Forebrain control of breathing: Anatomy and potential functions

Neuromodulation of dyspnea - A literature review

Dyspnea is a complex sensation resulting from the interplay between neural, biochemical, and mechanical pathways. Because dyspnea is a perception created and interpreted by the central nervous system, it could theoretically be targeted by neuromodulation approaches. This technique is used in pain to modulate the function of neuronal circuits. However, a safe surgical and/or non-invasive modus operandi is not established for refractory dyspnea. Nevertheless, the following literature review will discuss different neuromodulation techniques that may treat refractory dyspnea, even though the understanding of its pathophysiology is limited. More precisely, the diaphragm and its phrenic control, the ventral respiratory complexes (such as Kolliker-Fuse complex and the pre-Bötzinger complex), the vagal nerve, the periaqueductal gray, the insula, the cingular cortex, and the thalamus appear to play an important role in the pathophysiology of breathlessness. Consequently, deep brain stimulation, trigeminal nerve, spinal and vagal nerve stimulations are potentially effective approaches to diminish dyspnea. The discovery of useful dyspnea-reducing neuromodulation techniques could replace or be added to actual treatments like pulmonary rehabilitation, facial ventilators, oxygen, and opioids could be replaced, consequently enhancing the quality of life of dyspneic individuals.

Global coordination of brain activity by the breathing cycle

Neuronal activities that synchronize with the breathing rhythm have been found in humans and a host of mammalian species, not only in brain areas closely related to respiratory control or olfactory coding but also in areas linked to emotional and higher cognitive functions. In parallel, evidence is mounting for modulations of perception and action by the breathing cycle. In this Review, we discuss the extent to which brain activity locks to breathing across areas, levels of organization and brain states, and the physiological origins of this global synchrony. We describe how waves of sensory activity evoked by nasal airflow spread through brain circuits, synchronizing neuronal populations to the breathing cycle and modulating faster oscillations, cell assembly formation and cross-area communication, thereby providing a mechanistic link from breathing to neural coding, emotion and cognition. We argue that, through evolution, the breathing rhythm has come to shape network functions across species.

Alexander's Disease: Potential Drug Targets and Future Directions

Alexander's disease is a rare neurodegenerative disorder primarily characterized by upregulation of the GFAP gene and the formation of Rosenthal fibers. Its prognosis is fatal, with limited treatment options currently available. The GFAP protein is a marker for mature astrocytes. It results in the upregulation of reactive astroglioses. Reactive astroglioses is a neuroprotective condition that, when functioning correctly, helps protect the brain from stress and injury and prevents further injury. However, unregulated reactive astroglioses is linked with many neurodegenerative diseases. Due to the relative rarity in the incidence of AxD, treatment options have not been as widely investigated. This review explores potential drug targets that may impact GFAP gene expression, such as STAT3, GDNF, NF-kB, LCN-2, and the LPS pathway. These drug targets have previously been or are currently being explored in other neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. The only treatment option currently in clinical trial phases involves methods to induce the knockout of the GFAP gene. Due to GFAP's neuroprotective role in brain injury and stress, it is important to explore alternative treatment options that downregulate GFAP as opposed to shutting it off entirely.

Advances and research priorities in the respiratory management of ALS: Historical perspectives and new technologies

Respiratory involvement has been identified as a cardinal feature of amyotrophic lateral sclerosis (ALS) since its earliest descriptions in the 19th century. Since these initial reports, considerable research has been undertaken to clarify the pathophysiology and progression rates associated with respiratory compromise and effective management strategies have been developed. Clinical trials routinely incorporate respiratory measures as study end points, non-invasive ventilation is now widely used in the home setting, cough-assist techniques are commonly used, advanced neurophysiology techniques and wearable technologies have been integrated into respiratory monitoring protocols, and palliative guidelines have been developed to effectively manage respiratory distress. Despite the widespread implementation of these interventions, epidemiology studies are inconsistent and some studies suggest that survival in ALS has not improved significantly with the introduction of these measures. The outcomes of diaphragmatic pacing trials have been disappointing, advanced neurophysiology techniques are not routinely utilised, spinal and brainstem imaging are not commonly undertaken and significant geographical differences exist in proceeding to tracheostomy. The worldwide COVID pandemic has given impetus for remote monitoring, connected devices, video-consultations, and timely vaccinations in ALS; lessons that are invaluable long after the pandemic. Respiratory monitoring and management in ALS is a swiftly evolving facet of ALS care with considerable quality of life benefits.

