Forebrain neurocircuitry associated with human reflex cardiovascular control

Brain gray matter changes in children at risk for sudden unexpected death in epilepsy

BACKGROUND

Potential failing adult brain sites, stratified by risk, mediating Sudden Unexpected Death in Epilepsy (SUDEP) have been described, but are unknown in children.

METHODS

We examined regional brain volumes using T1-weighted MRI images in 21 children with epilepsy at high SUDEP risk and 62 healthy children, together with SUDEP risk scores, calculated from focal seizure frequency. Gray matter tissue type was partitioned, maps normalized, smoothed, and compared between groups (SPM12; ANCOVA; covariates, age, sex, and BMI). Partial correlations between regional volumes and seizure frequency were examined (SPM12, covariates, age, sex, and BMI); 67% were at high risk for SUDEP.

RESULTS

The cerebellar cortex, hippocampus, amygdala, putamen, cingulate, thalamus, and para-hippocampal gyrus showed increased gray matter volumes in epilepsy, and decreased volumes in the posterior thalamus, lingual gyrus, and temporal cortices. The cingulate, insula, and putamen showed significant positive relationships with focal seizure frequency indices using whole-brain voxel-by-voxel partial correlations. Tissue volume changes in selected sites differed in direction from adults; particularly, cerebellar sites, key for hypotensive recovery, increased rather than adult declines.

CONCLUSION

The volume increases may represent expansion by inflammatory or other processes that, with sustained repetitive seizure discharge, lead to tissue volume declines described earlier in adults.

IMPACT

Children with epilepsy, who are at risk for Sudden Unexplained Death, show changes in brain volume that often differ in direction of change from adults at risk for SUDEP. Sites of volume change play significant roles in mediating breathing and blood pressure, and include areas that serve recovery from prolonged apnea and marked loss of blood pressure. The extent of volume changes correlated with focal seizure frequency. Although the underlying processes contributing to regional volume changes remain speculative, regions of tissue swelling in pediatric brain areas may represent transitory conditions that later lead to tissue loss in the adult condition.

Brain white matter changes and their associations with non-motor dysfunction in orthostatic hypotension in α-synucleinopathy: A NODDI study

BACKGROUND

The specific non-motor symptoms associated with α-synucleinopathies, including orthostatic hypotension (OH), cognitive impairment, and emotional abnormalities, have been a subject of ongoing controversy over the mechanisms underlying the development of a vicious cycle among them. The distinct structural alterations in white matter (WM) in patients with α-synucleinopathies experiencing OH, alongside their association with other non-motor symptoms, remain unexplored. This study employs axial diffusivity and density imaging (NODDI) to investigate WM damage specific to α-synucleinopathies with concurrent OH, delivering fresh evidence to supplement our understanding of the pathogenic mechanisms and pathological rationales behind the occurrence of a spectrum of non-motor functional impairments in α-synucleinopathies.

METHODS

This study recruited 49 individuals diagnosed with α-synucleinopathies, stratified into an α-OH group (n = 24) and an α-NOH group (without OH, n = 25). Additionally, 17 healthy controls were included for supine and standing blood pressure data collection, as well as neuropsychological assessments. Magnetic resonance imaging (MRI) was utilized for the calculation of NODDI parameters, and tract-based spatial statistics (TBSS) were employed to explore differential clusters. The fibers covered by these clusters were defined as regions of interest (ROI) for the extraction of NODDI parameter values and the analysis of their correlation with neuropsychological scores.

RESULTS

The TBSS analysis unveiled specific cerebral regions exhibiting disparities within the α-OH group as compared to both the α-NOH group and the healthy controls. These differences were evident in clusters that indicated a decrease in the acquisition of the neurite density index (NDI), a reduction in the orientation dispersion index (ODI), and an increase in the isotropic volume fraction (FISO) (p < 0.05). The extracted values from these ROIs demonstrated significant correlations with clinically assessed differences in supine and standing blood pressure, overall cognitive scores, and anxiety-depression ratings (p < 0.05).

CONCLUSION

Patients with α-synucleinopathies experiencing OH exhibit distinctive patterns of microstructural damage in the WM as revealed by the NODDI model, and there is a correlation with the onset and progression of non-motor functional impairments.

Hippocampus under Pressure: Molecular Mechanisms of Development of Cognitive Impairments in SHR Rats

Data from clinical trials and animal experiments demonstrate relationship between chronic hypertension and development of cognitive impairments. Here, we review structural and biochemical alterations in the hippocampus of SHR rats with genetic hypertension, which are used as a model of essential hypertension and vascular dementia. In addition to hypertension, dysfunction of the hypothalamic-pituitary-adrenal system observed in SHR rats already at an early age may be a key factor of changes in the hippocampus at the structural and molecular levels. Global changes at the body level, such as hypertension and neurohumoral dysfunction, are associated with the development of vascular pathology and impairment of the blood-brain barrier. Changes in multiple biochemical glucocorticoid-dependent processes in the hippocampus, including dysfunction of steroid hormones receptors, impairments of neurotransmitter systems, BDNF deficiency, oxidative stress, and neuroinflammation are accompanied by the structural alterations, such as cellular signs of neuroinflammation micro- and astrogliosis, impairments of neurogenesis in the subgranular neurogenic zone, and neurodegenerative processes at the level of synapses, axons, and dendrites up to the death of neurons. The consequence of this is dysfunction of hippocampus, a key structure of the limbic system necessary for cognitive functions. Taking into account the available results at various levels starting from the body and brain structure (hippocampus) levels to molecular one, we can confirm translational validity of SHR rats for modeling mechanisms of vascular dementia.

Electrical stimulation of the ventromedial prefrontal cortex modulates muscle sympathetic nerve activity and blood pressure

We recently showed that transcranial alternating current stimulation of the dorsolateral prefrontal cortex modulates spontaneous bursts of muscle sympathetic nerve activity, heart rate, and blood pressure (Sesa-Ashton G, Wong R, McCarthy B, Datta S, Henderson LA, Dawood T, Macefield VG. Stimulation of the dorsolateral prefrontal cortex modulates muscle sympathetic nerve activity and blood pressure in humans. Cereb Cortex Comm. 2022:3:2tgac017.). Stimulation was delivered between scalp electrodes placed over the nasion and electroencephalogram (EEG) electrode site F3 (left dorsolateral prefrontal cortex) or F4 (right dorsolateral prefrontal cortex), and therefore the current passed within the anatomical locations underlying the left and right ventromedial prefrontal cortices. Accordingly, we tested the hypothesis that stimulation of the left and right ventromedial prefrontal cortices would also modulate muscle sympathetic nerve activity, although we predicted that this would be weaker than that seen during dorsolateral prefrontal cortex stimulation. We further tested whether stimulation of the right ventromedial prefrontal cortices would cause greater modulation of muscle sympathetic nerve activity, than stimulation of the left ventromedial prefrontal cortices. In 11 individuals, muscle sympathetic nerve activity was recorded via microelectrodes inserted into the right common peroneal nerve, together with continuous blood pressure, electrocardiogram, and respiration. Stimulation was achieved using transcranial alternating current stimulation, +2 to -2 mA, 0.08 Hz, 100 cycles, applied between electrodes placed over the nasion, and EEG electrode site FP1, (left ventromedial prefrontal cortices) or FP2 (right ventromedial prefrontal cortices); for comparison, stimulation was also applied over F4 (right dorsolateral prefrontal cortex). Stimulation of all three cortical sites caused partial entrainment of muscle sympathetic nerve activity to the sinusoidal stimulation, together with modulation of blood pressure and heart rate. We found a significant fall in mean blood pressure of ~6 mmHg (P = 0.039) during stimulation of the left ventromedial prefrontal cortices, as compared with stimulation of the right. We have shown, for the first time, that transcranial alternating current stimulation of the ventromedial prefrontal cortices modulates muscle sympathetic nerve activity and blood pressure in awake humans at rest. However, it is unclear if this modulation occurred through the same brain pathways activated during transcranial alternating current stimulation of the dorsolateral prefrontal cortex.

Paroxysmal Sympathetic Hyperactivity in Stroke

OBJECTIVE

Paroxysmal sympathetic hyperactivity (PSH) is a life-threatening neurological emergency associated with severe brain injury. Stroke-related PSH, particularly post-aneurysmal subarachnoid hemorrhage (aSAH) PSH, has been relatively understudied and is often misdiagnosed as an aSAH-related hyperadrenergic crisis. This study aims to clarify the feature of stroke-related PSH.

METHODS

This study discusses the case of a patient with post-aSAH PSH and identifies 19 articles (25 cases) on stroke-related PSH by searching the PubMed database from 1980 to 2021.

RESULTS

In the total cohort, 15 (60.0%) patients were male and the average age was 40.1 ± 16.6 years. The primary diagnoses included intracranial hemorrhage (13 cases, 52.0%), cerebral infarction (7 cases, 28.0%), subarachnoid hemorrhage (4 cases, 16.0%), and intraventricular hemorrhage (1 case, 4.0%). The sites of stroke damage were predominantly the cerebral lobe (10 cases, 40.0%), basal ganglia (8 cases, 32.0%), and the pons (4 cases, 16.0%). The median time of PSH onset after admission was 5 (1-180) days. Most cases employed combination therapy with sedation drugs, beta-blockers, gabapentin, and clonidine. On the Glasgow Outcome Scale, outcomes included death (4 cases, 21.1%), vegetative state (2 cases, 10.5%), severe disability (7 cases, 36.8%), and in only one case (5.3%) was a good recovery noted.

CONCLUSIONS

The clinical features and treatment of post-aSAH PSH differed from those of aSAH-related hyperadrenergic crises. Early diagnosis and treatment can prevent severe complications. PSH should be acknowledged as a potential complication of aSAH. Differential diagnosis can aid in developing individualized treatment plans and improving patient prognosis.

