Forebrain regions associated with postexercise differences in autonomic and cardiovascular function during baroreceptor unloading

Central α2-adrenergic mechanisms regulate human sympathetic neuronal discharge strategies

The present study investigated the impact of central α2-adrenergic mechanisms on sympathetic action potential (AP) discharge, recruitment and latency strategies. We used the microneurographic technique to record muscle sympathetic nerve activity and a continuous wavelet transform to investigate postganglionic sympathetic AP firing during a baseline condition and an infusion of a α2-adrenergic receptor agonist, dexmedetomidine (10 min loading infusion of 0.225 µg kg-1; maintenance infusion of 0.1-0.5 µg kg h-1) in eight healthy individuals (28 ± 7 years, five females). Dexmedetomidine reduced mean pressure (92 ± 7 to 80 ± 8 mmHg, P < 0.001) but did not alter heart rate (61 ± 13 to 60 ± 14 bpm; P = 0.748). Dexmedetomidine reduced sympathetic AP discharge (126 ± 73 to 27 ± 24 AP 100 beats-1, P = 0.003) most strongly for medium-sized APs (normalized cluster 2: 21 ± 10 to 5 ± 5 AP 100 beats-1; P < 0.001). Dexmedetomidine progressively de-recruited sympathetic APs beginning with the largest AP clusters (12 ± 3 to 7 ± 2 clusters, P = 0.002). Despite de-recruiting large AP clusters with shorter latencies, dexmedetomidine reduced AP latency across remaining clusters (1.18 ± 0.12 to 1.13 ± 0.13 s, P = 0.002). A subset of six participants performed a Valsalva manoeuvre (20 s, 40 mmHg) during baseline and the dexmedetomidine infusion. Compared to baseline, AP discharge (Δ 361 ± 292 to Δ 113 ± 155 AP 100 beats-1, P = 0.011) and AP cluster recruitment elicited by the Valsalva manoeuvre were lower during dexmedetomidine (Δ 2 ± 1 to Δ 0 ± 2 AP clusters, P = 0.041). The reduction in sympathetic AP latency elicited by the Valsalva manoeuvre was not affected by dexmedetomidine (Δ -0.09 ± 0.07 to Δ -0.07 ± 0.14 s, P = 0.606). Dexmedetomidine reduced baroreflex gain, most strongly for medium-sized APs (normalized cluster 2: -6.0 ± 5 to -1.6 ± 2 % mmHg-1; P = 0.008). These data suggest that α2-adrenergic mechanisms within the central nervous system modulate sympathetic postganglionic neuronal discharge, recruitment and latency strategies in humans. KEY POINTS: Sympathetic postganglionic neuronal subpopulations innervating the human circulation exhibit complex patterns of discharge, recruitment and latency. However, the central neural mechanisms governing sympathetic postganglionic discharge remain unclear. This microneurographic study investigated the impact of a dexmedetomidine infusion (α2-adrenergic receptor agonist) on muscle sympathetic postganglionic action potential (AP) discharge, recruitment and latency patterns. Dexmedetomidine infusion inhibited the recruitment of large and fast conducting sympathetic APs and attenuated the discharge of medium sized sympathetic APs that fired during resting conditions and the Valsalva manoeuvre. Dexmedetomidine infusion elicited shorter sympathetic AP latencies during resting conditions but did not affect the reductions in latency that occurred during the Valsalva manoeuvre. These data suggest that α2-adrenergic mechanisms within the central nervous system modulate sympathetic postganglionic neuronal discharge, recruitment and latency strategies in humans.

Objective sleep measures in chronic fatigue syndrome patients: A systematic review and meta-analysis

Patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) often report disrupted and unrefreshing sleep in association with worsened fatigue symptoms. However, the nature and magnitude of sleep architecture alteration in ME/CFS is not known, with studies using objective sleep measures in ME/CFS generating contradictory results. The current manuscript aimed to review and meta-analyse of case-control studies with objective sleep measures in ME/CSF. A search was conducted in PubMed, Scopus, Medline, Google Scholar, and Psychoinfo databases. After review, 24 studies were included in the meta-analysis, including 20 studies with 801 adults (ME/CFS = 426; controls = 375), and 4 studies with 477 adolescents (ME/CFS = 242; controls = 235), who underwent objective measurement of sleep. Adult ME/CFS patients spend longer time in bed, longer sleep onset latency, longer awake time after sleep onset, reduced sleep efficiency, decreased stage 2 sleep, more Stage 3, and longer rapid eye movement sleep latency. However, adolescent ME/CFS patients had longer time in bed, longer total sleep time, longer sleep onset latency, and reduced sleep efficiency. The meta-analysis results demonstrate that sleep is altered in ME/CFS, with changes seeming to differ between adolescent and adults, and suggesting sympathetic and parasympathetic nervous system alterations in ME/CFS.

