Insulin resistance and carotid intima-media thickness mediate the association between resting-state heart rate variability and executive function: A path modelling study

The connection between heart rate variability (HRV), neurological health, and cognition: A literature review

The heart and brain have bi-directional influences on each other, including autonomic regulation and hemodynamic connections. Heart rate variability (HRV) measures variation in beat-to-beat intervals. New findings about disorganized sinus rhythm (erratic rhythm, quantified as heart rate fragmentation, HRF) are discussed and suggest overestimation of autonomic activities in HRV changes, especially during aging or cardiovascular events. When excluding HRF, HRV is regulated via the central autonomic network (CAN). HRV acts as a proxy of autonomic activity and is associated with executive functions, decision-making, and emotional regulation in our health and wellbeing. Abnormal changes of HRV (e.g., decreased vagal functioning) are observed in various neurological conditions including mild cognitive impairments, dementia, mild traumatic brain injury, migraine, COVID-19, stroke, epilepsy, and psychological conditions (e.g., anxiety, stress, and schizophrenia). Efforts are needed to improve the dynamic and intriguing heart-brain interactions.

Unraveling the cognitive correlates of heart rate variability with the drift diffusion model

The Neurovisceral Integration Model posits a link between resting vagally mediated heart rate variability (vmHRV) and cognitive control. Empirical support for this link is mixed, potentially due to coarse performance metrics such as mean response time (RT). To clarify this issue, we tested the relationships between resting vmHRV and refined estimates of cognitive control- as revealed by the ex-Gaussian model of RT and, to a greater extent, the drift diffusion model (DDM, a computational model of two-choice performance). Participants (N = 174) completed a five-minute resting baseline while ECG was collected followed by a Simon spatial conflict task. The root mean square of successive differences in interbeat intervals was calculated to index resting vmHRV. Resting vmHRV was unrelated to Simon's mean RT and accuracy rates, but was inversely related to the ex-Gaussian parameter reflecting slow RTs (tau); however, this finding was attenuated after adjustment for covariates. High resting vmHRV was related to faster drift rates and slower non-decision times, DDM parameters reflecting goal-directed cognition and sensorimotor processes, respectively. The DDM effects survived covariate adjustment and were specific to incongruent trials (i.e., when cognitive control demands were high). Findings suggest a link between vmHRV and cognitive control vis-a-vis drift rate, and potentially, a link between vmHRV and motoric inhibition vis-a-vis non-decision time. These cognitive correlates would have been missed with reliance on traditional performance. Findings are discussed with respect to the inhibitory processes that promote effective performance in high vmHRV individuals.

Intima Media Thickness and Cognitive Function Among Adults: Meta-Analysis of Observational and Longitudinal Studies

Background

Carotid structural changes measured by intima media thickness (IMT) have been related to cognitive complaints during aging. Therefore, the aims of this meta‐analysis were (1) to elucidate the relationship between vascular status, measured as IMT, and cognitive domains distinguishing between global cognition, executive functions, memory and attention; and (2) to explore whether demographic (ie, age and sex), clinical (ie, body mass index and IMT baseline values), and procedure characteristics influence this association.

Methods and Results

We performed a systematic review of MEDLINE (via PubMed), Scopus, and Web of Science databases from their inception to June 2021. Studies meeting the following inclusion criteria were included: (1) the participants were adults; (2) the exposure was carotid IMT; (3) the outcome was cognitive function, including global cognition, executive function, memory, and attention measured using standardized tests; and (4) the study design was cross‐sectional or longitudinal including unadjusted and adjusted analyses. A total of 19 cross‐sectional and 15 longitudinal studies were included and demographic (age and sex), clinical (body mass index and baseline IMT values), and procedure characteristics were analyzed as potential mediator or moderators of the association.

Conclusions

Our data support negative associations between IMT and cognitive function in cross‐sectional studies. The association between IMT and cognition lost significance in longitudinal studies and when controlling for covariates in cross‐sectional studies. Finally, the strength of these associations seems not to be modified by age, sex, body mass index, and baseline IMT values. This systematic review and meta‐analysis adds to the evidence supporting the use of IMT as a measure for identifying patients at risk of cognitive decline.