Reduced cardiovagal baroreflex sensitivity is associated with postural orthostatic tachycardia syndrome (POTS) and pain chronification in patients with headache

Background

Non-cephalgic symptoms including orthostatic intolerance, fatigue, and cognitive impairment, are common in patients with chronic headache disorders and may result from alterations in the autonomic nervous system. However, little is known about the function of autonomic reflexes, which regulate cardiovascular homeostasis and cerebral perfusion in patients with headache.

Methods

Autonomic function testing data from patients with headache collected between January 2018 and April 2022 was retrospectively analyzed. Through review of EMR we determined headache pain chronicity and patient self-report of orthostatic intolerance, fatigue, and cognitive impairment. Composite Autonomic Severity Score (CASS), CASS subscale scores, and cardiovagal and adrenergic baroreflex sensitivities were used to quantify autonomic reflex dysfunction. Descriptive analyses (Mann-Whitney-U or χ2, as appropriate) determined associations between autonomic reflex dysfunction and POTS as well as chronic headache. Binomial logistic regression adjusted for age and sex. Spearman’s rank correlation determined the association between the total CASS score and the number of painless symptoms reported by each participant.

Results

We identified 34 patients meeting inclusion criteria, of whom there were 16 (47.0%) with orthostatic intolerance, 17 (50.0%) with fatigue, 11 (32.4%) with cognitive complaints, and 11 (32.4%) with Postural Orthostatic Tachycardia Syndrome (POTS). The majority of participants had migraine (n = 24, 70.6%), were female (n = 23, 67.6%) and had a chronic (&gt;15 headache days in a month) headache disorder (n = 26, 76.5%). Reduced cardiovagal baroreflex sensitivity (BRS-V) independently predicted chronic headache [aOR: 18.59 (1.16, 297.05), p = 0.039] and POTS [aOR: 5.78 (1.0, 32.5), p = 0.047]. The total CASS was correlated with the total number of non-painful features in the expected direction (r = 0.46, p = 0.007).

Conclusion

Abnormal autonomic reflexes may play an important role in pain chronification and the development of POTS in patients with headache.

Exploring the brain with sleep-related injuries, and fixing it

The focus of my research efforts rests with determining dysfunctional neural systems underlying disorders of sleep, and identifying interventions to overcome those disorders. Aberrant central and physiological control during sleep exerts serious consequences, including disruptions in breathing, motor control, blood pressure, mood, and cognition, and plays a major role in sudden infant death syndrome, congenital central hypoventilation, and sudden unexpected death in epilepsy, among other concerns. The disruptions can be traced to brain structural injury, leading to inappropriate outcomes. Identification of failing systems arose from the assessment of single neuron discharge in intact, freely moving and state-changing human and animal preparations within multiple systems, including serotonergic action and motor control sites. Optical imaging of chemosensitive, blood pressure and other breathing regulatory areas, especially during development, were useful to show integration of regional cellular action in modifying neural output. Identification of damaged neural sites in control and afflicted humans through structural and functional magnetic resonance imaging procedures helped to identify the sources of injury, and the nature of interactions between brain sites that compromise physiological systems and lead to failure. Interventions to overcome flawed regulatory processes were developed, and incorporate noninvasive neuromodulatory means to recruit ancient reflexes or provide peripheral sensory stimulation to assist breathing drive to overcome apnea, reduce the frequency of seizures, and support blood pressure in conditions where a failure to perfuse can lead to death.

The Effects of Respiratory Muscle Training on Resting-State Brain Activity and Thoracic Mobility in Healthy Subjects: A Randomized Controlled Trial

BACKGROUND

Although inspiratory muscle training (IMT) is an effective intervention for improving breath perception, brain mechanisms have not been studied yet.

PURPOSE

To examine the effects of IMT on insula and default mode network (DMN) using resting-state functional MRI (RS-fMRI).

STUDY TYPE

Prospective.

POPULATION

A total of 26 healthy participants were randomly assigned to two groups as IMT group (n = 14) and sham IMT groups (n = 12).

FIELD STRENGTH/SEQUENCE

A 3-T, three-dimensional T2* gradient-echo echo planar imaging sequence for RS-fMRI was obtained.

ASSESSMENT

The intervention group received IMT at 60% and sham group received at 15% of maximal inspiratory pressure (MIP) for 8 weeks. Pulmonary and respiratory muscle function, and breathing patterns were measured. Groups underwent RS-fMRI before and after the treatment.

STATISTICAL TESTS

Statistical tests were two-tailed P < 0.05 was considered statistically significant. Student's t test was used to compare the groups. One-sample t-test for each group was used to reveal pattern of functional connectivity. A statistical threshold of P < 0.001 uncorrected value was set at voxel level. We used False discovery rate (FDR)-corrected P < 0.05 cluster level.

RESULTS

The IMT group showed more prominent alterations in insula and DMN connectivity than sham group. The MIP was significantly different after IMT. Respiratory rate (P = 0.344), inspiratory time (P = 0.222), expiratory time (P = 1.000), and inspiratory time/total breath time (P = 0.572) of respiratory patterns showed no significant change after IMT. All DMN components showed decreased, while insula showed increased activation significantly.

DATA CONCLUSION

Differences in brain activity and connectivity may reflect improved ventilatory perception with IMT with a possible role in regulating breathing pattern by processing interoceptive signals.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 4.

A recent suicide attempt and the heartbeat: Electrophysiological findings from a trans-diagnostic cohort of patients and healthy controls

Suicidal behavior is influenced by a multitude of factors, making prediction and prevention of suicide attempts (SA) a challenge. A useful tool to uncover underlying pathophysiology or propose new therapy approaches are biomarkers, especially within the context of point-of-care tests. Heart rate variability (HRV) is a well-established biomarker of mental health, and measures the activity of the sympathetic and parasympathetic nervous system (PNS). Previous studies reported a correlation between lower PNS activity and suicidality. However, most studies involved participants from a healthy population, patients without history of suicide attempts, or patients with a single diagnosis. 52 in-patients with a recent suicide attempt (<6 months), and 43 controls without history of SA or psychiatric diagnoses confirmed study participation. The included patients age ranged between 18 and 65 years, 65% had psychiatric comorbidities. Patients with dementia, cognitive impairments, acute psychosis, chronic non suicidal self-harming behavior, or current electroconvulsive therapy were excluded. A 15-min resting state electrocardiography was recorded with two bipolar electrodes attached to the right and left insides of the wrists. The multiple regression analyses showed lower parasympathetic, and higher sympathetic activity in patients compared to controls. Partial correlation found a positive trend result between self-reported suicidality and the very low frequency band. ROC curve analysis revealed an acceptable to excellent clinical accuracy of HRV parameters. Therefore, HRV parameters could be reliable discriminative biomarkers between in-patients with a recent SA and healthy controls. One limitation is the lack of a control group consisting of in-patients without life-time suicidal ideation or attempts.

Brain and cardiovascular-related changes are associated with aging, hypertension, and atrial fibrillation

PURPOSE

The neural pathways in which the brain regulates the cardiovascular system is via sympathetic and parasympathetic control of the heart and sympathetic control of the systemic vasculature. Various cortical and sub-cortical sites are involved, but how these critical brain regions for cardiovascular control are altered in healthy aging and other risk conditions that may contribute to cardiovascular disease is uncertain.

METHODS

Here we review the functional and structural brain changes in healthy aging, hypertension, and atrial fibrillation - noting their potential influence on the autonomic nervous system and hence on cardiovascular control.

RESULTS

Evidence suggests that aging, hypertension, and atrial fibrillation are each associated with functional and structural changes in specific areas of the central nervous system involved in autonomic control. Increased muscle sympathetic nerve activity (MSNA) and significant alterations in the brain regions involved in the default mode network are commonly reported in aging, hypertension, and atrial fibrillation.

CONCLUSIONS

Further studies using functional and structural magnetic resonance imaging (MRI) coupled with autonomic nerve activity in healthy aging, hypertension, and atrial fibrillation promise to reveal the underlying brain circuitry modulating the abnormal sympathetic nerve activity in these conditions. This understanding will guide future therapies to rectify dysregulation of autonomic and cardiovascular control by the brain.

The neurobiology of childhood trauma-aldosterone and blood pressure changes in a community sample

OBJECTIVE

Childhood trauma is an important risk factor for the onset and course of psychiatric disorders and particularly major depression. Recently, the renin-angiotensin-aldosterone system, one of the core stress hormone systems, has been demonstrated to be modified by childhood trauma.

METHODS

Childhood trauma was obtained using the Childhood Trauma Questionnaire (CTQ) in a community-dwelling sample (N = 2038). Plasma concentrations of renin and aldosterone were measured in subjects with childhood trauma (CT; N = 385) vs. subjects without this experience (NoCT; N = 1653). Multivariable linear regression models were calculated to assess the associations between CTQ, systolic and diastolic blood pressure, renin and aldosterone concentrations, and the ratio of aldosterone and systolic blood pressure (A/SBP).

RESULTS

CT subjects demonstrated higher plasma aldosterone (A) concentrations, a lower systolic and diastolic blood pressure, and a higher A/SBP. In addition, both aldosterone concentrations, as well as A/SBP, correlated with the severity of childhood trauma. These findings could not be attributed to differences in concomitant medication.

CONCLUSIONS

In conclusion, childhood trauma was associated with neurobiological markers, which may impact the risk for psychiatric disorders, primarily major depression. The altered A/SBP ratio points to a desensitisation of peripheral mineralocorticoid receptor function, which may be a target for therapeutic interventions.