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.

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.

Lower Body Negative Pressure: Physiological Effects, Applications, and Implementation

This review presents lower body negative pressure (LBNP) as a unique tool to investigate the physiology of integrated systemic compensatory responses to altered hemodynamic patterns during conditions of central hypovolemia in humans. An early review published in Physiological Reviews over 40 yr ago (Wolthuis et al. Physiol Rev 54: 566-595, 1974) focused on the use of LBNP as a tool to study effects of central hypovolemia, while more than a decade ago a review appeared that focused on LBNP as a model of hemorrhagic shock (Cooke et al. J Appl Physiol (1985) 96: 1249-1261, 2004). Since then there has been a great deal of new research that has applied LBNP to investigate complex physiological responses to a variety of challenges including orthostasis, hemorrhage, and other important stressors seen in humans such as microgravity encountered during spaceflight. The LBNP stimulus has provided novel insights into the physiology underlying areas such as intolerance to reduced central blood volume, sex differences concerning blood pressure regulation, autonomic dysfunctions, adaptations to exercise training, and effects of space flight. Furthermore, approaching cardiovascular assessment using prediction models for orthostatic capacity in healthy populations, derived from LBNP tolerance protocols, has provided important insights into the mechanisms of orthostatic hypotension and central hypovolemia, especially in some patient populations as well as in healthy subjects. This review also presents a concise discussion of mathematical modeling regarding compensatory responses induced by LBNP. Given the diverse applications of LBNP, it is to be expected that new and innovative applications of LBNP will be developed to explore the complex physiological mechanisms that underline health and disease.

Functional neuroimaging of the central autonomic network: recent developments and clinical implications

Purpose

The central autonomic network (CAN) is an intricate system of brainstem, subcortical, and cortical structures that play key roles in the function of the autonomic nervous system. Prior to the advent of functional neuroimaging, in vivo studies of the human CAN were limited. The purpose of this review is to highlight the contribution of functional neuroimaging, specifically functional magnetic resonance imaging (fMRI), to the study of the CAN, and to discuss recent advances in this area. Additionally, we aim to emphasize exciting areas for future research.

Methods

We reviewed the existing literature in functional neuroimaging of the CAN. Here, we focus on fMRI research conducted in healthy human subjects, as well as research that has been done in disease states, to understand CAN function. To minimize confounding, papers examining CAN function in the context of cognition, emotion, pain, and affective disorders were excluded.

Results

fMRI has led to significant advances in the understanding of human CAN function. The CAN is composed of widespread brainstem and forebrain structures that are intricately connected and play key roles in reflexive and modulatory control of autonomic function.

Conclusions

fMRI technology has contributed extensively to current knowledge of CAN function. It holds promise to serve as a biomarker in disease states. With ongoing advancements in fMRI technology, there is great opportunity and need for future research involving the CAN.

[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.

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.

Motor, cognitive, and affective areas of the cerebral cortex influence the adrenal medulla

Modern medicine has generally viewed the concept of "psychosomatic" disease with suspicion. This view arose partly because no neural networks were known for the mind, conceptually associated with the cerebral cortex, to influence autonomic and endocrine systems that control internal organs. Here, we used transneuronal transport of rabies virus to identify the areas of the primate cerebral cortex that communicate through multisynaptic connections with a major sympathetic effector, the adrenal medulla. We demonstrate that two broad networks in the cerebral cortex have access to the adrenal medulla. The larger network includes all of the cortical motor areas in the frontal lobe and portions of somatosensory cortex. A major component of this network originates from the supplementary motor area and the cingulate motor areas on the medial wall of the hemisphere. These cortical areas are involved in all aspects of skeletomotor control from response selection to motor preparation and movement execution. The second, smaller network originates in regions of medial prefrontal cortex, including a major contribution from pregenual and subgenual regions of anterior cingulate cortex. These cortical areas are involved in higher-order aspects of cognition and affect. These results indicate that specific multisynaptic circuits exist to link movement, cognition, and affect to the function of the adrenal medulla. This circuitry may mediate the effects of internal states like chronic stress and depression on organ function and, thus, provide a concrete neural substrate for some psychosomatic illness.