Heart Rate Variability Biofeedback Training Can Improve Menopausal Symptoms and Psychological Well-Being in Women with a Diagnosis of Primary Breast Cancer: A Longitudinal Randomized Controlled Trial

Breast cancer survivors experience numerous chronic symptoms linked to autonomic dysfunction including anxiety, stress, insomnia, menopausal symptoms, and cognitive impairment. Effective non-pharmacological solutions to address these are currently lacking.

METHODS

Our three-armed longitudinal randomized controlled trial assessed the effectiveness of a 4-week remote smartphone-based heart rate variability biofeedback intervention which involved daily paced breathing at 6 breaths p/min; active (12 breaths p/min) and waitlist controls were included. Heart rate variability and self-reported cancer-related symptoms were assessed at baseline, post-, and 6 months-post intervention. Participants were 60 UK-based women with primary breast cancer history (6 to 60 months post-active treatment).

RESULTS

The intervention group showed significant increases in low-frequency heart rate variability over time (F (4, 103.89) = 2.862, p = 0.027, d = 0.33), long-lasting improvement in sleep quality (F (4, 88.04) = 4.87, p = 0.001, d = 0.43) and cessations in night sweats (X2 (2, N = 59) = 6.44, p = 0.04, Cramer's V = 0.33), and reduced anxiety post-intervention compared to the active and waitlist controls (F (4, 82.51) = 2.99, p = 0.023, d = 0.44). Other findings indicated that the intervention and active control participants reported lasting improvements in cognitive function, fatigue, and stress-related symptoms (all ps < 0.05). The waitlist group reported no symptom changes across time.

CONCLUSION

Heart rate variability biofeedback is a feasible intervention for addressing diverse chronic symptoms commonly reported by breast cancer survivors.

Muscles and Central Neural Networks Involved in Breathing: State of the Art

Breathing is a systemic act, which involves not only the lungs, but the entire body system. To have a comprehensive clinical picture, it is necessary to have all the patient's data; from this assumption, we can affirm that it is necessary to know all the muscles involved in breathing to understand how to obtain a comprehensive approach for the care and treatment of the patient to improve respiratory capacity. The text reviews the efferent connections of the respiratory centers and cites all the muscles that are involved in the mechanism of breathing and that are controlled and managed by the respiratory centers, starting from the muscular description of the cranial area, the bucco-cervical area, the cervicothoracic area, and the thoracic area. Knowing the function of the respiratory accessory muscles allows us to obtain, in some clinical cases, valuable data that can prove predictive of the diagnostic path of the pathology. This is the first article in the literature, to the authors' knowledge, that attempts to list and include in a single text all the muscles directly or indirectly involved in breathing. The goal of this narrative review article is to remind clinicians and researchers involved in the study of different muscular respiratory responses that we need to analyze and work all the skeletal musculature involved in breathing to better understand what happens in the pathological or physiological phases during breathing. This step will allow us to better individualize the therapeutic and training approach for healthy subjects.