Regional variation in brain tissue texture in patients with tonic-clonic seizures

Patients with epilepsy, who later succumb to sudden unexpected death, show altered brain tissue volumes in selected regions. It is unclear whether the alterations in brain tissue volume represent changes in neurons or glial properties, since volumetric procedures have limited sensitivity to assess the source of volume changes (e.g., neuronal loss or glial cell swelling). We assessed a measure, entropy, which can determine tissue homogeneity by evaluating tissue randomness, and thus, shows tissue integrity; the measure is easily calculated from T1-weighted images. T1-weighted images were collected with a 3.0-Tesla MRI from 53 patients with tonic-clonic (TC) seizures and 53 healthy controls; images were bias-corrected, entropy maps calculated, normalized to a common space, smoothed, and compared between groups (TC patients and controls using ANCOVA; covariates, age and sex; SPM12, family-wise error correction for multiple comparisons, p<0.01). Decreased entropy, indicative of increased tissue homogeneity, appeared in major autonomic (ventromedial prefrontal cortex, hippocampus, dorsal and ventral medulla, deep cerebellar nuclei), motor (sensory and motor cortex), or both motor and autonomic regulatory sites (basal-ganglia, ventral-basal cerebellum), and external surfaces of the pons. The anterior and posterior thalamus and midbrain also showed entropy declines. Only a few isolated regions showed increased entropy. Among the spared autonomic regions was the anterior cingulate and anterior insula; the posterior insula and cingulate were, however, affected. The entropy alterations overlapped areas of tissue changes found earlier with volumetric measures, but were more extensive, and indicate widespread injury to tissue within critical autonomic and breathing regulatory areas, as well as prominent damage to more-rostral sites that exert influences on both breathing and cardiovascular regulation. The entropy measures provide easily-collected supplementary information using only T1-weighted images, showing aspects of tissue integrity other than volume change that are important for assessing function.

Baroreflex sensitivity during rest and pressor challenges in obstructive sleep apnea patients with and without CPAP

INTRODUCTION

Obstructive sleep apnea (OSA) increases sympathetic vasoconstrictor drive and reduces baroreflex sensitivity (BRS), the degree to which blood pressure changes modify cardiac output. Whether nighttime continuous positive airway pressure (CPAP) corrects BRS in the awake state in OSA remains unclear. We assessed spontaneous BRS using non-invasive continuous BP and ECG recordings at rest and during handgrip and Valsalva challenges, maneuvers that increase vasoconstrictor drive with progressively higher BP, in untreated OSA (unOSA), CPAP-treated OSA (cpOSA) and healthy (CON) participants.

METHODS

In a cross-sectional study of 104 participants, 34 unOSA (age mean±std, 50.6±14.1years; Respiratory Event Index [REI] 21.0±15.3 events/hour; 22male), 31 cpOSA (49.6±14.5years; REI 23.0±14.2 events/hour; 22male; self-report 4+hours/night,5+days/week,6months), and 39 CON (42.2±15.0years; 17male), we calculated BRS at rest and during handgrip and Valsalva. Additionally, we correlated BP variability (BPV) with BRS during these protocols.

RESULTS

BRS in unOSA, cpOSA and CON was, respectively (mean±sdv in ms/mmHg), at rest: 14.8±11.8, 15.8±17.0, 16.1±11.3; during handgrip 13.3±7.6, 12.7±8.4, 16.4±8.7; and during Valsalva 12.7±8.0, 11.5±6.6, 15.1±8.9. BRS was lower in cpOSA than CON for handgrip (p=0.04) and Valsalva (p=0.03). BRS was negatively correlated with BPV in unOSA during Valsalva and handgrip for cpOSA, both R=-0.4 (p=0.02). BRS was negatively correlated with OSA severity (levels: none, mild, moderate, severe) at R=-0.2 (p=0.04,n=104).

CONCLUSIONS

As expected, BRS was lower and BPV higher in OSA during the pressor challenges, and disease severity negatively correlated with BRS. In this cross-sectional study, both CPAP-treated (self-reported) and untreated OSA showed reduced BRS, leaving open whether within-person CPAP improves BRS.

Brain Neural Underpinnings of Interoception and Decision-Making in Alzheimer's Disease: A Narrative Review

This study reviews recent literature on interoception directing decision-making in Alzheimer's disease (AD). According to the somatic marker hypothesis, signals from the internal body direct decision-making and involve the ventromedial prefrontal cortex (vmPFC). After reviewing relevant studies, we summarize the brain areas related to interoception and decision-making (e.g., vmPFC, hippocampus, amygdala, hypothalamus, anterior cingulate cortex, and insular cortex) and their roles in and relationships with AD pathology. Moreover, we outline the relationship among interoception, the autonomic nervous system, endocrine system, and AD pathology. We discuss that impaired interoception leads to decreased decision-making ability in people with AD from the perspective of brain neural underpinning. Additionally, we emphasize that anosognosia or reduced self-awareness and metacognition in AD are remarkably congruent with the malfunction of the autonomic nervous system regulating the interoceptive network. Furthermore, we propose that impaired interoception may contribute to a loss in the decision-making ability of patients with AD. However, there still exist empirical challenges in confirming this proposal. First, there has been no standardization for measuring or improving interoception to enhance decision-making ability in patients with AD. Future studies are required to better understand how AD pathology induces impairments in interoception and decision-making.

Leveraging Continuous Vital Sign Measurements for Real-Time Assessment of Autonomic Nervous System Dysfunction After Brain Injury: A Narrative Review of Current and Future Applications

Subtle and profound changes in autonomic nervous system (ANS) function affecting sympathetic and parasympathetic homeostasis occur as a result of critical illness. Changes in ANS function are particularly salient in neurocritical illness, when direct structural and functional perturbations to autonomic network pathways occur and may herald impending clinical deterioration or intervenable evolving mechanisms of secondary injury. Sympathetic and parasympathetic balance can be measured quantitatively at the bedside using multiple methods, most readily by extracting data from electrocardiographic or photoplethysmography waveforms. Work from our group and others has demonstrated that data-analytic techniques can identify quantitative physiologic changes that precede clinical detection of meaningful events, and therefore may provide an important window for time-sensitive therapies. Here, we review data-analytic approaches to measuring ANS dysfunction from routine bedside physiologic data streams and integrating this data into multimodal machine learning-based model development to better understand phenotypical expression of pathophysiologic mechanisms and perhaps even serve as early detection signals. Attention will be given to examples from our work in acute traumatic brain injury on detection and monitoring of paroxysmal sympathetic hyperactivity and prediction of neurologic deterioration, and in large hemispheric infarction on prediction of malignant cerebral edema. We also discuss future clinical applications and data-analytic challenges and future directions.

Neurophysiologic Reactions during Heart Rate Variability Biofeedback Session in Adolescents with Different Risk of Internet Addiction

The aim of this study was to determine electroencephalogram (EEG) in a session of heart rate variability biofeedback (HRV BF) in adolescents with different Internet addiction (IA) risks. In total, 100 healthy adolescents aged 16–17 years with minimal risk of IA (Group I, 35%), pronounced risk of IA (Group II, 51%), and stable pattern of IA (Group III, 14%) using the Chen Internet Addiction Scale were examined. HRV and EEG parameters were determined at baseline (5 min), and then during the short-term HRV BF session (5 min), in order to increase the total power (TP, ms²) of the HRV spectrum. Against the background of an increase in the TP and a decrease in sympathetic activity, an increase in alpha EEG was revealed, especially in Groups I and II. The greatest increase in the power of beta₁-activity of EEG in the frontal, central, and temporal brain regionswas found in Groups I and II. In adolescents with a pronounced risk of IA, HRV BF is accompanied by a severe activation of the brain systems, while in persons with a stable type of IA, the least brain reactivity is shown, especially in the beta₁ EEG band.

Cortical–Hypothalamic Integration of Autonomic and Endocrine Stress Responses

The prevalence and severity of cardiovascular disease (CVD) are exacerbated by chronic stress exposure. While stress-induced sympathetic activity and elevated glucocorticoid secretion impair cardiovascular health, the mechanisms by which stress-responsive brain regions integrate autonomic and endocrine stress responses remain unclear. This review covers emerging literature on how specific cortical and hypothalamic nuclei regulate cardiovascular and neuroendocrine stress responses. We will also discuss the current understanding of the cellular and circuit mechanisms mediating physiological stress responses. Altogether, the reviewed literature highlights the current state of stress integration research, as well unanswered questions about the brain basis of CVD risk.

Brain structural and functional correlates to defense-related inhibition of muscle sympathetic nerve activity in man

An individual’s blood pressure (BP) reactivity to stress is linked to increased risk of hypertension and cardiovascular disease. However, inter- and intra-individual BP variability makes understanding the coupling between stress, BP reactivity, and long-term outcomes challenging. Previous microneurographic studies of sympathetic signaling to muscle vasculature (i.e. muscle sympathetic nerve activity, MSNA) have established a neural predictor for an individual’s BP reactivity during short-lasting stress. Unfortunately, this method is invasive, technically demanding, and time-consuming and thus not optimal for widespread use. Potential central nervous system correlates have not been investigated. We used MagnetoEncephaloGraphy and Magnetic Resonance Imaging to search for neural correlates to sympathetic response profiles within the central autonomic network and sensorimotor (Rolandic) regions in 20 healthy young males. The main correlates include (a) Rolandic beta rebound and an anterior cingulate cortex (ACC) response elicited by sudden stimulation and (b) cortical thickness in the ACC. Our findings highlight the involvement of the ACC in reactions to stress entailing peripheral sympathetic responses to environmental stimuli. The Rolandic response furthermore indicates a surprisingly strong link between somatosensory and autonomic processes. Our results thus demonstrate the potential in using non-invasive neuroimaging-based measures of stress-related MSNA reactions, previously assessed only using invasive microneurography.

