, and posterior cingulate cortices than COMT Met carriers and this effect was not age-dependent. Further, we demonstrate that thickness of these regions significantly mediates the effect of COMT genotype on an executive function composite measure. These results suggest that poorer executive function performance is due partly to thinner association cortex in dopaminergic-rich regions, and particularly so in individuals who are genetically predisposed to lower postsynaptic dopamine availability, regardless of age.
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    Progress Update from the Hippocampal Subfields Group
    (Elsevier Inc., 2019-06-13) Olsen, R. K.; Carr, V. A.; Daugherty, A. M.; La Joie, R.; Amaral, R. S. C.; Amunts, K.; Augustinack, J. C.; Kennedy, Kristen M.; Rodrigue, Karen M.; Hippocampal Subfields Group; Kennedy, Kristen M.; Rodrigue, Karen M.
    Introduction: Heterogeneity of segmentation protocols for medial temporal lobe regions and hippocampal subfields on in vivo magnetic resonance imaging hinders the ability to integrate findings across studies. We aim to develop a harmonized protocol based on expert consensus and histological evidence. Methods: Our international working group, funded by the EU Joint Programme–Neurodegenerative Disease Research (JPND), is working toward the production of a reliable, validated, harmonized protocol for segmentation of medial temporal lobe regions. The working group uses a novel postmortem data set and online consensus procedures to ensure validity and facilitate adoption. Results: This progress report describes the initial results and milestones that we have achieved to date, including the development of a draft protocol and results from the initial reliability tests and consensus procedures. Discussion: A harmonized protocol will enable the standardization of segmentation methods across laboratories interested in medial temporal lobe research worldwide. ©2019 The Authors
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    Differential Aging Trajectories of Modulation of Activation to Cognitive Challenge in APOEε4 Groups: Reduced Modulation Predicts Poorer Cognitive Performance
    Foster, Chris M.; Kennedy, Kristen M.; Rodrigue, Karen M.; 0000-0001-5373-9026 (Kennedy, KM); Foster, Chris M.; Kennedy, Kristen M.; Rodrigue, Karen M.
    The present study was designed to investigate the effect of a genetic risk factor for Alzheimer's disease (AD), ApolipoproteinE ε4 (APOEε4), on the ability of the brain to modulate activation in response to cognitive challenge in a lifespan sample of healthy human adults. A community-based sample of 181 cognitively intact, healthy adults were recruited from the Dallas-Fort Worth metroplex. Thirty-oneAPOEε4+ individuals (48% women), derived from the parent sample, were matched based on sex, age, and years of education to 31 individuals who were APOEε4-negative (APOEε4-). Ages ranged from 20 to 86 years of age. Blood oxygen level-dependent functional magnetic resonance imaging was collected during the performance of a visuospatial distance judgment task with three parametric levels of difficulty. Multiple regression was used in a whole-brain analysis with age, APOE group, and their interaction predicting functional brain modulation in response to difficulty. Results revealed an interaction between age and APOE in a large cluster localized primarily to the bilateral precuneus. APOEε4- individuals exhibited age-invariant modulation in response to task difficulty, whereas APOEε4- individuals showed age-related reduction of modulation in response to increasing task difficulty compared with ε4- individuals. Decreased modulation in response to cognitive challenge was associated with reduced task accuracy as well as poorer name-face associative memory performance. Findings suggest that APOEε4 is associated with a reduction in the ability of the brain to dynamically modulate in response to cognitive challenge. Coupled with a significant genetic risk factor for AD, changes in modulation may provide additional information toward identifying individuals potentially at risk for cognitive decline associated with preclinical AD.

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