Association between resting-state brain functional connectivity and muscle sympathetic burst incidence

The insula (IC) and cingulate are key components of the central autonomic network and central nodes of the salience network (SN), a set of spatially distinct but temporally correlated brain regions identified with resting-state (task free) functional MRI (rsMRI). To examine the SN's involvement in sympathetic outflow, we tested the hypothesis that individual differences in intrinsic connectivity of the SN correlate positively with resting postganglionic muscle sympathetic nerve activity (MSNA) burst incidence (BI) in subjects without and with obstructive sleep apnea (OSA). Overnight polysomnography, 5-min rsMRI, and fibular MSNA recording were performed in 36 subjects (mean age 57 yr; 10 women, 26 men). Independent component analysis (ICA) of the entire cohort identified the SN as including bilateral IC, pregenual anterior cingulate cortex (pgACC), midcingulate cortex (MCC), and the temporoparietal junction (TPJ). There was a positive correlation between BI and the apnea-hypopnea index (AHI) (P < 0.001), but dual-regression analysis identified no differences in SN functional connectivity between subjects with no or mild OSA (n = 17) and moderate or severe (n = 19) OSA. Correlation analysis relating BI to the strength of connectivity within the SN revealed large (i.e., spatial extent) and strong correlations for the left IC (P < 0.001), right pgACC/MCC (P < 0.006), left TPJ (P < 0.004), thalamus (P < 0.035), and cerebellum (P < 0.013). Indexes of sleep apnea were unrelated to BI and the strength of SN connectivity. There were no relationships between BI and default or sensorimotor network connectivity. This study links connectivity within the SN to MSNA, demonstrating several of its nodes to be key sympathoexcitatory regions.

Forebrain neurocircuitry associated with human reflex cardiovascular control

Physiological homeostasis depends upon adequate integration and responsiveness of sensory information with the autonomic nervous system to affect rapid and effective adjustments in end organ control. Dysregulation of the autonomic nervous system leads to cardiovascular disability with consequences as severe as sudden death. The neural pathways involved in reflexive autonomic control are dependent upon brainstem nuclei but these receive modulatory inputs from higher centers in the midbrain and cortex. Neuroimaging technologies have allowed closer study of the cortical circuitry related to autonomic cardiovascular adjustments to many stressors in awake humans and have exposed many forebrain sites that associate strongly with cardiovascular arousal during stress including the medial prefrontal cortex, insula cortex, anterior cingulate, amygdala and hippocampus. Using a comparative approach, this review will consider the cortical autonomic circuitry in rodents and primates with a major emphasis on more recent neuroimaging studies in awake humans. A challenge with neuroimaging studies is their interpretation in view of multiple sensory, perceptual, emotive and/or reflexive components of autonomic responses. This review will focus on those responses related to non-volitional baroreflex control of blood pressure and also on the coordinated responses to non-fatiguing, non-painful volitional exercise with particular emphasis on the medial prefrontal cortex and the insula cortex.

Correlation between baseline blood pressure and the brainstem FMRI response to isometric forearm contraction in human volunteers: a pilot study

It has been shown previously that changes in brainstem neural activity correlate with changes in both mean arterial pressure (MAP) and muscle sympathetic nerve activity (MSNA) during static handgrip (SHG). However, the relationship between baseline MAP and brainstem neural activity is unclear. We investigated changes in blood oxygen level-dependent (BOLD) signal induced by SHG in 12 young adults using BOLD functional magnetic resonance imaging (FMRI). An estimation of the blood pressure response to SHG was obtained in seven subjects during a session outside the MRI scanner and was used to model the blood pressure response to SHG inside the scanner. SHG at 40% of maximum grip increased MAP (mean ± s.d.) at the end of the 180-s squeeze from 85 ± 6 mm Hg to 108 ± 15 mm Hg, P = 0.0001. The brainstem BOLD signal change associated with SHG was localised to the ventrolateral medulla. This regional BOLD signal change negatively correlated with baseline MAP, r = -0.61, P = 0.01. This relationship between baseline MAP and brainstem FMRI responses to forearm contraction is suggestive of a possible role for brainstem activity in the control of MAP and may provide mechanistic insights into neurogenic hypertension.