Exploring physiologic reactions to persuasive information

Persuasion aims at changing peoples’ motivations and/or behaviors. This study explores how and when physiology reflects persuasion processes and specifically whether individual differences in motivations and behaviors affect psychophysiologic reactions to persuasive information. Participants (N = 70) with medium or high meat consumption patterns watched a persuasive video advocating limited meat consumption, while their electrodermal and cardiovascular physiology was measured. Results indicated that the video increased participants’ moral beliefs, perceived behavioral control, and reduction intentions. This study also found an increase in physiologic arousal during the persuasive video and that people with motivations less aligned to the persuasion objective had more physiologic arousal. The findings encourage further psychophysiologic persuasion research, especially as these insights can potentially be used to personalize persuasive messages of behavior change applications.

Persuasion consists of a diversity of mental processes that despite the efforts of many scholars are not fully understood. This explorative manuscript describes an important next step in using peripheral physiology to get information about persuasion‐related processes. It describes how and when people’s physiologic activity changes due to persuasion and what these changes might mean for the personalization of Persuasive Technologies.

Adverse childhood experiences (ACEs) relate to blunted cardiovascular and cortisol reactivity to acute laboratory stress: A systematic review and meta-analysis

Adverse childhood experiences (ACEs) are associated with poor future mental and physical health. Altered biological reactivity to mental stress may be a possible mechanism linking ACEs to poor health. However, it is not clear if ACEs relate to blunted or exaggerated stress reactivity. This meta-analysis aimed to determine whether exposure to ACEs is associated with cardiovascular and cortisol stress reactivity. A systematic review yielded 37 sources. Random-effects modelling tested the aggregate effects of 83 studies of the association between ACEs and stress reactivity. Exposure to ACEs was associated with relatively blunted cardiovascular and cortisol stress reactivity. Effect sizes did not vary as a function of sample sex or reactivity measure (e.g., heart rate, blood pressure, or cortisol). Meta-regression revealed preliminary evidence of greater blunting in samples of a younger age and samples reporting greater ACE exposure. Subgroup analyses for stress task, ACE measurement instrument, and sample race were not conducted because of a lack of between-study variability. Exposure to ACEs is associated with dysregulation of multiple components of the human stress response system.

Sympathetic Neural Control in Humans with Anxiety-Related Disorders

Numerous conceptual models are used to describe the dynamic responsiveness of physiological systems to environmental pressures, originating with Claude Bernard's milieu intérieur and extending to more recent models such as allostasis. The impact of stress and anxiety upon these regulatory processes has both basic science and clinical relevance, extending from the pioneering work of Hans Selye who advanced the concept that stress can significantly impact physiological health and function. Of particular interest within the current article, anxiety is independently associated with cardiovascular risk, yet mechanisms underlying these associations remain equivocal. This link between anxiety and cardiovascular risk is relevant given the high prevalence of anxiety in the general population, as well as its early age of onset. Chronically anxious populations, such as those with anxiety disorders (i.e., generalized anxiety disorder, panic disorder, specific phobias, etc.) offer a human model that interrogates the deleterious effects that chronic stress and allostatic load can have on the nervous system and cardiovascular function. Further, while many of these disorders do not appear to exhibit baseline alterations in sympathetic neural activity, reactivity to mental stress offers insights into applicable, real-world scenarios in which heightened sympathetic reactivity may predispose those individuals to elevated cardiovascular risk. This article also assesses behavioral and lifestyle modifications that have been shown to concurrently improve anxiety symptoms, as well as sympathetic control. Lastly, future directions of research will be discussed, with a focus on better integration of psychological factors within physiological studies examining anxiety and neural cardiovascular health. © 2022 American Physiological Society. Compr Physiol 12:1-33, 2022.

Heart Rate Variability Biofeedback Improves Emotional and Physical Health and Performance: A Systematic Review and Meta Analysis

We performed a systematic and meta analytic review of heart rate variability biofeedback (HRVB) for various symptoms and human functioning. We analyzed all problems addressed by HRVB and all outcome measures in all studies, whether or not relevant to the studied population, among randomly controlled studies. Targets included various biological and psychological problems and issues with athletic, cognitive, and artistic performance. Our initial review yielded 1868 papers, from which 58 met inclusion criteria. A significant small to moderate effect size was found favoring HRVB, which does not differ from that of other effective treatments. With a small number of studies for each, HRVB has the largest effect sizes for anxiety, depression, anger and athletic/artistic performance and the smallest effect sizes on PTSD, sleep and quality of life. We found no significant differences for number of treatment sessions or weeks between pretest and post-test, whether the outcome measure was targeted to the population, or year of publication. Effect sizes are larger in comparison to inactive than active control conditions although significant for both. HRVB improves symptoms and functioning in many areas, both in the normal and pathological ranges. It appears useful as a complementary treatment. Further research is needed to confirm its efficacy for particular applications.

Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation

OBJECTIVE

Fibroblast growth factor homologous factors (FHFs) are brain and cardiac sodium channel-binding proteins that modulate channel density and inactivation gating. A recurrent de novo gain-of-function missense mutation in the FHF1(FGF12) gene (p.Arg52His) is associated with early infantile epileptic encephalopathy 47 (EIEE47; Online Mendelian Inheritance in Man database 617166). To determine whether the FHF1 missense mutation is sufficient to cause EIEE and to establish an animal model for EIEE47, we sought to engineer this mutation into mice.

METHODS

The Arg52His mutation was introduced into fertilized eggs by CRISPR (clustered regularly interspaced short palindromic repeats) editing to generate Fhf1^{R52H /F+} mice. Spontaneous epileptiform events in Fhf1^{R52H /+} mice were assessed by cortical electroencephalography (EEG) and video monitoring. Basal heart rhythm and seizure-induced arrhythmia were recorded by electrocardiography. Modulation of cardiac sodium channel inactivation by FHF1B_R52H protein was assayed by voltage-clamp recordings of FHF-deficient mouse cardiomyocytes infected with adenoviruses expressing wild-type FHF1B or FHF1B_R52H protein.

RESULTS

All Fhf1^{R52H /+} mice experienced seizure or seizurelike episodes with lethal ending between 12 and 26 days of age. EEG recordings in 19-20-day-old mice confirmed sudden unexpected death in epilepsy (SUDEP) as severe tonic seizures immediately preceding loss of brain activity and death. Within 2-53 s after lethal seizure onset, heart rate abruptly declined from 572 ± 16 bpm to 108 ± 15 bpm, suggesting a parasympathetic surge accompanying seizures that may have contributed to SUDEP. Although ectopic overexpression of FHF1B_R52H in cardiomyocytes induced a 15-mV depolarizing shift in voltage of steady-state sodium channel inactivation and slowed the rate of channel inactivation, heart rhythm was normal in Fhf1^{R52H /+} mice prior to seizure.

SIGNIFICANCE

The Fhf1 missense mutation p.Arg52His induces epileptic encephalopathy with full penetrance in mice. Both Fhf1 (p.Arg52His) and Scn8a (p.Asn1768Asp) missense mutations enhance sodium channel Na_v 1.6 currents and induce SUDEP with bradycardia in mice, suggesting an FHF1/Na_v 1.6 functional axis underlying altered brain sodium channel gating in epileptic encephalopathy.

Admission Features Associated With Paroxysmal Sympathetic Hyperactivity After Traumatic Brain Injury: A Case-Control Study

OBJECTIVES

Paroxysmal sympathetic hyperactivity occurs in a subset of critically ill traumatic brain injury patients and has been associated with worse outcomes after traumatic brain injury. The goal of this study was to identify admission risk factors for the development of paroxysmal sympathetic hyperactivity in traumatic brain injury patients.

DESIGN

Retrospective case-control study of age- and Glasgow Coma Scale-matched traumatic brain injury patients.

SETTING

Neurotrauma ICU at the R. Adams Cowley Shock Trauma Center of the University of Maryland Medical System, January 2016 to July 2018.

PATIENTS

Critically ill adult traumatic brain injury patients who underwent inpatient monitoring for at least 14 days were included. Cases were identified based on treatment for paroxysmal sympathetic hyperactivity with institutional first-line therapies and were confirmed by retrospective tabulation of established paroxysmal sympathetic hyperactivity diagnostic and severity criteria. Cases were matched 1:1 by age and Glasgow Coma Scale to nonparoxysmal sympathetic hyperactivity traumatic brain injury controls, yielding 77 patients in each group.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Admission characteristics independently predictive of paroxysmal sympathetic hyperactivity included male sex, higher admission systolic blood pressure, and initial CT evidence of diffuse axonal injury, intraventricular hemorrhage/subarachnoid hemorrhage, complete cisternal effacement, and absence of contusion. Paroxysmal sympathetic hyperactivity cases demonstrated significantly worse neurologic outcomes upon hospital discharge despite being matched for injury severity at admission.

CONCLUSIONS

Several anatomical, epidemiologic, and physiologic risk factors for clinically relevant paroxysmal sympathetic hyperactivity can be identified on ICU admission. These features help characterize paroxysmal sympathetic hyperactivity as a clinical-pathophysiologic phenotype associated with worse outcomes after traumatic brain injury.

Neurobiological mechanisms of early life adversity, blunted stress reactivity and risk for addiction

Blunted stress reactivity resulting from early exposure to stress during childhood and adolescence may increase vulnerability to addiction. Early life adversity (ELA) affects brain structure and function and results in blunted stress axis reactivity. In this review, we focus on the underlying neurobiological mechanisms associated with a blunted response to stress, ELA, and risk for addictive disorders. ELA and blunted reactivity are accompanied by unstable mood regulation, impulsive behaviors, and reduced cognitive function. Neuroimaging studies reveal cortical and subcortical changes in persons exposed to ELA and those who have a genetic disposition for addiction. We propose a model in which blunted stress reactivity may be a marker of risk for addiction through an altered motivational and behavioral reactivity to stress that contribute to disinhibited behavioral reactivity and impulsivity leading in turn to increased vulnerability for substance use. Evidence supporting this hypothesis in the context of substance use initiation, maintenance, and risk for relapse is presented. The effects of ELA on persons at risk for addiction may lead to early experimentation with drugs of abuse. Early adoption of drug intake may alter neuroregulation in such vulnerable persons leading to a permanent dysregulation of motivational responses consistent with dependence. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.

