Contralateral thalamocortical connectivity is related to postural control in the uninvolved limb of older adults with history of ankle sprain.

BACKGROUND: Sensorimotor brain connectivity is often overlooked when determining relationships between postural control and motor performance following musculoskeletal injury. Thalamocortical brain connectivity is of particular interest as it represents the temporal synchrony of functionally and anatomically linked brain regions. Importantly, adults over the age of 60 are especially vulnerable to musculoskeletal injury due to age-related declines in postural control and brain connectivity. RESEARCH QUESTION: Is there a relationship between thalamocortical connectivity and static postural control in older adults with a history of LAS? METHODS: Data were analyzed from twenty older adults (mean age = 67.0 ± 4.3 yrs; 13 females) with a history of LAS. The sensorimotor network (SMN) was identified from resting-state MRI data, and a priori thalamic and postcentral gyri regions of interest were selected in order to determine left and right hemisphere thalamocortical connectivity. Balance was assessed for the involved and non-involved limbs via center of pressure velocity (COPV) in the medial-lateral (ML) and anterior-posterior (AP) directions. RESULTS: Contralateral thalamocortical connectivity was significantly associated with COPV_ML COPV_ML (r = -0.474, P = 0.05) and COPV_AP (r = -0.622, P = 0.008) in the non-involved limb. No significant association was observed between involved limb balance and contralateral thalamocortical connectivity (COPV_ML: r = -0.08, P = 0.77; COPV_AP: r = 0.12, P = 0.63). SIGNIFICANCE: A significant relationship between thalamocortical connectivity and static postural control was observed in the non-involved, but not the involved limb in older adults with a history of LAS. Findings suggest that thalamocortical connectivity may lead to or be the product of LAS.

The Relationship Between Health-Related Quality of Life and Lower-Extremity Visuomotor Reaction Time in Young Adult Women Following Ankle Sprain.

CONTEXT: Many individuals who sustain a lateral ankle sprain (LAS) fail to return to prior activity due to residual symptoms; and report elevated levels of injury-related fear, decreased function, and decreased health-related quality of life (HRQOL). Additionally, individuals with history of LAS exhibit deficits in neurocognitive functional measures like visuomotor reaction time (VMRT), which contributes to worse patient-reported outcome scores. The aim of this study was to examine the relationship between HRQOL and lower-extremity (LE) VMRT in individuals with LAS history. DESIGN: Cross-sectional. METHODS: Young adult female volunteers with history of LAS (n = 22; age = 24 [3.5] y; height = 163.1 [9.8] cm; mass = 65.1 [11.5] kg; and time since last LAS = 67.8 [50.5] mo) completed HRQOL outcomes including the following: (1) Tampa Scale of Kinesiophobia-11, (2) Fear-Avoidance Beliefs Questionnaire, (3) Penn State Worry Questionnaire, (4) modified Disablement in the Physically Active Scale, and (5) Foot and Ankle Disability Index (FADI). Additionally, participants completed a LE-VMRT task by responding to a visual stimulus using their foot to deactivate light sensors. Participants completed trials bilaterally. Separate Spearman rho correlations were performed to assess the relationship between patient-reported outcomes assessing constructs of HRQOL and LE-VRMT bilaterally. Significance was set at P < .05. RESULTS: There was a strong, significant negative correlation between FADI-Activities of Daily Living (ρ = -.68; P = .002) and FADI-Sport (ρ = -.76; P = .001) scores and injured limb LE-VMRT; moderate, significant negative correlations between the uninjured limb LE-VMRT and FADI-Activities of Daily Living (ρ = -.60; P = .01) and FADI-Sport (ρ = -.60; P = .01) scores; and moderate, significant positive correlations between the injured limb LE-VMRT and modified Disablement in the Physically Active Scale-Physical Summary Component (ρ = .52; P = .01) and modified Disablement in the Physically Active Scale-Total (ρ = .54; P = .02) scores. All other correlations were not statistically significant. CONCLUSIONS: Young adult women with history of LAS demonstrated an association between self-reported constructs of HRQOL and LE-VMRT. As LE-VMRT is a modifiable injury risk factor, future studies should examine the effectiveness of interventions designed to improve LE-VMRT and the impact on self-reported HRQOL.