Apnea-induced cortical BOLD-fMRI and peripheral sympathoneural firing response patterns of awake healthy humans

End-expiratory breath-holds (BH) and Mueller manoeuvres (MM) elicit large increases in muscle sympathetic nerve activity (MSNA). In 16 healthy humans (9♀, 35±4 years) we used functional magnetic resonance imaging with blood oxygen level-dependent (BOLD) contrast to determine the cortical network associated with such sympathoexcitation. We hypothesized that increases in MSNA evoked by these simulated apneas are accompanied by BOLD contrast changes in the insular cortex, thalamus and limbic cortex. A series of 150 whole-brain images were collected during 3 randomly performed 16-second end-expiratory BHs and MMs (-30 mmHg). The identical protocol was repeated separately with MSNA recorded from the fibular nerve. The time course of the sympathoexcitatory response to both breathing tasks were correlated with whole-brain BOLD signal changes. Brain sites demonstrating both positive (activation) and negative (deactivation) correlations with the MSNA time course were identified. Sympathetic burst incidence increased (p<0.001) from 29±6 (rest) to 49±6 (BH) and 47±6 bursts/100 heartbeats (MM). Increased neural activity (Z-scores) was identified in the right posterior and anterior insular cortices (3.74, 3.64), dorsal anterior cingulate (3.42), fastigial and dentate cerebellar nuclei (3.02, 3.34). Signal intensity decreased in the left posterior insula (3.28) and ventral anterior cingulate (3.01). Apnea both activates and inhibits elements of a cortical network involved in the generation of sympathetic outflow. These findings identify a neuroanatomical substrate to guide future investigations into central mechanisms contributing to disorders characterized by elevated basal MSNA and exaggerated sympathetic responses to simulated apneas such as sleep apnea and heart failure.

Cortical circuitry associated with reflex cardiovascular control in humans: does the cortical autonomic network "speak" or "listen" during cardiovascular arousal

Beginning with clinical evidence of fatal cardiac arrhythmias in response to severe stress, in epileptic patients, and following stroke, the role of the cerebral cortex in autonomic control of the cardiovascular system has gained both academic and clinical interest. Studies in anesthetized rodents have exposed the role of several forebrain regions involved in cardiovascular control. The introduction of functional neuroimaging techniques has enabled investigations into the conscious human brain to illuminate the temporal and spatial activation patterns of cortical regions that are involved with cardiovascular control through the autonomic nervous system. This symposia report emphasizes the research performed by the authors to understand the functional organization of the human forebrain in cardiovascular control during physical stressors of baroreceptor unloading and handgrip exercise. The studies have exposed important associations between activation patterns of the insula cortex, dorsal anterior cingulate, and the medial prefrontal cortex and cardiovascular adjustments to physical stressors. Furthermore, these studies provide functional anatomic evidence that sensory signals arising from baroreceptors and skeletal muscle are represented within the insula cortex and the medial prefrontal cortex, in addition to the sensory cortex. Thus, the cortical pathways subserving reflex cardiovascular control integrate viscerosensory inputs with outgoing traffic that modulates the autonomic nervous system.

Decreased cortical thickness in central hypoventilation syndrome

Central hypoventilation syndrome (CHS) is a rare condition characterized by hypoventilation during sleep, reduced ventilatory responsiveness to CO(2) and O(2), impaired perception of air hunger, and autonomic abnormalities. Neural impairments accompany the condition, including structural injury, impaired cerebral autoregulation, and dysfunctional autonomic control. The hypoventilation may induce cortical hypoxic injury, additional to consequences of maldevelopment from PHOX2B mutations present in most CHS subjects. We assessed cortical injury in clinically diagnosed CHS using high-resolution magnetic resonance imaging scans, collected from 14 CHS (mean age ± standard deviation [SD] 17.7 ± 5.0 years; 6 female) and 29 control (mean age ± SD, 17.9 ± 4.3 years; 12 female) subjects. We measured group differences in mean cortical thickness and age-thickness correlations using FreeSurfer software, accounting for age and sex (0.1 false discovery rate). Reduced thickness in CHS appeared in the dorsomedial frontal cortex and anterior cingulate; medial prefrontal, parietal, and posterior cingulate cortices; the insular cortex; anterior and lateral temporal lobes; and mid- and accessory motor strips. Normal age-related cortical thinning in multiple regions did not appear in CHS. The cortical thinning may contribute to CHS cardiovascular and memory deficits and may impair affect and perception of breathlessness. Extensive axonal injury in CHS is paralleled by reduced cortical tissue and absence of normal developmental patterns.