Orthostatic Hypotension in Elderly Patients with Essential Tremor

PURPOSE

Essential tremor (ET) is the most common movement disorder in which dysautonomia symptoms can be present. We aimed to evaluate the presence of orthostatic hypotension (OH) and its relationship with the clinical features.

PATIENTS AND METHODS

Forty-four elderly patients with ET and 118 healthy elderly controls were included. OH was assessed via the head-up tilt table test and defined, according to the change in position, as a drop of at least 20 mmHg in systolic blood pressure and/or 10 mmHg in diastolic blood pressure. Tremor severity was evaluated using the Fahn-Tolosa-Marin Tremor Rating (FTMTR) Scale. All patients underwent geriatric comprehensive assessment.

RESULTS

There were no differences between the controls and patients with ET regarding age and gender. The mean age was 72.8±6.1, the mean disease duration 19.1±13.5 years and the mean FTMTR score was 30.9±17.1 in patients with ET. The frequency of OH at the 1st minute in patients with ET was higher than in controls (31.8% vs 17.8%, p=0.046). Furthermore, the frequency of jaw tremor in patients with OH was higher than in those without OH (35.7% vs 6.7%, p=0.025). About 28.6% of ET patients with OH had orthostatic symptoms.

CONCLUSION

We demonstrated that ET patients, particularly those with jaw tremors, had OH and that most of them were asymptomatic. Therefore, in order to protect patients from complications related to OH, it would be appropriate to evaluate OH in the follow-up and treatment of elderly patients with ET.

Action potential subpopulations within human muscle sympathetic nerve activity: Discharge properties and governing mechanisms

Sympathetic emissions directed towards the skeletal muscle circulation - muscle sympathetic nerve activity (MSNA) - represent a key mechanism for maintaining homeostasis and supporting human survival during physiological stress. Pulse-rhythmic bursts formed by the synchronous discharge of differently-sized sympathetic action potentials (APs) represent the primary characteristic of MSNA. Of the APs firing under baseline conditions (reflecting low-threshold c-fibre activity), a range of subpopulations exists, of which three general categories can be discussed based on their peak-to-peak amplitude in the filtered raw neurogram - small, medium, and large. These subpopulations express nonuniform discharge, recruitment, and synchronization patterns. The subpopulation of medium APs fires synchronously in most bursts, while the subpopulations of small and large APs fire less often. However, 30% of total AP discharge occurs asynchronously between sympathetic bursts, a pattern expressed most often by small APs. In response to physiological stress (e.g., baroreflex unloading), the subpopulation of medium APs exhibits the largest increase in firing probability and a subpopulation of previously-silent larger and faster-conducting APs (reflecting high-threshold c-fibre activity) becomes recruited. Heterogeneous discharge, synchronization, and recruitment thresholds among AP subpopulations stem from differential regulation within the sympathetic organization including the arterial baroreflex and paravertebral ganglia. Indeed, the arterial baroreflex strongly regulates medium APs at baseline and enhances its control over this subpopulation during periods of baroreflex unloading. Conversely, small and large APs express weak baroreflex control. Trimethaphan infusion has revealed that ganglionic processes including nicotinic and non-nicotinic mechanisms may contribute to heterogenous firing behaviours among low-threshold AP subpopulations. This review highlights recent work revealing new insight to the discharge properties expressed by, and mechanisms governing, AP subpopulations within human MSNA.

Parsing inter- and intra-individual variability in key nervous system mechanisms of stress responsivity and across functional domains

Exposure to stressful events is omnipresent in modern human life, yet people show considerable heterogeneity in the impact of stress exposure(s) on their functionality and overall health. Encounter with stressor(s) is counteracted by an intricate repertoire of nervous-system responses. This narrative review starts with a brief summary of the vast evidence that supports heart rate variability, cortisol secretion, and large-scale cortical network interactions as kay physiological, endocrinological, and neural mechanisms of stress responsivity, respectively. The second section highlights potential sources for inter-individual variability in these mechanisms, by focusing on biological, environmental, social, habitual, and psychological factors that may influence stress responsivity patterns and thus contribute to heterogeneity in the impact of stress exposure on functionality and health. The third section introduces intra-individually variability in stress responsivity across functional domains as a novel putative source for heterogeneity in the impact of stress exposure. Challenges and future directions are further discussed. Parsing inter- and intra-individual variability in nervous-system mechanisms of stress responsivity and across functional domains is critical towards potential clinical translation.

Acupuncture Relaxation, Vigilance Stage, and Autonomic Nervous System Function: A Comparative Study of Their Interrelationships

Objective: During acupuncture stimulation, autonomic nervous system (ANS) function changes toward being parasympathetic-dominant, with a transient decrease in heart rate (HR). The aim of this research was to determine the relationships between cortical relaxation and vigilance as observed on background electroencephalograms (EEGs), HR, and ANS function during deep acupuncture. Materials and Methods: This comparative study was conducted at Teikyo Heisei University, in Toshima-ku, Tokyo, Japan, with 27 healthy male volunteers. After resting for 20 minutes, the men received manual acupuncture at LI 10 on the left forearm for 2 minutes at a depth of 15-20 mm at a 1-Hz frequency while undergoing concurrent EEG and electrocardiography (ECG) monitoring. Each subject described his level of comfort during acupuncture. HR; power ratios (normalized units [n.u.]) of EEG alpha, beta, delta, and theta waves; and HR variability (HRV) indices were calculated. Results: In the subgroup who experienced discomfort, delta and theta n.u. were decreased while alpha n.u. were increased, indicating increased vigilance and decreased relaxation. In the subgroup who experienced comfort, there were no significant changes. HRV indices suggested parasympathetic-dominant changes in both subgroups. Weak correlations were observed between a decrease of theta n.u. and sympathetic-dominant changes in HRV indices. Conclusions: Alterations in background EEG activities were not the primary factors changing ANS function to parasympathetic-dominant and decreasing HR, but these alterations related to a weak secondary factor changing ANS function. EEG activity by which cortical relaxation and vigilance were represented was the weak secondary factor changing ANS function during acupuncture; the primary factor might be supraspinal reflection.

Peri-ictal hypoxia is related to extent of regional brain volume loss accompanying generalized tonic-clonic seizures

OBJECTIVES

Hypoxia, or abnormally low blood-oxygen levels, often accompanies seizures and may elicit brain structural changes in people with epilepsy which contribute to central processes underlying sudden unexpected death in epilepsy (SUDEP). The extent to which hypoxia may be related to brain structural alterations in this patient group remains unexplored.

METHODS

We analyzed high-resolution T1-weighted magnetic resonance imaging (MRI) to determine brain morphometric and volumetric alterations in people with generalized tonic-clonic seizures (GTCS) recorded during long-term video-electroencephalography (VEEG), recruited from two sites (n = 22), together with data from age- and sex-matched healthy controls (n = 43). Subjects were sub-divided into those with mild/moderate (GTCS-hypox-mild/moderate, n = 12) and severe (GTCS-hypox-severe, n = 10) hypoxia, measured by peripheral oxygen saturation (SpO2 ) during VEEG. Whole-brain voxel-based morphometry (VBM) and regional volumetry were used to assess group comparisons and correlations between brain structural measurements as well as the duration and extent of hypoxia during GTCS.

RESULTS

Morphometric and volumetric alterations appeared in association with peri-GTCS hypoxia, including volume loss in the periaqueductal gray (PAG), thalamus, hypothalamus, vermis, cerebellum, parabrachial pons, and medulla. Thalamic and PAG volume was significantly reduced in GTCS patients with severe hypoxia compared with GTCS patients with mild/moderate hypoxia. Brainstem volume loss appeared in both hypoxia groups, although it was more extensive in those with severe hypoxia. Significant negative partial correlations emerged between thalamic and hippocampal volume and extent of hypoxia, whereas vermis and accumbens volumes declined with increasing hypoxia duration.

SIGNIFICANCE

Brain structural alterations in patients with GTCS are related to the extent of hypoxia in brain sites that serve vital functions. Although the changes are associative only, they provide evidence of injury to regulatory brain sites related to respiratory manifestations of seizures.

Heart Rate Variability as an Index of Differential Brain Dynamics at Rest and After Acute Stress Induction

The brain continuously receives input from the internal and external environment. Using this information, the brain exerts its influence on both itself and the body to facilitate an appropriate response. The dynamic interplay between the brain and the heart and how external conditions modulate this relationship deserves attention. In high-stress situations, synchrony between various brain regions such as the prefrontal cortex and the heart may alter. This flexibility is believed to facilitate transitions between functional states related to cognitive, emotional, and especially autonomic activity. This study examined the dynamic temporal functional association of heart rate variability (HRV) with the interaction between three main canonical brain networks in 38 healthy male subjects at rest and directly after a psychosocial stress task. A sliding window approach was used to estimate the functional connectivity (FC) among the salience network (SN), central executive network (CEN), and default mode network (DMN) in 60-s windows on time series of blood-oxygen-level dependent (BOLD) signal. FC between brain networks was calculated by Pearson correlation. A multilevel linear mixed model was conducted to examine the window-by-window association between the root mean square of successive differences between normal heartbeats (RMSSD) and FC of network-pairs across sessions. Our findings showed that the minute-by-minute correlation between the FC and RMSSD was significantly stronger between DMN and CEN than for SN and CEN in the baseline session [b = 4.36, t(5025) = 3.20, p = 0.006]. Additionally, this differential relationship between network pairs and RMSSD disappeared after the stress task; FC between DMN and CEN showed a weaker correlation with RMSSD in comparison to baseline [b = −3.35, t(5025) = −3.47, p = 0.006]. These results suggest a dynamic functional interplay between HRV and the functional association between brain networks that varies depending on the needs created by changing conditions.