Feasibility of Contrasting Brain Connectivity Patterns in Cognitive and Motor Cerebral Networks to Clinical Outcomes in Patients Surviving Acute Respiratory Failure: A Pilot Study.

BACKGROUND: There is a paucity of research regarding the feasibility and association of cerebral cortex function to patient outcomes after acute respiratory failure (ARF). PURPOSE: To determine the feasibility of functional connectivity measures and examine the association of functional connectivity to a multifaceted battery of outcomes in survivors of ARF. METHODS: Eight ARF patients (age:58±3.7, ICU days:10.4±8.6) completed functional magnetic resonance imaging (fMRI), cognitive, physical-function, anxiety, depression, and driving simulator tests at one month post-hospital discharge. Pearson's correlations assessed the relationship between functional connectivity within the default mode network (FPN), sensorimotor network (SMN), and frontoparietal network (FPN) to outcomes. RESULTS: Low physical-function (r=0.75, p=0.03) and divided-attention (r=-0.86, p=0.03) during the driving simulator task correlated with low FPN connectivity. Low SMN connectivity demonstrated relationships to slower gait speed (r=0.82, p=0.01) and low short physical performance battery (SPPB) scores (r=0.81, p=0.01). CONCLUSIONS: fMRI is feasible to assess ARF patients' post-ICU limitations, as low post-ARF brain connectivity may be linked to low physical function, providing potential development of therapeutic interventions.

Resting state functional connectivity responses post-mild traumatic brain injury: a systematic review.

Mild traumatic brain injuries (mTBI) are associated with functional network connectivity alterations throughout recovery. Yet, little is known about the adaptive or maladaptive nature of post-mTBI connectivity and which networks are predisposed to altered function and adaptation. The objective of this review was to determine functional connectivity changes post-mTBI and to determine the adaptive or maladaptive nature of connectivity through direct comparisons of connectivity and behavioral data. Literature was systematically searched and appraised for methodological quality. A total of 16 articles were included for review. There was conflicting evidence of post-mTBI connectivity responses as decreased connectivity was noted in 4 articles, 6 articles reported increased connectivity, 5 reported a mixture of increased and decreased connectivity, while 1 found no differences in connectivity. Supporting evidence for adaptive post-mTBI increases in connectivity were found, particularly in the frontoparietal, cerebellar, and default mode networks. Although initial results are promising, continued longitudinal research that systematically controls for confounding variables and that standardizes methodologies is warranted to adequately understand the neurophysiological recovery trajectory of mTBI.

Cardiorespiratory fitness diminishes the effects of age on white matter hyperintensity volume.

White matter hyperintensities (WMHs) are among the most commonly observed marker of cerebrovascular disease. Age is a key risk factor for WMH development. Cardiorespiratory fitness (CRF) is associated with increased vessel compliance, but it remains unknown if high CRF affects WMH volume. This study explored the effects of CRF on WMH volume in community-dwelling older adults. We further tested the possibility of an interaction between CRF and age on WMH volume. Participants were 76 adults between the ages of 59 and 77 (mean age = 65.36 years, SD = 3.92) who underwent a maximal graded exercise test and structural brain imaging. Results indicated that age was a predictor of WMH volume (beta = .32, p = .015). However, an age-by-CRF interaction was observed such that higher CRF was associated with lower WMH volume in older participants (beta = -.25, p = .040). Our findings suggest that higher levels of aerobic fitness may protect cerebrovascular health in older adults.

Health-Related Quality of Life Among Middle-Aged Adults With Chronic Ankle Instability, Copers, and Uninjured Controls.