Sudden Unexpected Death in Epilepsy: Central Respiratory Chemoreception

Sudden unexpected death in epilepsy (SUDEP) is a critical concern for individuals suffering from epilepsy, with respiratory dysfunction playing a significant role in its pathology. Fatal seizures are often characterized by central apnea and hypercapnia (elevated CO2 levels), indicating a failure in ventilatory control. Research has shown that both human epilepsy patients and animal models exhibit a reduced hypercapnic ventilatory response in the interictal (non-seizure) period, suggesting an impaired ability to regulate breathing in response to high CO2 levels. This review examines the role of central chemoreceptors-specifically the retrotrapezoid nucleus, raphe nuclei, nucleus tractus solitarius, locus coeruleus, and hypothalamus in this pathology. These structures are critical for sensing CO2 and maintaining respiratory homeostasis. Emerging evidence also implicates neuropeptidergic pathways within these chemoreceptive regions in SUDEP. Neuropeptides like galanin, pituitary adenylate cyclase-activating peptide (PACAP), orexin, somatostatin, and bombesin-like peptides may modulate chemosensitivity and respiratory function, potentially exacerbating respiratory failure during seizures. Understanding the mechanisms linking central chemoreception, respiratory control, and neuropeptidergic signaling is essential to developing targeted interventions to reduce the risk of SUDEP in epilepsy patients.

Corticolimbic structures activation during preparation and execution of respiratory manoeuvres in voluntary olfactory sampling: An intracranial EEG study

Volitional respiratory manoeuvres such as sniffing and apnoea play a key role in the active olfactory exploration of the environment. Their impairment by neurodegenerative processes could thus impair olfactory abilities with the ensuing impact on quality of life. Functional brain imaging studies have identified brain networks engaged in sniffing and voluntary apnoea, comprising the primary motor and somatosensory cortices, the insula, the anterior cingulate cortex and the amygdala. The temporal organization and the oscillatory activities of these networks are not known. To elucidate these aspects, we recorded intracranial electroencephalograms in six patients during voluntary sniffs and short apnoeas (12 s). The preparation phase of both manoeuvres involved increased alpha and theta activity in the posterior insula, amygdala and temporal regions, with a specific preparatory activity in the parahippocampus for the short apnoeas and the hippocampus for sniff. Subsequently, it narrowed to the superior and median temporal areas, immediately after the manoeuvres. During short apnoeas, a particular dynamic was observed, consisting of a rapid decline in alpha and theta activity followed by a slow recovery and increase. Volitional respiratory manoeuvres involved in olfactory control involve corticolimbic structures in both a preparatory and executive manner. Further studies are needed to determine whether diseases altering deep brain structures can disrupt these mechanisms and if such disruption contributes to the corresponding olfactory deficits. KEY POINTS: Both sniff manoeuvres and short apnoeas are associated with oscillatory activity predominantly in low-frequency bands (alpha and theta). Preparation of sniff manoeuvres and short apnoeas involve activities in low-frequency bands in the posterior insula and temporal regions that extend to amygdala during the execution of both manoeuvres. During short apnoeas, activities in low-frequency bands initially decline before continuously increasing until the apnoeas end.

Electrical stimulation of the sciatic nerve restores inspiratory diaphragm function in mice after spinal cord injury

Introduction

Spinal cord injury in the high cervical cord can impair breathing due to disruption of pathways between brainstem respiratory centers and respiratory motor neurons in the spinal cord. Electrical stimulation of limb afferents can increase ventilation in healthy humans and animals, but it is not known if limb afferent stimulation can improve breathing following a cervical injury.

Methods

We stimulated the sciatic nerve while using electromyography to measure diaphragm function in anesthetized mice following a cervical (C2) hemisection spinal cord injury, as well as in uninjured controls. The amplitude and frequency of inspiratory bursts was analyzed over a range of stimulation thresholds.

Results

We show that electrical stimulation (at sufficient current thresholds) of either the left or right sciatic nerve could restore inspiratory activity to the previously paralyzed diaphragm ipsilateral to a C2 hemisection injury at either acute (1 day) or chronic (2 months) stages after injury. We also show that sciatic nerve stimulation can increase the frequency and amplitude of diaphragm inspiratory bursts in uninjured mice.

Discussion

Our findings indicate that therapies targeting limb afferents could potentially be used to improve breathing in patients with cervical spinal cord injury and provide an experimental model to further investigate the neural pathways by which limb afferents can increase respiratory muscle activity.