Heterogeneous baroreflex control of sympathetic action potential subpopulations in humans

KEY POINTS

Emission patterns in muscle sympathetic nerve activity stem from differently sized action potential (AP) subpopulations that express varying discharge probabilities. The mechanisms governing these firing behaviours are unclear. This study investigated the hypothesis that the arterial baroreflex exerts varying control over the different AP subpopulations. During baseline, medium APs expressed the greatest baroreflex slopes, while small and large APs exhibited weaker slopes. On going from baseline to lower body negative pressure (LBNP; simulated orthostatic stress), baroreflex slopes for some clusters of medium APs expressed the greatest increase, while slopes for large APs also increased but to a lesser degree. A subpopulation of previously silent larger APs was recruited with LBNP but these APs expressed weak baroreflex slopes. The arterial baroreflex heterogeneously regulates sympathetic AP subpopulations, exerting its strongest effect over medium APs. Weak baroreflex mechanisms govern the recruitment of latent larger AP subpopulations during orthostatic stress.

ABSTRACT

Muscle sympathetic nerve activity (MSNA) occurs primarily in bursts of action potentials (AP) with subpopulations that differ in size and discharge probabilities. The mechanisms determining these discharge patterns remain unclear. This study investigated the hypothesis that variations in AP discharge are due to subpopulation-specific baroreflex control. We employed multi-unit microneurography and a continuous wavelet analysis approach to extract sympathetic APs in 12 healthy individuals during baseline (BSL) and lower body negative pressure (LBNP; -40, -60, -80 mmHg). For each AP cluster, the baroreflex threshold slope was measured from the linear regression between AP probability (%) and diastolic blood pressure (mmHg). During BSL, the baroreflex exerted non-uniform regulation over AP subpopulations: medium-sized AP clusters expressed the greatest slopes while clusters of small and large APs expressed weaker slopes. On going from BSL to LBNP, the baroreflex slopes for each AP subpopulation were modified differently. Baroreflex slopes (%/mmHg) for some medium APs (cluster 5: -4.4 ± 4 to -9.1 ± 5) expressed the greatest increase with LBNP, while slopes for large APs (cluster 9: -1.3 ± 1 to -2.6 ± 2) also increased, but to a lesser degree. Slopes for small APs present at BSL exhibited reductions with LBNP (cluster 2: -3.9 ± 3 to -2.2 ± 3). Larger previously silent AP clusters recruited with LBNP expressed weak baroreflex regulation (cluster 14: -0.9 ± 1%/mmHg). The baroreflex exerts the strongest control over medium-sized APs. Augmenting baroreflex gain and upward resetting of discrete AP subpopulations active at BSL, as well as recruiting larger previously silent APs with weak baroreflex control, facilitates elevated MSNA during orthostatic stress.

Heart Rate Variability, Cue-Evoked Ventromedial Prefrontal Cortical Response, and Problem Alcohol Use in Adult Drinkers

BACKGROUND

Many studies employed cue exposure paradigms to investigate the neural processes underlying cue-elicited alcohol craving. Cue exposure elicits robust autonomic reactivity. However, whether or how cue-elicited autonomic response relates to the severity of alcohol misuse and the neural bases underlying the potential relationship remain unclear.

METHODS

We examined cue-related brain activations in association with heart rate variability, as indexed by the root mean square of the successive differences (RMSSD), during alcohol versus neutral cue blocks in 50 adult alcohol drinkers (24 men). Imaging and heart rate variability data were collected and processed with published routines. Mediation analyses were conducted to examine the interrelationship between regional activities, cue-elicited changes in RMSSD, and the severity of problem alcohol use, as assessed with the Alcohol Use Disorders Identification Test (AUDIT).

RESULTS

The results showed higher RMSSD during alcohol than during neutral cue exposures, with alcohol (vs. neutral) cue-evoked RMSSD positively correlated with AUDIT score. Further, alcohol (vs. neutral) cue-elicited activity in the ventromedial prefrontal cortex was negatively correlated both with increases in RMSSD and with the AUDIT score. Mediation analyses suggested that the RMSSD mediated the relationship between ventromedial prefrontal cortex cue activity and the AUDIT score.

CONCLUSIONS

These findings substantiate the neural correlates of the presumably parasympathetic response during alcohol cue exposure and the interrelationship among ventromedial prefrontal cortex activity, autonomic response, and problem alcohol use.

Effects of prefrontal transcranial direct current stimulation on autonomic and neuroendocrine responses to psychosocial stress in healthy humans

Prolonged or repeated activation of the stress response can have negative psychological and physical consequences. The prefrontal cortex (PFC) is thought to exert an inhibitory influence on the activity of autonomic and neuroendocrine stress response systems. In this study, we further investigated this hypothesis by increasing PFC excitability using transcranial direct current stimulation (tDCS). Healthy male participants were randomized to receive either anodal (excitatory) tDCS (n = 15) or sham stimulation (n = 15) over the left dorsolateral prefrontal cortex (DLPFC) immediately before and during the exposure to a psychosocial stress test. Autonomic (heart rate (HR) and its variability) and neuroendocrine (salivary cortisol) parameters were assessed. One single session of excitatory tDCS over the left DLPFC (i) reduced HR and favored a larger vagal prevalence prior to stress exposure, (ii) moderated stress-induced HR acceleration and sympathetic activation/vagal withdrawal, but (iii) had no effect on stress-induced cortisol release. However, anodal tDCS over the left DLPFC prevented stress-induced changes in the cortisol awakening response. Finally, participants receiving excitatory tDCS reported a reduction in their levels of state anxiety upon completion of the psychosocial stress test. In conclusion, this study provides first insights into the efficacy of one single session of excitatory tDCS over the left DLPFC in attenuating autonomic and neuroendocrine effects of psychosocial stress exposure. These findings might be indicative of the important role of the left DLPFC, which is a cortical target for noninvasive brain stimulation treatment of depression, for successful coping with stressful stimuli.

Host in the machine: A neurobiological perspective on psychological stress and cardiovascular disease

Psychological stress still attracts scientific, clinical, and public interest because of its suspected connection to health, particularly cardiovascular health. Psychological stress is thought to arise from appraisal processes that imbue events and contexts with personal significance and threat-related meaning. These appraisal processes are also thought to be instantiated in brain systems that generate and control peripheral physiological stress reactions through visceral motor (brain-to-body) and visceral sensory (body-to-brain) mechanisms. In the short term, physiological stress reactions may enable coping and adaptive action. Among some individuals, however, the patterning of these reactions may predict or contribute to pathology in multiple organ systems, including the cardiovascular system. At present, however, we lack a precise understanding of the brain systems and visceral control processes that link psychological appraisals to patterns of stress physiology and physical health. This understanding is important: A mechanistic account of how the brain connects stressful experiences to bodily changes and health could help refine biomarkers of risk and targets for cardiovascular disease prevention and intervention. We review research contributing to this understanding, focusing on the neurobiology of cardiovascular stress reactivity and cardiovascular health. We suggest that a dysregulation of visceral motor and visceral sensory processes during stressful experiences may confer risk for poor cardiovascular health among vulnerable individuals. We further describe a need for new interpretive frameworks and markers of this brain-body dysregulation in cardiovascular behavioral medicine. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Altered brain connectivity in sudden unexpected death in epilepsy (SUDEP) revealed using resting-state fMRI

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The functional architecture among regulatory structures, and the whole brain, is less modular in confirmed cases of SUDEP and those at high-risk.

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Altered functional organisation may mean potential impairment of communication among key regulatory circuits.

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SUDEP is associated with regional connectivity disruptions among cortical and sub-cortical regulatory sites.

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Medial thalamic connectivity was significantly altered in SUDEP compared with all control groups, including those at high-risk.

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Increases in the number, and a shift in organisation, of hubs appears to relate to lower mortality risk.

The circumstances surrounding SUDEP suggest autonomic or respiratory collapse, implying central failure of regulation or recovery. Characterisation of the communication among brain areas mediating such processes may shed light on mechanisms and noninvasively indicate risk.

We used rs-fMRI to examine network properties among brain structures in people with epilepsy who suffered SUDEP (n = 8) over an 8-year follow-up period, compared with matched high- and low-risk subjects (n = 16/group) who did not suffer SUDEP during that period, and a group of healthy controls (n = 16). Network analysis was employed to explore connectivity within a ‘regulatory-subnetwork’ of brain regions involved in autonomic and respiratory regulation, and over the whole-brain.

Modularity, the extent of network organization into separate modules, was significantly reduced in the regulatory-subnetwork, and the whole-brain, in SUDEP and high-risk. Increased participation, a local measure of inter-modular belonging, was evident in SUDEP and high-risk groups, particularly among thalamic structures. The medial prefrontal thalamus was increased in SUDEP compared with all other control groups, including high-risk. Patterns of hub topology were similar in SUDEP and high-risk, but were more extensive in low-risk patients, who displayed greater hub prevalence and a radical reorganization of hubs in the subnetwork.

SUDEP is associated with reduced functional organization among cortical and sub-cortical brain regions mediating autonomic and respiratory regulation. Living high-risk subjects demonstrated similar patterns, suggesting such network measures may provide prospective risk-indicating value, though a crucial difference between SUDEP and high-risk was altered connectivity of the medial thalamus in SUDEP, which was also elevated compared with all sub-groups. Disturbed thalamic connectivity may reflect a potential non-invasive marker of elevated SUDEP risk.