Structural modifications of the brain in acclimatization to high-altitude

Adaptive changes in respiratory and cardiovascular responses at high altitude (HA) have been well clarified. However, the central mechanisms underlying HA acclimatization remain unclear. Using voxel-based morphometry (VBM) and diffusion tensor imaging (DTI) with fractional anisotropy (FA) calculation, we investigated 28 Han immigrant residents (17–22 yr) born and raised at HA of 2616–4200 m in Qinghai-Tibetan Plateau for at least 17 years and who currently attended college at sea-level (SL). Their family migrated from SL to HA 2–3 generations ago and has resided at HA ever since. Control subjects were matched SL residents. HA residents (vs. SL) showed decreased grey matter volume in the bilateral anterior insula, right anterior cingulate cortex, bilateral prefrontal cortex, left precentral cortex, and right lingual cortex. HA residents (vs. SL) had significantly higher FA mainly in the bilateral anterior limb of internal capsule, bilateral superior and inferior longitudinal fasciculus, corpus callosum, bilateral superior corona radiata, bilateral anterior external capsule, right posterior cingulum, and right corticospinal tract. Higher FA values in those regions were associated with decreased or unchanged radial diffusivity coinciding with no change of longitudinal diffusivity in HA vs. SL group. Conversely, HA residents had lower FA in the left optic radiation and left superior longitudinal fasciculus. Our data demonstrates that HA acclimatization is associated with brain structural modifications, including the loss of regional cortical grey matter accompanied by changes in the white matter, which may underlie the physiological adaptation of residents at HA.

Reduced heart rate variability predicts poor sleep quality in a case-control study of chronic fatigue syndrome

Parasympathetic function is important in the induction and maintenance of sleep. We examined whether nocturnal vagal modulation of heart rate is related to the poor sleep quality commonly reported in chronic fatigue syndrome (CFS). Heart rate (HR, as R-R intervals) was continuously monitored during sleep in 20 patients with CFS and 20 matched control subjects. Questionnaires assessed demographic information, symptoms, functional impairment, and subjective sleep quality. CFS was associated with more sleep problems in general and poorer subjective sleep quality on the study night (all p < 0.003), and reports of repeated awakening during the night were 7 times more likely compared to healthy subjects (p = 0.017). Time and frequency-domain parameters of HR variability during sleep were significantly lower in patients with CFS (all p < 0.006). Multiple regression analyses revealed that heart rate variability (HRV) parameters were the best predictors of subjective sleep measures. This study identified significant reductions in vagal modulation of heart rate during sleep in CFS. Low HRV strongly predicted sleep quality-suggesting a pervasive state of nocturnal sympathetic hypervigilance in CFS.

The relation of ventromedial prefrontal cortex activity and heart rate fluctuations at rest

Recent studies applying functional magnetic resonance imaging have focused on the description of cerebral substrates of changes in cardiac function during diverse autonomic maneuvers or stressful cognitive tasks. These studies might be limited by the indistinguishable neuronal activity due to cognitive processes, which are known to influence autonomic function, and the 'baseline' activity in the central autonomic network. We therefore investigated 26 healthy volunteers in the magnetic resonance scanner to simultaneously obtain functional brain images and RR intervals (intervals between ventricular depolarizations) of the high-resolution electrocardiogram. The mean RR interval length within each functional scan was computed, which was finally convolved with the canonical hemodynamic response function to obtain a regressor for the functional time series. The resulting individual contrast image indicated a positive covariation of the blood oxygen level-dependent signal and RR interval length in the ventromedial prefrontal cortex (vmPFC). Furthermore, a reduced mean cross-approximate entropy value was shown for the interaction between the vmPFC and individual RR intervals. This suggests reduced asynchrony between the heart rate and vmPFC activity in contrast to other brain areas. Our findings confirm data obtained in animals describing the vmPFC as an important forebrain structure of the central autonomic network and an influence of the vmPFC in the cortical generation of efferent vagal activity. This finding needs to be investigated in diseases with known suppression of efferent vagal modulation.

