Cortico-Striatal Functional Connectivity Reflects Changes in Subjective Energy and Tiredness

Subjective feelings of energy and tiredness may reflect different neural processes. Functional connectivity (FC) was measured in 272 HealthABC participants via resting state functional MRI in striatal-associative, striatal-limbic and striatal-sensorimotor networks. Subjective energy level (scored 1-10) and tiredness (tired/not-tired) during the prior month were collected via self-report from year 2 to year 10 (mean energy follow-up=8 years, tiredness follow-up=7 years). Participants who never reported being tired during follow-up (N=119) had significantly lower FC in the striatal-limbic network (mean difference [95%CI]: -0.055 [-0.1020,-0.00879], p=0.02). Participants with stable energy level over time (N=94, defined as decline <1.0 SD below the mean) had significantly higher FC in the striatal-associative network (mean difference [95% CI]: 0.041 [0.00192,0.0807], p=0.04). Associations were similar when adjusted for brain atrophy, demographics, and education. Although based on subjective measures, the distinct spatial patterns of these associations support our hypothesis that neural basis of energy and fatigue may differ.

Energy Decline May Predict Mild Parkinsonian Signs in Community-Dwelling Older Adults

Mild Parkinsonian Signs (MPS) are common in older adults without overt neurological disease. MPS are often progressive and predict disability and dementia, yet little is known about predictors for MPS. Low self-reported energy is associated with mobility impairment, which is a hallmark of MPS. Yet whether self-reported energy relates to MPS is unknown. We explored the association of changes in self-reported energy with MPS in 293 participants (aged 83 ± 2.8 years, 58% women, 61% White) free of dementia and Parkinson’s Disease in the Health, Aging and Body Composition Study. Self-reported energy was assessed on a 0-10 scale annually between Year 2 and Year 10 (mean follow-up: 8 years) and its slope was estimated via linear mixed effects models. MPS were evaluated at Year 10 based on the Unified Parkinson Disease Rating Scale motor component. On average, self-reported energy declined 0.06 points per year. In a linear regression model adjusted for age, fatigue, and comorbidities, those with MPS had steeper SEL decline (β [Standard Error] = -0.358 [0.119]) in the prior eight years than those without MPS. Thus, declining self-reported energy may be a risk factor for MPS. Self-reported energy is easily evaluated in routine clinic visits, and may be a modifiable risk factor that can be targeted to reduce the incidence of MPS.

Mild Parkinsonian Signs Are Related to Lower Cortico-Striatal Connectivity in Executive Networks

Mild Parkinsonian signs (MPS) affect up to 24% of community-dwelling older adults. We hypothesize that MPS are associated with Parkinson’s-like alterations of functional connectivity (FC) in sensorimotor, executive, and reward cortico-striatal networks. Participants (N=266; mean age=83; 57% female) without Parkinson’s completed resting-state fMRI and Unified Parkinsonian Disease Rating Scale (UPDRS). FC between striatum and cortex was measured within each network. Logistic regression tested associations of each network’s FC with MPS (UPDRS>0), adjusted for MPS risk factors, then including white matter hyperintensities (WMH). MPS was associated with lower cortical-striatal FC in the left executive cortico-striatal network (OR [95%CI]: 0.188 [0.043,0.824]). Association survived adjusting for risk factors (0.162 [0.030,0.874]) but was attenuated after including WMH (0.209 [0.036, 1.200]). In stratified analyses, left executive cortico-striatal FC was associated with MPS only for those with higher WMH (0.077 [0.010,0.599]). Future work should examine whether higher FC protects against the influence of WMH on MPS.

Diffusion Tensor Imaging of the Olfactory System in Older Adults With and Without Hyposmia

Objectives: To compare gray matter microstructural characteristics of higher-order olfactory regions among older adults with and without hyposmia.

Methods: Data from the Brief Smell Identification Test (BSIT) were obtained in 1998–99 for 265 dementia-free adults from the Health, Aging, and Body Composition study (age at BSIT: 74.9 ± 2.7; 62% White; 43% male) who received 3T diffusion tensor imaging in 2006–08 [Interval of time: mean (SD): 8.01 years (0.50)], Apolipoprotein (ApoEε4) genotypes, and repeated 3MS assessments until 2011–12. Cognitive status (mild cognitive impairment, dementia, normal cognition) was adjudicated in 2011–12. Hyposmia was defined as BSIT ≤ 8. Microstructural integrity was quantified by mean diffusivity (MD) in regions of the primary olfactory cortex amygdala, orbitofrontal cortex (including olfactory cortex, gyrus rectus, the orbital parts of the superior, middle, and inferior frontal gyri, medial orbital part of the superior frontal gyrus), and hippocampus. Multivariable regression models were adjusted for total brain atrophy, demographics, cognitive status, and ApoEε4 genotype.

Results: Hyposmia in 1998–99 (n = 57, 21.59%) was significantly associated with greater MD in 2006–08, specifically in the orbital part of the middle frontal gyrus, and amygdala, on the right [adjusted beta (p value): 0.414 (0.01); 0.527 (0.01); respectively].