Sex-Specific Association of Endogenous PCSK9 With Memory Function in Elderly Subjects at High Cardiovascular Risk

Background: Growing evidence indicates that cognitive decline and cardiovascular diseases (CVDs) share common vascular risk factors. Protease proprotein convertase subtilisin/kexin type 9 (PCSK9) is associated with CV disease risk and has been also involved in neuronal differentiation.

Aim: Evaluate whether in patients at high CV risk cognitive function is related to PCSK9 levels.

Methods. One hundred sixty-six patients (67 female) were enrolled. A detailed neuropsychological (NP) assessment was performed. PCSK9 levels were measured with ELISA.

Results: Men had significantly higher short-term memory, executive function, and praxic and mental representation skills, as reflected by Forward Digit Span (FDS) (p = 0.005), Trail Making Test-A (TMT-A) (p = 0.047), Clock Drawing Test (CDT) (0.016). Endogenous PCSK9 levels were higher in female (p = 0.005). On linear regression analysis PCSK9 predicts short term memory only in females (Beta = 0.408, p = 0.001), with an interaction between PCSK9 and gender (p = 0.004 for interaction PCSK9 by sex). The association of PCSK9 with FDS in female was partially mediated by waist circumference (mediation effect 8.5%).

Conclusions: In patients at high CV risk short term memory was directly related to PCSK9 levels only in women, revealing the relevance of sex in this relationship. The association of PCSK9 with memory function may be mediated, at least in part, by waist circumference.

Autonomic function in amnestic and non-amnestic mild cognitive impairment: spectral heart rate variability analysis provides evidence for a brain-heart axis

Mild cognitive impairment (MCI) is a heterogeneous syndrome with two main clinical subtypes, amnestic (aMCI) and non-amnestic (naMCI). The analysis of heart rate variability (HRV) is a tool to assess autonomic function. Cognitive and autonomic processes are linked via the central autonomic network. Autonomic dysfunction entails several adverse outcomes. However, very few studies have investigated autonomic function in MCI and none have considered MCI subtypes or the relationship of HRV indices with different cognitive domains and structural brain damage. We assessed autonomic function during an active orthostatic challenge in 253 oupatients aged ≥ 65, [n = 82 aMCI, n = 93 naMCI, n = 78 cognitively normal (CN), neuropsychologically tested] with power spectral analysis of HRV. We used visual rating scales to grade cerebrovascular burden and hippocampal/insular atrophy (HA/IA) on neuroimaging. Only aMCI showed a blunted response to orthostasis. Postural changes in normalised low frequency (LF) power and in the LF to high frequency ratio correlated with a memory test (positively) and HA/IA (negatively) in aMCI, and with attention/executive function tests (negatively) and cerebrovascular burden (positively) in naMCI. These results substantiate the view that the ANS is differentially impaired in aMCI and naMCI, consistently with the neuroanatomic substrate of Alzheimer's and small-vessel subcortical ischaemic disease.

Heart Rate Variability is Associated with Memory in Females

Research into the association between heart rate variability (HRV) and cognitive function is scarce, particularly with regard to gender differences. HRV in 182 healthy volunteers was assessed by the root mean square of the successive difference (RMSSD) and spectrum analysis, while the Wechsler Memory Scale-Revised (WMS-R) was used to determine memory function. Robust and significant associations were found to exist between HRV (RMSSD and high-frequency HRV) and domains of the WMS-R in females. Caution should therefore be taken to control for gender when conducting studies on the relationships between HRV and cognitive variables.