Are decreases in insular regional cerebral blood flow sustained during postexercise hypotension?

Regional cerebral blood flow (rCBF) in the insular cortex (IC), a well-recognized site for central blood pressure (BP) modulation, is decreased at minute 10 during postexercise hypotension (PEH).

PURPOSE

To determine whether exercise-induced decreases in IC rCBF are associated with BP changes throughout PEH.

METHODS

Ten subjects were studied on three different days using a counterbalanced design with a randomized order for conditions; all were tested during a resting baseline and then at two of three time points postexercise: 10, 30, and 60 min. Data were collected for HR, mean BP, and rCBF using single-photon emission computed tomography as an index of brain activation.

RESULTS

Using ANOVA across conditions, there were differences (P < 0.05; mean +/- SD) for HR from baseline at minute 10 (+15 +/- 4 bpm) and minute 30 (+6 +/- 3 bpm) and for mean BP at minute 10 (-11 +/- 4 mm Hg) and minute 30 (-5 +/- 3 mm Hg). There were significant decreases (P < 0.05) in rCBF at both minutes 10 and 30 after exercise in the inferior thalamus and the right inferior IC regions. Although there were no decreases in BP or IC activity at minute 60, changes in right inferior posterior IC activity and BP were strongly correlated (r2 = 0.74; P < 0.05) postexercise.

CONCLUSIONS

Findings show that exercise-induced decreases in IC and thalamic activity may be a significant neural factor contributing to at least the first 30 min of PEH.

The usefulness of psychophysiology in the maintenance of cognitive life

In connection with the 14th World Congress of Psychophysiology--the Olympics of the Brain--IOP2008, held in my native Sankt-Petersburg, I am happy to state that the conceptualization of Psychophysiology as forming the objective scientific bases upon which the investigation and understanding of human cognitive and emotional processes became possible, was born in this country in 1886, under the wise leadership and personal initiatives of my Grandfather, the great Vladimir Michailovich Bechterev, whose contribution in the Experimental and Clinical Psychophysiology and Human Brain Sciences have been invaluable. The purpose of my present essay is to share with you some of my views and thoughts about the importance of Psychophysiology for the maintenance of daily intellectual life from childhood to adulthood and through the aging process.

WISE-2005: effect of aerobic and resistive exercises on orthostatic tolerance during 60 days bed rest in women

Cardiovascular deconditioning after long duration spaceflight is especially challenging in women who have a lower orthostatic tolerance (OT) compared with men. We hypothesized that an exercise prescription, combining supine aerobic treadmill exercise in a lower body negative pressure (LBNP) chamber followed by 10 min of resting LBNP, three to four times a week, and flywheel resistive training every third day would maintain orthostatic tolerance (OT) in women during a 60-day head-down-tilt bed rest (HDBR). Sixteen women were assigned to two groups (exercise, control). Pre and post HDBR OT was assessed with a tilt/LBNP test until presyncope. OT time (mean +/- SE) decreased from 17.5 +/- 1.0 min to 9.1 +/- 1.5 min (-50 +/- 6%) in control group (P < 0.001) and from 19.3 +/- 1.3 min to 13.0 +/- 1.9 min (-35 +/- 7%) in exercise group (P < 0.001), with no significant difference in OT time between the two groups after HDBR (P = 0.13). Nevertheless, compared with controls post HDBR, exercisers had a lower heart rate during supine rest (mean +/- SE, 71 +/- 3 vs. 85 +/- 4, P < 0.01), a slower increase in heart rate and a slower decrease in stroke volume over the course of tilt/LBNP test (P < 0.05). Blood volume (mean +/- SE) decreased in controls (-9 +/- 2%, P < 0.01) but was maintained in exercisers (-4 +/- 3%, P = 0.17).Our results suggest that the combined exercise countermeasure did not significantly improve OT but protected blood volume and cardiovascular response to sub tolerance levels of orthostatic stress.