CONTEXT: People with chronic ankle instability (CAI) display a lower regional and global health-related quality of life (HRQoL). Examinations of HRQoL outcomes associated with CAI have addressed younger adults, restricting our understanding of the long-term consequences of CAI. OBJECTIVE: To compare ankle regional and global HRQoL in middle-aged participants with and those without CAI. DESIGN: Cross-sectional study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 59 middle-aged volunteers, consisting of 18 with CAI (age = 50.2 ± 9.3 years), 17 who were ankle-sprain copers (age = 54.5 ± 8.7 years), and 24 uninjured controls (age = 56.7 ± 10.0 years). MAIN OUTCOME MEASURE(S): Participants completed the Foot and Ankle Disability Index (FADI) and the Patient-Reported Outcomes Measurement Information System Adult Profile. Regional HRQoL was assessed using the FADI Activities of Daily Living and Sport subscales. Global HRQoL was measured using the 43-item Patient-Reported Outcomes Measurement Information System Adult Profile, which contains 7 short forms-Physical Function, Pain Interference, Fatigue, Depression, Sleep Disturbance, Anxiety, and Ability to Participate in Social Roles and Activities. Separate Kruskal-Wallis tests were used to determine between-groups differences. RESULTS: Middle-aged participants with CAI had lower scores on both subscales of the FADI than the coper and control groups (all P values <.001). Participants with CAI scored lower on the Physical Function (U = 116.0, z = -2.78, P = .005) and Ability to Participate in Social Roles and Activities (U = 96.0, z = -3.09, P = .002) subscales but higher on the Pain Interference (U = 144.0, z = -2.36, P = .02), Fatigue (U = 110.0, z = -2.72, P = .006), and Depression (U = 110.5, z = -2.91, P = .004) subscales than the control group. Participants with CAI also scored lower on the Physical Function (U = 74.5, z = -2.79, P = .005) and Ability to Participate in Social Roles and Activities (U = 55.0, z = -3.29, P = .001) subscales but higher on the Fatigue (U = 90.0, z = -2.09, P = .04) and Depression (U = 96.5, z = -1.97, P = .048) subscales than the coper group. CONCLUSIONS: Middle-aged participants with CAI displayed worse ankle regional and global HRQoL than their age-matched healthy counterparts and copers. These results demonstrated that CAI can affect HRQoL outcomes in middle-aged adults.

Decreased ankle and hip isometric peak torque in young and middle-aged adults with chronic ankle instability.

OBJECTIVES: To compare ankle, knee and hip isometric peak torque between young and middle-aged adults with CAI, copers and un-injured controls. DESIGN: Cross-sectional. SETTING: Research Laboratory. PARTICIPANTS: One hundred fifty-six young and middle-aged adults with or without CAI volunteered. MAIN OUTCOME MEASURES: A handheld dynamometer measured isometric dorsiflexion, plantarflexion, knee extension, hip extension and hip abduction peak force during a 5 s trial. Average peak torque was calculated and normalized to body mass. RESULTS: A significant Age by Injury interaction for dorsiflexion suggest middle-aged un-injured controls (p < 0.001) and copers (p < 0.001) had lower isometric peak torque compared to their young adult counterparts, but there were no differences between young and middle-aged adults with CAI (p > 0.05). Significant Injury main effects suggest the CAI group had decreased plantarflexion (p = 0.004) and hip extension (p = 0.010) strength compared to un-injured controls, but not copers (p > 0.05). Significant Age main effects for all primary outcome measures were observed, indicating peak torque decreased with age (p < 0.05). CONCLUSIONS: Regardless of age, isometric ankle and hip peak torque was lower in participants with CAI compared to un-injured controls, but not copers. These findings provide further evidence towards the impact of CAI in both young and middle-aged adults.

Bend Don't Break: Stretching Improves Scores on a Battery of Fall Assessment Tools in Older Adults.