The neuroscience of sadness: A multidisciplinary synthesis and collaborative review

Sadness is typically characterized by raised inner eyebrows, lowered corners of the mouth, reduced walking speed, and slumped posture. Ancient subcortical circuitry provides a neuroanatomical foundation, extending from dorsal periaqueductal grey to subgenual anterior cingulate, the latter of which is now a treatment target in disorders of sadness. Electrophysiological studies further emphasize a role for reduced left relative to right frontal asymmetry in sadness, underpinning interest in the transcranial stimulation of left dorsolateral prefrontal cortex as an antidepressant target. Neuroimaging studies - including meta-analyses - indicate that sadness is associated with reduced cortical activation, which may contribute to reduced parasympathetic inhibitory control over medullary cardioacceleratory circuits. Reduced cardiac control may - in part - contribute to epidemiological reports of reduced life expectancy in affective disorders, effects equivalent to heavy smoking. We suggest that the field may be moving toward a theoretical consensus, in which different models relating to basic emotion theory and psychological constructionism may be considered as complementary, working at different levels of the phylogenetic hierarchy.

The association between individual differences in executive functioning and resting high-frequency heart rate variability

Both resting high-frequency heart rate variability (HF-HRV) and executive functioning (EF) are individual differences implicated in vulnerability to a wide range of adverse outcomes. The overlapping set of associations, along with theoretical models positing connections between the brain regions subserving the executive functions and the parasympathetic nervous system, suggest that the two factors should be correlated. Seeking to address limitations in prior research, the current study examined the association between EF, measured comprehensively with individually-administered neuropsychological tests and controlling for lower-order cognitive processes, and resting physiology, measured with impedence cardiography, in healthy, community participants (68% female; mean age = 27, SD = 6.5). Results confirmed a significant association between EF and resting HF-HRV, but no association with resting state sympathetic nervous system activation (pre-ejection period). These findings may inform future investigation of transdiagnostic mechanisms related to these two individual difference factors.

Resting Heart Rate Variability Predicts Inhibitory Control Above and Beyond Impulsivity

Abstract. Heart rate variability (HRV) has been linked to effective functioning of prefrontal-subcortical inhibitory circuits. Despite the recognized role of the prefrontal cortex (PFC) in executive functions linked to inhibitory capacity, studies linking HRV to executive functions are inconsistent, likely due to potential confounders. The present study sought to examine this relation in a sample of 50 healthy participants (31 females; Mage = 24.2 years) who underwent assessment of resting HRV and two executive tasks assessing inhibitory control, namely the Rule Shift Cards and the Hayling Sentence Completion Test. Hierarchical multiple regressions showed that HRV predicted performance on both tasks (i.e., time taken to inhibit a strongly activated response) above and beyond the role of sex, body mass index, and impulsivity. Present results disconfirm that the HRV-executive function association is only due to confounders, and corroborate such relationship with the use of two ecological tasks assessing inhibitory control. Current findings support the Neurovisceral Integration Model and provide plausible explanation for previous inconsistent results.

Heart-rate variability: a biomarker to study the influence of nutrition on physiological and psychological health?

As the influence of diet on health may take place over a period of decades, there is a need for biomarkers that help to identify those aspects of nutrition that have either a positive or a negative influence. The evidence is considered that heart-rate variability (HRV) (the time differences between one beat and the next) can be used to indicate the potential health benefits of food items. Reduced HRV is associated with the development of numerous conditions for example, diabetes, cardiovascular disease, inflammation, obesity and psychiatric disorders. Although more systematic research is required, various aspects of diet have been shown to benefit HRV acutely and in the longer term. Examples include a Mediterranean diet, omega-3 fatty acids, B-vitamins, probiotics, polyphenols and weight loss. Aspects of diet that are viewed as undesirable, for example high intakes of saturated or trans-fat and high glycaemic carbohydrates, have been found to reduce HRV. It is argued that the consistent relationship between HRV, health and morbidity supports the view that HRV has the potential to become a widely used biomarker when considering the influence of diet on mental and physical health.