Conclusion: Older adults with higher mean diffusivity in regions important for olfaction are more likely to have hyposmia up to ten years prior. Future studies should address whether hyposmia can serve as an early biomarker of brain microstructural abnormalities for older adults with a range of cognitive functions, including those with normal cognition.

Mild parkinsonian signs, energy decline, and striatal volume in community-dwelling older adults

BACKGROUND

Mild Parkinsonian Signs (MPS), highly prevalent in older adults, predict disability. It is unknown whether energy decline, a predictor of mobility disability, is also associated with MPS. We hypothesized that those with MPS had greater decline in self-reported energy levels (SEL) than those without MPS, and that SEL decline and MPS share neural substrates.

METHODS

Using data from the Health, Aging and Body Composition Study, we analyzed 293 Parkinson's Disease-free participants (83±3 years old, 39% Black, 58% women) with neuroimaging data, MPS evaluation by Unified Parkinson Disease Rating Scale in 2006-2008, and ≥ 3 measures of SEL since 1999-2000. Individual SEL slopes were computed via linear mixed models. Associations of SEL slopes with MPS were tested using logistic regression models. Association of SEL slope with volume of striatum, sensorimotor, and cognitive regions were examined using linear regression models adjusted for normalized total gray matter volume. Models were adjusted for baseline SEL, mobility, demographics, and comorbidities.

RESULTS

Compared to those without MPS (n=165), those with MPS (n=128) had 37% greater SEL decline in the prior eight years (p=0.001). Greater SEL decline was associated with smaller right striatal volume (adjusted standardized β=0.126, p=0.029). SEL decline was not associated with volumes in other regions. The association of SEL decline with MPS remained similar after adjustment for right striatal volume (adjusted OR=2.03, 95% CI: 1.16 - 3.54).

CONCLUSION

SEL decline may be faster in those with MPS. Striatal atrophy may be important for declining energy but does not explain the association with MPS.

Cognition and Cerebrovascular Reactivity in Midlife Women With History of Preeclampsia and Placental Evidence of Maternal Vascular Malperfusion

Background: Preeclampsia is emerging as a sex-specific risk factor for cerebral small vessel disease (SVD) and dementia, but the reason is unknown. We assessed the relationship of maternal vascular malperfusion (MVM), a marker of placental SVD, with cognition and cerebral SVD in women with and without preeclampsia. We hypothesized women with both preeclampsia and MVM would perform worst on information processing speed and executive function.

Methods: Women (n = 45; mean 10.5 years post-delivery; mean age: 41 years; 42.2% Black) were classified as preeclampsia-/MVM-, preeclampsia+/MVM-, or preeclampsia+/MVM+. Information processing speed, executive function, and memory were assessed. In a pilot sub-study of cerebrovascular reactivity (CVR; n = 22), cerebral blood flow during room-air breathing and breath-hold induced hypercapnia were obtained via arterial spin labeling MRI. Non-parametric tests and regression models were used to test associations.

Results: Between-group cognitive differences were significant for information processing speed (p = 0.02); preeclampsia+/MVM+ had the lowest scores. Cerebral blood flow increased from room-air to breath-hold, globally and in all regions in the three groups, except the preeclampsia+/MVM+ parietal region (p = 0.12). Lower parietal CVR (less change from room-air breathing to breath-holding) was correlated with poorer information processing speed (partial ρ = 0.63, p = 0.005) and executive function (ρ = 0.50, p = 0.03) independent of preeclampsia/MVM status.

Conclusion: Compared to women without preeclampsia and MVM, midlife women with both preeclampsia and MVM have worse information processing speed and may have blunted parietal CVR, an area important for information processing speed and executive function. MVM in women with preeclampsia is a promising sex-specific indicator of cerebrovascular integrity in midlife.

Mouse Navigation Strategies for Odor Source Localization

Navigating an odor landscape is a critical behavior for the survival of many species, including mice. An ethologically relevant mouse behavior is locating food using information about odor concentration. To approximate this behavior, we used an open field odor-based spot-finding task indoors with little wind, examining navigation strategies as mice search for and approach an odor source. After mice were trained to navigate to odor sources paired with food reward, we observed behavioral changes consistent with localization 10-45 cm away from the source. These behaviors included orientation toward the source, decreased velocity, and increased exploration time. We also found that the amplitude of 'casting,' which we define as lateral back and forth movement of the nose, increased with proximity to the source. Based on these observations, we created a concentration-sensitive agent-based model to simulate mouse behavior. This model provided evidence for a binaral-sniffing strategy (inter-nostril comparison of concentration in a single sniff) and a serial-sniffing strategy (sampling concentration, moving in space, and then sampling again). Serial-sniffing may be accomplished at farther distances by moving the body and at closer distances by moving the head (casting). Together, these results elucidate components of behavioral strategies for odor-based navigation.