CONTEXT: Falls and loss of autonomy are often attributed in large part to musculoskeletal impairments in later adulthood. Age-related declines in flexibility contribute to late adulthood musculoskeletal impairment. The novel sitting-rising test has been proposed to be a quick, effective screening of musculoskeletal fitness, fall risk, and all-cause mortality in older adults. The timed up and go and 5 times sit-to-stand tests are two of the 3 most evidence-supported performance measures to assess fall risk. OBJECTIVE: This study aimed to determine if 5 weeks of flexibility training could increase sitting-rising test, timed up and go, and 5 times sit-to-stand scores in community-dwelling older adults. PARTICIPANTS: Forty-seven adults aged 60 years and older (mean age = 66.7 y, SD = 4.1) participated in this study. Participants completed a static stretching protocol consisting of 3 weekly 1-hour stretching sessions. RESULTS: The protocol improved flexibility as seen in sit-and-reach scores and improved scores on all outcome variables. Specifically, there was a significant increase in sitting-rising test scores from preintervention (M = 7.45, SD = 1.45) to postintervention (M = 8.04, SD = 1.36), t(42) = -5.21, P < .001. Timed up and go scores demonstrated a significant decrease from preintervention (M = 8.85, SD = 1.32) to postintervention (M = 8.20, SD = 1.35), t(46) = 5.10, P < .001. Five times sit-to-stand scores demonstrated a significant decrease from preintervention (M = 12.57, SD = 2.68) to postintervention (M = 10.46, SD = 2.06), t(46) = 6.62, P < .001. Finally, significant increases in sit-and-reach scores were associated with improved functional performance (r = -.308, P = .03). CONCLUSION: Findings suggest that flexibility training can be an effective mode of low-level exercise to improve functional outcomes. Static stretching may help to improve musculoskeletal health, promote autonomy, and decrease mortality in community-dwelling older adults.

Non-fasting High-Density Lipoprotein Is Associated With White Matter Microstructure in Healthy Older Adults.

A growing body of evidence indicates that biomarkers of cardiovascular risk may be related to cerebral health. However, little is known about the role that non-fasting lipoproteins play in assessing age-related declines in a cerebral biomarker sensitive to vascular compromise, white matter (WM) microstructure. High-density lipoprotein cholesterol (HDL-C) is atheroprotective and low-density lipoprotein cholesterol (LDL-C) is a major atherogenic lipoprotein. This study explored the relationships between non-fasting levels of cholesterol and WM microstructure in healthy older adults. A voxelwise and region of interest approach was used to determine the relationship between cholesterol and fractional anisotropy (FA). Participants included 87 older adults between the ages of 59 and 77 (mean age = 65.5 years, SD = 3.9). Results indicated that higher HDL-C was associated with higher FA in diffuse regions of the brain when controlling for age, sex, and body mass index (BMI). HDL-C was also positively associated with FA in the corpus callosum and fornix. No relationship was observed between LDL-C and FA. Findings suggest that a modifiable lifestyle variable associated with cardiovascular health may help to preserve cerebral WM.

Decreased dynamic balance and dorsiflexion range of motion in young and middle-aged adults with chronic ankle instability.

OBJECTIVES: The purpose of this study was to compare dynamic balance and weight-bearing dorsiflexion range of motion between young and middle-aged adults with and without chronic ankle instability. DESIGN: Cross-sectional. METHODS: One hundred and two young adults were classified as either having chronic ankle instability (n = 38), coper (n = 27) or a healthy-control (n = 37). A total of 55 middle-aged adults were identified as having chronic ankle instability (n = 16), coper (n = 15) or a healthy-control (n = 24). Participants completed the weight-bearing lunge test and the anterior, posteromedial and posterolateral reach directions of the star excursion balance test. RESULTS: Middle-aged adults had shorter reach distances for each direction of the star excursion balance test compared to the young adults (p < 0.001). Regardless of age, participants with chronic ankle instability performed worse on the star excursion balance test compared to the coper (p < 0.05) and healthy-control group (p < 0.05). Similarly, participants with chronic ankle instability had less dorsiflexion compared to healthy-controls (p < 0.05), but not the coper group (p > 0.05). CONCLUSIONS: Deficits in dynamic postural control do not continue to decline with advancing age in individuals with chronic ankle instability, however, these impairments appear to continue to persist compared to uninjured controls.

Distinct White Matter Changes Associated with Cerebrospinal Fluid Amyloid-ß1-42 and Hypertension.