Heart rate variability in patients with bipolar disorder: From mania to euthymia

Bipolar Disorder (BD) is characterized by the occurrence of mania alternating with euthymia. The aim of the present study was to investigate the impact of BD on the autonomic nervous system, as indicated by heart rate variability (HRV). The study was registered in the Clinical Trials Registration (NCT01272518). Nineteen hospitalized, male patients (age: 34.0 ± 12.3 years) with type I BD were assessed during mania and at discharge on euthymia. HRV data were collected during 20- minutes in supine position at rest, on spontaneous breathing, using the Polar RS 800 CX frequencymeter. HRV measures included variables in time, frequency and non-linear domains. Psychiatric conditions were evaluated by the Mini International Neuropsychiatric Interview (MINI) and the Bech-Rafaelsen mania scale (BRMS). Time domain measures of RMSSD (Cohen's d = 0.668) and pNN50 (Cohen's d = 0.688) increased from first to second assessments. The high-frequency component (HFms2) also increased (Cohen's d = 0.586), while the LF/HF ratio decreased (Cohen's d = 0.785). Non-linear domain measures including the SD1 component (Cohen's d = 0.668), and the SD1/SD2 ratio (Cohen's d = 1.2934) extracted from the Poincare plot analysis increased from first to second assessment. The variables Lmean (Cohen's d = 0.9627), Lmax (Cohen's d = 1.2164), REC% (Cohen's d = 1.0595) and EntShannon (Cohen's d = 1.0607) were higher in mania. By contrast, ApEn (Cohen's d = 0.995) and EntSample (Cohen's d = 1.189) were less during mania, all reflecting ANS improvement. Findings are interpreted in the context of recently published models relating to neurovisceral integration across the continuum of time, and the implications for the future health and wellbeing of patients are considered.

Carotid intima-media thickness in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil): a narrative review

BACKGROUND

Carotid intima-media thickness (CIMT), as measured by ultrasound, has been used in large studies as a non-invasive marker for subclinical atherosclerosis. The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) is a cohort of 15,105 civil servants in six Brazilian cities that included CIMT evaluation in its baseline assessment. The aim of the present narrative review was to provide an overview of ELSA-Brasil CIMT articles published up to July 31, 2017.

DESIGN AND SETTING

Narrative review of ELSA-Brasil CIMT studies using baseline assessment data.

METHODS

We searched PubMed for the terms "ELSA-Brasil" and "intima-media". This search yielded 21 published articles using CIMT data from the ELSA-Brasil baseline assessment, which were included in this review. We also present information about intima-media thickness assessment from ongoing onsite reevaluations of the study participants.

RESULTS

Most published studies focused on the association with traditional and novel cardiovascular risk factors. Studies also presented information about the ELSA-Brasil CIMT protocol at baseline and CIMT value distribution in this large sample.

CONCLUSIONS

Analyses on the ELSA-Brasil data led to important insights on CIMT interpretation and physiology. Besides the highlighted contributions which have already been made in this field, new data gathered during the ongoing third onsite assessment will enable investigation of substantially new research questions.

Cortical thickness is associated with altered autonomic function in cognitively impaired and non-impaired older adults

KEY POINTS

The parasympathetic nervous system (PNS) is critical for adaptation to environment demands. Alzheimer's disease (AD), via frontal compensatory processes, may affect PNS regulation, thereby compromising older adults' capacity for adaptation, and increasing morbidity and mortality risk. Here we found that AD-associated neurodegeneration accompanied an overactive anterior cingulate cortex, which in turn resulted in a high level of PNS activity at rest, as well as strong PNS activity withdrawal in response to the mental effort. This discovery provides the first line of evidence to suggest that AD-associated neurodegeneration links to altered PNS regulation during mental effort in older adults, and that the compensatory processes accompanying frontal hyperactivation appear to be responsible for these alterations.