Role of Exosomes in Central Nervous System Diseases

There are many types of intercellular communication, and extracellular vesicles are one of the important forms of this. They are released by a variety of cell types, are heterogeneous, and can roughly be divided into microvesicles and exosomes according to their occurrence and function. Of course, exosomes do not just play a role in cell-to-cell communication. In the nervous system, exosomes can participate in intercellular communication, maintain the myelin sheath, and eliminate waste. Similarly, exosomes in the brain can play a role in central nervous system diseases, such as stroke, Alzheimer's disease (AD), Parkinson's disease (PD), prion disease, and traumatic encephalopathy (CTE), with both positive and negative effects (such as the transfer of misfolded proteins). Exosomes contain a variety of key bioactive substances and can therefore be considered as a snapshot of the intracellular environment. Studies have shown that exosomes from the central nervous system can be found in cerebrospinal fluid and peripheral body fluids, and that their contents will change with disease occurrence. Because exosomes can penetrate the blood brain barrier (BBB) and are highly stable in peripheral circulation, they can protect disease-related molecules well and therefore, using exosomes as a biomarker of central nervous system diseases is an attractive prospect as they can be used to monitor disease development and enable early diagnosis and treatment optimization. In this review, we discuss the current state of knowledge of exosomes, and introduce their pathophysiological roles in different diseases of the central nervous system as well as their roles and applications as a viable pathological biomarker.

Ventromedial prefrontal cortex connectivity during and after psychological stress in women

The ventromedial prefrontal cortex (vmPFC) integrates sensory, affective, memory-related, and social information from diverse brain systems to coordinate behavioral and peripheral physiological responses according to contextual demands that are appraised as stressful. However, the functionality of the vmPFC during stressful experiences is not fully understood. Among 40 female participants, the present study evaluated (a) functional connectivity of the vmPFC during exposure to and recovery following an acute psychological stressor, (b) associations among vmPFC functional connectivity, heart rate, and subjective reports of stress across individuals, and (c) whether patterns of vmPFC functional connectivity were associated with distributed brain networks. Results showed that psychological stress increased vmPFC functional connectivity with individual brain areas implicated in stressor processing (e.g., insula, amygdala, anterior cingulate cortex) and decreased connectivity with the posterior cingulate cortex and thalamus. There were no statistical differences in vmPFC connectivity to individual brain areas during recovery, as compared with baseline. Spatial similarity analyses revealed stressor-evoked increased connectivity of the vmPFC with the so-called dorsal attention, ventral attention, and frontoparietal networks, as well as decreased connectivity with the default mode network. During recovery, vmPFC connectivity increased with the frontoparietal network. Finally, individual differences in heart rate and perceived stress were associated with vmPFC connectivity to the ventral attention, frontoparietal, and default mode networks. Psychological stress appears to alter network-level functional connectivity of the vmPFC in a manner that further relates to individual differences in stressor-evoked cardiovascular and affective reactivity.

Reduced brainstem functional connectivity in patients with peripheral autonomic failure

Autonomic homeostasis is dependent upon several brainstem nuclei, as well as several cortical and subcortical structures. Together, these sites make up, in part, the central autonomic network. Neurogenic orthostatic hypotension (NOH) is a cardinal feature of autonomic failure that occurs due to a failure to increase sympathetic efferent activity in response to postural changes. Therefore, the purpose of the current study was to investigate brainstem functional connectivity in NOH patients with peripheral autonomic lesions resulting in autonomic failure. Fifteen controls (63 ± 13 years) and fifteen Neurogenic Orthostatic Hypotension patients (67 ± 6 years; p = .2) with peripheral autonomic dysfunction completed 5-min of rest and three Valsalva maneuvers during a functional brain scan. Functional connectivity from the brainstem to cortical and subcortical structures were contrasted between patients and controls. At rest controls had significantly greater brainstem connectivity to the anterior cingulate cortex (T-value: 4.29), left anterior insula (T-value:3.31), left putamen (T-value:3.31) and bilateral thalamus (T_RIGHT-value: 3.83; T_LEFT-value:4.25) (p-FDR < 0.005). During Valsalva, controls showed significantly more connectivity between the brainstem and both the left anterior (cerebellum 4/5) and bilateral posterior cerebellum (cerebellar 9 and left cerebellar 6). Other cerebellar regions included brainstem-to-vermis. Other brainstem-to-cortical and subcortical regions included: bilateral putamen, posterior cingulate cortex (PCC), amygdala and medial prefrontal cortex. There was a significant negative correlation between the brainstem-cerebellar connectivity and severity of autonomic dysfunction (p < .01). During recovery phase of the Valsalva, controls had greater brainstem connectivity to the left thalamus (T-value:4.17); PCC (T-value:3.32); right putamen (T-value:3.28); right paracingulate gyrus (T-value:3.25) and left posterior cerebellum (C9) (T-value:3.21) (p-FDR < 0.05). The effect sizes for each brainstem connectivity during Valsalva and recovery ranged from moderate to strong. Patients with autonomic failure show reduced coupling between the brainstem and regions of the central autonomic network, including the cerebellum, insula, thalamus and cingulate cortices. Connectivity was associated with autonomic impairment. These findings may suggest impaired brainstem connectivity in patients with autonomic failure.

A Focus on the Functions of Area 25

Subcallosal area 25 is one of the least understood regions of the anterior cingulate cortex, but activity in this area is emerging as a crucial correlate of mood and affective disorder symptomatology. The cortical and subcortical connectivity of area 25 suggests it may act as an interface between the bioregulatory and emotional states that are aberrant in disorders such as depression. However, evidence for such a role is limited because of uncertainty over the functional homologue of area 25 in rodents, which hinders cross-species translation. This emphasizes the need for causal manipulations in monkeys in which area 25, and the prefrontal and cingulate regions in which it is embedded, resemble those of humans more than rodents. In this review, we consider physiological and behavioral evidence from non-pathological and pathological studies in humans and from manipulations of area 25 in monkeys and its putative homologue, the infralimbic cortex (IL), in rodents. We highlight the similarities between area 25 function in monkeys and IL function in rodents with respect to the regulation of reward-driven responses, but also the apparent inconsistencies in the regulation of threat responses, not only between the rodent and monkey literatures, but also within the rodent literature. Overall, we provide evidence for a causal role of area 25 in both the enhanced negative affect and decreased positive affect that is characteristic of affective disorders, and the cardiovascular and endocrine perturbations that accompany these mood changes. We end with a brief consideration of how future studies should be tailored to best translate these findings into the clinic.

Blood Pressure in Seizures and Epilepsy

In this narrative review, we summarize the current knowledge of neurally mediated blood pressure (BP) control and discuss how recently described epilepsy- and seizure-related BP alterations may contribute to premature mortality and sudden unexpected death in epilepsy (SUDEP). Although people with epilepsy display disturbed interictal autonomic function with a shift toward predominant sympathetic activity, prevalence of arterial hypertension is similar in people with and without epilepsy. BP is transiently increased in association with most types of epileptic seizures but may also decrease in some, illustrating that seizure activity can cause both a decrease and increase of BP, probably because of stimulation or inhibition of distinct central autonomic function by epileptic activity that propagates into different neuronal networks of the central autonomic nervous system. The principal regulatory neural loop for short-term BP control is termed baroreflex, mainly involving peripheral sensors and brain stem nuclei. The baroreflex sensitivity (BRS, expressed as change of interbeat interval per change in BP) is intact after focal seizures, whereas BRS is markedly impaired in the early postictal period following generalized convulsive seizures (GCS), possibly due to metabolically mediated muscular hyperemia in skeletal muscles, a massive release of catecholamines and compromised brain stem function. Whilst most SUDEP cases are probably caused by a cardiorespiratory failure during the early postictal period following GCS, a profoundly disturbed BRS may allow a life-threatening drop of systemic BP in the aftermath of GCS, as recently reported in a patient as a plausible cause of SUDEP in a few patients.

Altered brain diffusion tensor imaging indices in adolescents with the Fontan palliation

PURPOSE

Single ventricle heart disease (SVHD) patients show injury in brain sites that regulate autonomic, mood, and cognitive functions. However, the nature (acute or chronic changes) and extent of brain injury in SVHD are unclear. Our aim was to examine regional brain tissue damage in SVHD over controls using DTI-based mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD), and fractional anisotropy (FA) procedures.

METHODS

We collected two DTI series (3.0-T MRI), mood and cognitive data, from 27 SVHD and 35 control adolescents. Whole-brain MD, AD, RD, and FA maps were calculated from each series, realigned and averaged, normalized to a common space, smoothed, and compared between groups using ANCOVA (covariates, age and sex; false discovery rate, p < 0.05). Region-of-interest analyses were performed to calculate MD, AD, RD, and FA values for magnitude assessment between groups.

RESULTS

SVHD patients showed impaired mood and cognitive functions over healthy adolescents. Multiple brain sites in SVHD showed increased MD values, including the insula, caudate, cingulate, hypothalamus, thalamus, medial prefrontal and frontal cortices, parahippocampal gyrus, hippocampus, precentral gyrus, amygdala, cerebellum, corpus callosum, basal forebrain, mammillary bodies, internal capsule, midbrain, fornix, and occipital, parietal, and temporal cortices, indicating chronic tissue changes. Similar areas showed either increased AD or RD values, with RD changes more enhanced over AD in SVHD compared to controls. Few brain regions emerged with increased or decreased FA values in SVHD patients over controls.

CONCLUSION

SVHD adolescents, more than a decade from their last surgical procedure, show widespread brain abnormalities in autonomic, mood, and cognitive regulatory areas. These findings indicate that brain injury is in a chronic stage in SVHD with predominantly myelin changes that may result from previous hypoxia/ischemia- or developmental-induced processes.