BACKGROUND: Alzheimer's disease (AD) pathology and hypertension (HTN) are risk factors for development of white matter (WM) alterations and might be independently associated with these alterations in older adults. OBJECTIVE: To evaluate the independent and synergistic effects of HTN and AD pathology on WM alterations. METHODS: Clinical measures of cerebrovascular disease risk were collected from 62 participants in University of Kentucky Alzheimer's Disease Center studies who also had cerebrospinal fluid (CSF) sampling and MRI brain scans. CSF Aß1-42 levels were measured as a marker of AD, and fluid-attenuated inversion recovery imaging and diffusion tensor imaging were obtained to assess WM macro- and microstructural properties. Linear regression analyses were used to assess the relationships among WM alterations, cerebrovascular disease risk, and AD pathology. Voxelwise analyses were performed to examine spatial patterns of WM alteration associated with each pathology. RESULTS: HTN and CSF Aß1-42 levels were each associated with white matter hyperintensities (WMH). Also, CSF Aß1-42 levels were associated with alterations in normal appearing white matter fractional anisotropy (NAWM-FA), whereas HTN was marginally associated with alterations in NAWM-FA. Linear regression analyses demonstrated significant main effects of HTN and CSF Aß1-42 on WMH volume, but no significant HTN×CSF Aß1-42 interaction. Furthermore, voxelwise analyses showed unique patterns of WM alteration associated with hypertension and CSF Aß1-42. CONCLUSION: Associations of HTN and lower CSF Aß1-42 with WM alteration were statistically and spatially distinct, suggesting independent rather than synergistic effects. Considering such spatial distributions may improve diagnostic accuracy to address each underlying pathology.

Dynamic range of frontoparietal functional modulation is associated with working memory capacity limitations in older adults.

Older adults tend to over-activate regions throughout frontoparietal cortices and exhibit a reduced range of functional modulation during WM task performance compared to younger adults. While recent evidence suggests that reduced functional modulation is associated with poorer task performance, it remains unclear whether reduced range of modulation is indicative of general WM capacity-limitations. In the current study, we examined whether the range of functional modulation observed over multiple levels of WM task difficulty (N-Back) predicts in-scanner task performance and out-of-scanner psychometric estimates of WM capacity. Within our sample (60-77years of age), age was negatively associated with frontoparietal modulation range. Individuals with greater modulation range exhibited more accurate N-Back performance. In addition, despite a lack of significant relationships between N-Back and complex span task performance, range of frontoparietal modulation during the N-Back significantly predicted domain-general estimates of WM capacity. Consistent with previous cross-sectional findings, older individuals with less modulation range exhibited greater activation at the lowest level of task difficulty but less activation at the highest levels of task difficulty. Our results are largely consistent with existing theories of neurocognitive aging (e.g. CRUNCH) but focus attention on dynamic range of functional modulation asa novel marker of WM capacity-limitations in older adults.

Endothelial Function Is Associated with White Matter Microstructure and Executive Function in Older Adults.

Age-related declines in endothelial function can lead to cognitive decline. However, little is known about the relationships between endothelial function and specific neurocognitive functions. This study explored the relationship between measures of endothelial function (reactive hyperemia index; RHI), white matter (WM) health (fractional anisotropy, FA, and WM hyperintensity volume, WMH), and executive function (Trail Making Test (TMT); Trail B - Trail A). Participants were 36 older adults between the ages of 59 and 69 (mean age = 63.89 years, SD = 2.94). WMH volume showed no relationship with RHI or executive function. However, there was a positive relationship between RHI and FA in the genu and body of the corpus callosum. In addition, higher RHI and FA were each associated with better executive task performance. Tractography was used to localize the WM tracts associated with RHI to specific portions of cortex. Results indicated that the RHI-FA relationship observed in the corpus callosum primarily involved tracts interconnecting frontal regions, including the superior frontal gyrus (SFG) and frontopolar cortex, linked with executive function. These findings suggest that superior endothelial function may help to attenuate age-related declines in WM microstructure in portions of the corpus callosum that interconnect prefrontal brain regions involved in executive function.

Development, validation and application of a new fornix template for studies of aging and preclinical Alzheimer's disease.