ABSTRACT

The parasympathetic nervous system (PNS) is critical for adaptation to environment demands. PNS can reflect an individual's regulatory capacity of frontal brain regions and has been linked to cognitive capacity. Yet, the relationship of PNS function to cognitive decline and abnormal frontal function that characterize preclinical progression toward Alzheimer's disease (AD) is unclear. Here, we aimed to elucidate the relationship between PNS function and AD-associated neurodegeneration by testing two competing hypotheses involving frontal regions' activity (neurodegeneration vs. compensation). In 38 older human adults with amnestic mild cognitive impairment (aMCI) or normative cognition, we measured AD-associated neurodegeneration (AD signature cortical thickness; ADSCT), resting-state functional magnetic resonance imaging of frontal regions' spontaneous activation, and an electrocardiography measure of PNS (high frequency heart rate variability; HF-HRV). HF-HRV was assessed at rest and during a cognitive task protocol designed to capture HF-HRV reactivity. Higher HF-HRV at rest was significantly related to both more severe AD-associated neurodegeneration (lower ADSCT scores) and worse cognitive ability. Cognitive impairments were also related to greater suppression of HF-HRV reactivity. High activities of the anterior cingulate cortex significantly mediated relationships between ADSCT and both HF-HRV at rest and HF-HRV reactivity. Notably, these relationships were not affected by the clinical phenotype. We show that AD-associated neurodegeneration is associated with altered PNS regulation and that compensatory processes linked to frontal overactivation might be responsible for those alterations. This finding provides the first line of evidence in a new framework for understanding how early-stage AD-associated neurodegeneration affects autonomic regulation.

From psychological moments to mortality: A multidisciplinary synthesis on heart rate variability spanning the continuum of time

Heart rate variability (HRV) indexes functioning of the vagus nerve, arguably the most important nerve in the human body. The Neurovisceral Integration Model has provided a structural framework for understanding brain-body integration, highlighting the role of the vagus in adaptation to the environment. In the present paper, we emphasise a temporal framework in which HRV may be considered a missing, structural link between psychological moments and mortality, a proposal we label as Neurovisceral Integration Across a Continuum of Time (or NIACT). This new framework places neurovisceral integration on a dimension of time, highlighting implications for lifespan development and healthy aging, and helping to bridge the gap between clearly demarcated disciplines such as psychology and epidemiology. The NIACT provides a novel framework, which conceptualizes how everyday psychological moments both affect and are affected by the vagus in ways that have long-term effects on mortality risk. We further emphasize that a longitudinal approach to understanding change in vagal function over time may yield novel scientific insights and important public health outcomes.

Relationship between Cognitive and Sleep-wake Variables in Asymptomatic Offspring of Patients with Late-onset Alzheimer's Disease

Early neuropathological changes characteristic of late-onset Alzheimer's disease (LOAD) involve brain stem and limbic structures that regulate neurovegetative functions, including sleep-wake rhythm. Indeed, sleep pattern is an emerging biomarker and a potential pathophysiological mechanism in LOAD. We hypothesized that cognitively asymptomatic, middle-aged offspring of patients with LOAD (O-LOAD) would display a series of circadian rhythm abnormalities prior to the onset of objective cognitive alterations. We tested 31 children of patients with LOAD (O-LOAD) and 19 healthy individuals without family history of Alzheimer's disease (control subjects, CS) with basic tests of cognitive function, as well as actigraphy measures of sleep-wake rhythm, cardiac autonomic function, and bodily temperature. Unexpectedly, O-LOAD displayed subtle but significant deficits in verbal episodic memory (Rey Auditory Verbal Learning Test delayed recall 10.6 ± 0.4 vs. 8.6 ± 0.6, t = 4.97, df = 49, p < 0.01) and language (Weschler's vocabulary 51.4 ± 1.3 vs. 44.3 ± 1.5, t = 2.49, df = 49, p < 0.001) compared to CS, even though all participants had results within the clinically normal range. O-LOAD showed a phase-delayed rhythm of body temperature (2.56 ± 0.47 h vs. 3.8 ± 0.26 h, t = 2.48, df = 40, p = 0.031). Cognitive performance in O-LOAD was associated with a series of cardiac autonomic sleep-wake variables; specifically indicators of greater sympathetic activity at night were related to poorer cognition. The present results suggest sleep pattern deserves further study as a potential neurobiological signature in LOAD, even in middle-aged, at risk individuals.