Surge of corticocardiac coupling in SHRSP rats exposed to forebrain cerebral ischemia

Sudden death is an important but underrecognized consequence of stroke. Acute stroke can disturb central control of autonomic function and result in cardiac dysfunction and sudden death. Previous study showed that bilateral common carotid artery ligation (BCCAL) in the spontaneously hypertensive stroke-prone rat strain (SHRSP) is a well-established model for forebrain ischemic sudden death. This study aims to investigate the temporal dynamic changes in electrical activities of the brain and heart and functional interactions between the two vital organs following forebrain ischemia. EEG and ECG signals were simultaneously collected from nine SHRSP and eight Wistar-Kyoto (WKY) rats. RR interval was analyzed to investigate the cardiac response to brain ischemia. EEG power and coherence (CCoh) analysis were conducted to study the cortical response. Corticocardiac coherence (CCCoh) and directional connectivity (CCCon) were analyzed to determine brain-heart connection. Heart rate variability (HRV) was analyzed to evaluate autonomic functionality. BCCAL resulted in 100% mortality in SHRSP within 14 h, whereas no mortality was observed in WKY rats. The functionality of both the brain and the heart were significantly altered in SHRSP compared with WKY rats after BCCAL. SHRSP, but not WKY rats, exhibited intermittent surge of CCCoh, which paralleled the elevated CCCon and reduced HRV, following the onset of ischemia until sudden death. Elevated brain-heart coupling invariably associated with the disruption of the autonomic nervous system and the risk of sudden death. This study may improve our understanding of the mechanism of forebrain ischemia-induced sudden death. NEW & NOTEWORTHY This study demonstrates a marked surge of corticocardiac coupling in rats dying from focal cerebral ischemia, consistent with our earlier data in rats exposed to fatal asphyxia. Since the bidirectional electrical signal coupling (corticocardiac coherence) and communication (corticocardiac connectivity) between the brain and the heart are only identified in dying animals, they could be used as potential biomarkers to predict the risk of sudden death.

[A role of the autonomic nervous system in cerebro-cardiac disorders]

The authors consider anatomical/physiological characteristics and a role of different autonomic CNS regions, including insula cortex, amygdala complex, anterior cingulate cortex, ventral medial prefrontal cortex, hypothalamus and epiphysis, involved in the regulation of cardiovascular activity. The damage of these structures, e.g., due to the acute disturbance of cerebral blood circulation, led to arrhythmia, including fatal arrhythmia, in previously intact myocardium; systolic and diastolic dysfunction, ischemic changes considered in the frames of cerebro-cardial syndrome. On the cellular level, the disturbance of autonomic regulation resulted in catechol amine excitotoxicity, oxidative stress and free radical myocardium injury.

Feedforward- and motor effort-dependent increase in prefrontal oxygenation during voluntary one-armed cranking

KEY POINTS

Some cortical areas are believed to transmit a descending signal in association with motor intention and/or effort that regulates the cardiovascular system during exercise (termed central command). However, there was no evidence for the specific cortical area responding prior to arbitrary motor execution and in proportion to the motor effort. Using a multichannel near-infrared spectroscopy system, we found that the oxygenation of the dorsolateral and ventrolateral prefrontal cortices on the right side increases in a feedforward- and motor effort-dependent manner during voluntary one-armed cranking with the right arm. This finding may suggest a role of the dorsolateral and ventrolateral prefrontal cortices in triggering off central command and may help us to understand impaired regulation of the cardiovascular system in association with lesion of the prefrontal cortex.

ABSTRACT

Output from higher brain centres (termed central command) regulates the cardiovascular system during exercise in a feedforward- and motor effort-dependent manner. This study aimed to determine a cortical area responding prior to arbitrarily started exercise and in proportion to the effort during exercise. The oxygenation responses in the frontal and frontoparietal areas during one-armed cranking with the right arm were measured using multichannel near-infrared spectroscopy, as indexes of regional blood flow responses, in 20 subjects. The intensity of voluntary exercise was 30% and 60% of the maximal voluntary effort (MVE). At the start period of both voluntary cranking tasks, the oxygenation increased (P < 0.05) only in the lateral and dorsal part of the dorsolateral prefrontal cortex (DLPFC), ventrolateral prefrontal cortex (VLPFC) and sensorimotor cortices. Then, the oxygenation increased gradually in all cortical areas during cranking at 60% MVE, while oxygenation increased only in the frontoparietal area and some of the frontal area during cranking at 30% MVE. The rating of perceived exertion to the cranking tasks correlated (P < 0.05) with the oxygenation responses on the right side of the lateral-DLPFC (r = 0.46) and VLPFC (r = 0.48) and the frontopolar areas (r = 0.47-0.49). Motor-driven passive one-armed cranking decreased the oxygenation in most cortical areas, except the contralateral frontoparietal areas. Accordingly, the lateral-DLPFC and VLPFC on the right side would respond in a feedforward- and motor effort-dependent manner during voluntary exercise with the right arm. Afferent inputs from mechanosensitive afferents may decrease the cortical oxygenation.

Cerebellar impairment during an orthostatic challenge in patients with neurogenic orthostatic hypotension

OBJECTIVE

Compare activation patterns within the cortical autonomic network in patients with neurogenic orthostatic hypotension (NOH) versus healthy age-matched controls during an orthostatic challenge.

METHODS

Fifteen health controls and 15 NOH patients performed 3 Valsalva maneuvers, and 5-min of lower-body negative pressure (LBNP) during a functional brain MRI.

RESULTS

Compared to controls, NOH patients had significantly less activation within the cerebellum during both LBNP and VM. Both groups had significant activation of the bilateral insula and left thalamus during LBNP. No significant differences were found during the recovery phase of LBNP.

CONCLUSIONS

The cerebellum, which plays an important role in vestibulo-sympathetic reflexes, important for blood pressure adjustments during postural changes, appear to be affected in patients with NOH. The cerebellum also appears to be affected during other baroreflex mediated stressors such as the VM.

SIGNIFICANCE

Orthostatic reflexes mediated by the cerebellum may be impaired in patients with NOH. The results suggest an additional pathological pathway in patients with autonomic failure.

The role of the paravertebral ganglia in human sympathetic neural discharge patterns

KEY POINTS

The mechanisms affecting recruitment patterns of postganglionic sympathetic nerves remain unclear. The divergent and convergent preganglionic innervation patterns of postganglionic neurons and the presence of differently sized postganglionic nerves suggest that the ganglia may participate in modifying the discharge patterns of single sympathetic postganglionic neurons innervating the skeletal muscle circulation. Whether the ganglia affect the ordered behaviour of varying sized postganglionic sympathetic neurons in humans has not been studied. Trimethaphan infusion produced an ordered pattern of action potential (AP) de-recruitment whereby the firing of larger, low probability APs present at baseline was abolished first, followed by progressive decreased probability of smaller APs. Although integrated sympathetic bursts were no longer detected after several minutes of trimethaphan, firing of the smallest APs was detected. These data suggest the ganglia affect the distribution of firing probabilities exhibited by differently sized sympathetic neurons. The ganglia may contribute to sympathetic neural emission patterns involved in homeostatic regulation.

ABSTRACT

Do the ganglia contribute to the ordered behaviour of postganglionic neuronal discharge within the sympathetic nervous system? To further understand the functional organization of the sympathetic nervous system we employed the microneurographic approach to record muscle sympathetic nerve activity (MSNA) and a continuous wavelet transform to study postganglionic action potential (AP) behaviour during nicotinic blockade at the ganglia (trimethaphan camsylate, 1-7 mg min-1 ) in seven females (37 ± 5 years). Trimethaphan elicited a progressive reduction in sympathetic outflow characterized by fewer integrated bursts with decaying amplitude. Underlying trimethaphan-mediated attenuations in integrated MSNA were reductions in AP incidence (186 ± 101 to 29 ± 31 AP (100 beats)-1 ) and AP content per integrated burst (7 ± 2 to 3 ± 1 APs burst-1 ) (both P < 0.01) in the final minute of detectable bursting activity in the trimethaphan condition, compared to baseline. We observed an ordered de-recruitment of larger to smaller AP clusters active at baseline (14 ± 3 to 8 ± 2 active AP clusters, P < 0.01). Following cessation of integrated bursts in the trimethaphan condition, the smallest 6 ± 2 sympathetic AP clusters persisted to fire in an asynchronous pattern (49 ± 41 AP (100 beats)-1 ) in all participants. Valsalva's manoeuvre did not increase the incidence of these persistent APs (60 ± 42 AP (100 beats)-1 , P = 0.52), or recruit any larger APs in six of seven participants (6 ± 1 total AP clusters, P = 0.30). These data suggest that the ganglia participate in the ordered recruitment of differently sized postganglionic sympathetic nerves.

The human cortical autonomic network and volitional exercise in health and disease

The autonomic nervous system elicits continuous beat-by-beat homeostatic adjustments to cardiovascular control. These modifications are mediated by sensory inputs (e.g., baroreceptors, metaboreceptors, pulmonary, thermoreceptors, and chemoreceptors afferents), integration at the brainstem control centres (i.e., medulla), and efferent autonomic neural outputs (e.g., spinal, preganglionic, and postganglionic pathways). However, extensive electrical stimulation and functional imaging research show that the brain's higher cortical regions (e.g., insular cortex, medial prefrontal cortex, anterior cingulate cortex) partake in homeostatic regulation of the cardiovascular system at rest and during exercise. We now appreciate that these cortical areas form a network, namely the "cortical autonomic network" (CAN), which operate as part of a larger central autonomic network comprising 2-way communication of cortical and subcortical areas to exert autonomic influence. Interestingly, differential patterns of CAN activity and ensuing cardiovascular control are present in disease states, thereby highlighting the importance of considering the role of CAN as an integral aspect of cardiovascular regulation in health and disease. This review discusses current knowledge on human cortical autonomic activation during volitional exercise, and the role of exercise training on this activation in both health and disease.