We developed a merged younger-older adult template of the fornix and demonstrated its utility for studies of aging and preclinical Alzheimer's disease (AD). In Experiment 1, probabilistic tractography was used to reconstruct the fornix in younger and older adults and successful streamlines were then averaged to create a merged template in standard space. The new template includes the majority of the fornix from the hippocampal formation to the subcallosal region and the thalamus/hypothalamus. In Experiment 2, the merged template was validated as an appropriate measure for studies of aging, with comparisons against manual tracing measures indicating identical spatial coverage in younger and older adult groups. In Experiment 3, the merged template was found to outperform age-specific templates in measures of sensitivity and specificity computed on diffusion tensor imaging data of an independent participant cohort. In Experiment 4, relevance to preclinical AD was demonstrated via associations between fractional anisotropy within the new fornix template and cerebrospinal fluid markers of AD pathology (Aß42 and the t-tau/Aß42 ratio) in a third independent cohort of cognitively normal older adults. Our new template provides an appropriate measure for use in future studies seeking to characterize microstructural alterations in the fornix associated with aging and preclinical AD.

Cardiorespiratory fitness modifies the relationship between myocardial function and cerebral blood flow in older adults.

A growing body of evidence indicates that cardiorespiratory fitness attenuates some age-related cerebral declines. However, little is known about the role that myocardial function plays in this relationship. Brain regions with high resting metabolic rates, such as the default mode network (DMN), may be especially vulnerable to age-related declines in myocardial functions affecting cerebral blood flow (CBF). This study explored the relationship between a measure of myocardial mechanics, global longitudinal strain (GLS), and CBF to the DMN. In addition, we explored how cardiorespiratory affects this relationship. Participants were 30 older adults between the ages of 59 and 69 (mean age=63.73years, SD=2.8). Results indicated that superior cardiorespiratory fitness and myocardial mechanics were positively associated with DMN CBF. Moreover, results of a mediation analysis revealed that the relationship between GLS and DMN CBF was accounted for by individual differences in fitness. Findings suggest that benefits of healthy heart function to brain function are modified by fitness.

White matter microstructure contributes to age-related declines in task-induced deactivation of the default mode network.

Task-induced deactivations within the brain's default mode network (DMN) are thought to reflect suppression of endogenous thought processes to support exogenous goal-directed task processes. Older adults are known to show reductions in deactivation of the DMN compared to younger adults. However, little is understood about the mechanisms contributing to functional dysregulation of the DMN in aging. Here, we explored the relationships between functional modulation of the DMN and age, task performance and white matter (WM) microstructure. Participants were 117 adults ranging from 25 to 83 years old who completed an fMRI task switching paradigm, including easy (single) and difficult (mixed) conditions, and underwent diffusion tensor imaging (DTI). The fMRI results revealed an age by condition interaction (ß = -0.13, t = -3.16, p = 0.002) such that increasing age affected deactivation magnitude during the mixed condition (ß = -0.29, t = -3.24 p = 0.002) but not the single condition (p = 0.58). Additionally, there was a WM by condition interaction (ß = 0.10, t = 2.33, p = 0.02) such that decreasing WM microstructure affected deactivation magnitude during the mixed condition (ß = 0.30, t = 3.42 p = 0.001) but not the single condition (p = 0.17). Critically, mediation analyses indicated that age-related reductions in WM microstructure accounted for the relationship between age and DMN deactivation in the more difficult mixed condition. These findings suggest that age-related declines in anatomical connectivity between DMN regions contribute to functional dysregulation within the DMN in older adults.

Longitudinal alterations to brain function, structure, and cognitive performance in healthy older adults: A fMRI-DTI study.

Cross-sectional research has shown that older adults tend to have different frontal cortex activation patterns, poorer brain structure, and lower task performance than younger adults. However, relationships between longitudinal changes in brain function, brain structure, and cognitive performance in older adults are less well understood. Here we present the results of a longitudinal, combined fMRI-DTI study in cognitive normal (CN) older adults. A two time-point study was conducted in which participants completed a task switching paradigm while fMRI data was collected and underwent the identical scanning protocol an average of 3.3 years later (SD=2 months). We observed longitudinal fMRI activation increases in bilateral regions of lateral frontal cortex at time point 2. These fMRI activation increases were associated with longitudinal declines in WM microstructure in a portion of the corpus callosum connecting the increasingly recruited frontal regions. In addition, the fMRI activation increase in the left VLPFC was associated with longitudinal increases in response latencies. Taken together, our results suggest that local frontal activation increases in CN older adults may in part reflect a response to reduced inter-hemispheric signaling mechanisms.

Evidence for reduced efficiency and successful compensation in older adults during task switching.

Older adults often show different functional activation patterns than younger adults in prefrontal cortex (PFC) when performing cognitive control tasks. These differences include age-related increases in PFC activation magnitude and reorganized PFC functional connectivity (fC) patterns. However, it remains unclear whether age-related alterations in brain activation patterns reflect a positive mechanism (e.g., compensatory response) or a sign of brain dysfunction (e.g., reduced efficiency). Here we used functional magnetic resonance imaging (fMRI) to compare PFC activation magnitudes and PFC connectivity patterns between younger and older adult groups during performance of a task switching paradigm. Results indicated age-related increases both in PFC activation magnitudes and in PFC fC with inferotemporal (IT) regions. However, these age-related fMRI increases were differentially associated with task performance. Whereas increased PFC activation magnitudes tended to be either unrelated to task RT or associated with poorer task performance, increased PFC-IT connectivity was associated with better task performance in older adults. Our results suggest that age-related reductions in efficiency and successful compensation can co-exist in older adults in the context of the same task.

Reduced frontal cortex efficiency is associated with lower white matter integrity in aging.

Increased frontal cortex activation during cognitive task performance is common in aging but remains poorly understood. Here we explored patterns of age-related frontal brain activations under multiple task performance conditions and their relationship to white matter (WM) microstructure. Groups of younger (N = 28) and older (N = 33) participants completed a task-switching paradigm while functional magnetic resonance imaging (fMRI) was performed, and rested while diffusion tensor imaging was performed. Results from fMRI analyses indicated age-related increases in frontal brain activations under conditions of poorer performance in the older group (the nonswitch and switch conditions) and for a contrast in which behavioral performance was equated (older group nonswitch condition vs. younger group switch condition). Within the older adult group, higher frontal activation was associated with poorer behavioral performance under all task conditions. In 2 regions in right frontal cortex, blood oxygen level-dependent (BOLD) magnitudes were negatively correlated with WM integrity in tracts connecting these structures with other task-relevant frontoparietal and striatal regions. Our results link age-related declines in the efficiency of frontal cortex functioning with lower WM integrity in aging.

Conflict adaptation in prefrontal cortex: now you see it, now you don't.

Daily life requires people to monitor and resolve conflict arising from distracting information irrelevant to current goals. The highly influential conflict monitoring theory (CMT) holds that the anterior cingulate cortex (ACC) detects conflict and subsequently triggers the dorsolateral prefrontal cortex (DLPFC) to regulate that conflict. Multiple lines of evidence have provided support for CMT. For example, performance is faster on incongruent trials that follow other incongruent trials (iI), and is accompanied by reduced ACC and increased DLPFC activation (the conflict adaptation effect). In this fMRI study, we explored whether ACC-DLPFC conflict signaling can result in behavioral adjustments beyond on-line contexts. Participants completed a modified version of the Stroop conflict adaptation paradigm which tested for conflict adaptation effects on the current (N) trial associated with not only the immediately preceding (N - 1) trial, but also 2-back (N - 2) trials. Results demonstrated evidence for direct relationships between ACC activity on N - 2 trials and both N trial DLPFC activity and behavioral adjustment when intervening trials were congruent (i.e., icI). In contrast, when N - 1 trials were incongruent (i.e., iiI), ACC-DLPFC signaling failed and conflict adaptation was absent. These results provide new evidence demonstrating that the conflict monitor-controller maintains previously experienced conflict in the service of subsequent behavioral adjustment. However, the processing of multiple, temporally proximal conflict signals takes a toll on the working memory (WM) system, which appears to require resetting in order to adapt our behavior to frequently changing environmental demands.