Assessment of ante mortem welfare indicators and the pathophysiology of captive-bolt trauma in equids at slaughter

There is limited research into horse slaughter, particularly ante mortem welfare, and the effectiveness of captive-bolt gun (CBG) stunning, despite this being a widely used method worldwide. To address this evidence gap and explore associations between ante and post mortem factors, the welfare of 62 horses was assessed at a commercial Italian abattoir. Animal-based measures were used to identify stress-related behaviours and stunning effectiveness. A sub-sample (44%; 27/62) of heads were assessed for gross brain pathology. All animals in the study showed stress-related behaviours at all stages of the slaughter process. Additionally, 53% (33/62) of horses slipped in the stunning box, with poor floor surface condition and use of force associated with this. At least one sign of an ineffective stun was observed in 22% (14/62) of animals. Six animals were shot twice, with the application of a second shot significantly associated with a higher stress behaviour index score in the stunning box. Damage to critical brainstem structures was found in 85% (23/27) of heads that were assessed with gross pathology. An absence of damage to critical brainstem structures meant that animals were ten times more likely to show signs of ineffective stunning. These results highlight the risks to equine welfare throughout the slaughter process and suggest that mitigating ante mortem stress could improve stunning effectiveness, whilst CBG usage should be refined to ensure that critical brainstem structures are targeted.

Physiological Entrainment: A Key Mind-Body Mechanism for Cognitive, Motor and Affective Functioning, and Well-Being

BACKGROUND

The human sensorimotor system can naturally synchronize with environmental rhythms, such as light pulses or sound beats. Several studies showed that different styles and tempos of music, or other rhythmic stimuli, have an impact on physiological rhythms, including electrocortical brain activity, heart rate, and motor coordination. Such synchronization, also known as the "entrainment effect", has been identified as a crucial mechanism impacting cognitive, motor, and affective functioning.

OBJECTIVES

This review examines theoretical and empirical contributions to the literature on entrainment, with a particular focus on the physiological mechanisms underlying this phenomenon and its role in cognitive, motor, and affective functions. We also address the inconsistent terminology used in the literature and evaluate the range of measurement approaches used to assess entrainment phenomena. Finally, we propose a definition of "physiological entrainment" that emphasizes its role as a fundamental mechanism that encompasses rhythmic interactions between the body and its environment, to support information processing across bodily systems and to sustain adaptive motor responses.

METHODS

We reviewed the recent literature through the lens of the "embodied cognition" framework, offering a unified perspective on the phenomenon of physiological entrainment.

RESULTS

Evidence from the current literature suggests that physiological entrainment produces measurable effects, especially on neural oscillations, heart rate variability, and motor synchronization. Eventually, such physiological changes can impact cognitive processing, affective functioning, and motor coordination.

CONCLUSIONS

Physiological entrainment emerges as a fundamental mechanism underlying the mind-body connection. Entrainment-based interventions may be used to promote well-being by enhancing cognitive, motor, and affective functions, suggesting potential rehabilitative approaches to enhancing mental health.

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.

Direct current stimulation as a non-invasive therapeutic alternative for treating autonomic or non-autonomic neurological disorders affecting breathing

Direct current stimulation (DCS) is a non-invasive approach to stimulate the nervous system that is now considered a powerful tool for treating neurological diseases such as those affecting cognitive or locomotor functions. DCS, as applied clinically today, is an approach built on early uses in antiquity and knowledge gained over time. Its current use makes use of specific devices and takes into account knowledge of the mechanisms by which this approach modulates functioning of the nervous system at the cellular level. Over the last 20 years, although there are few studies, it has been shown that DCS can also modulate the breathing autonomic function. In this narrative review, after briefly providing the historical perspective and describing the principles and the main cellular and molecular effects, we summarize the currently available data regarding the modulation of ventilation, and propose that DCS could be used to treat autonomic or non-autonomic neurological disorders affecting breathing.

The contribution of periaqueductal gray in the regulation of physiological and pathological behaviors

Periaqueductal gray (PAG), an integration center for neuronal signals, is located in the midbrain and regulates multiple physiological and pathological behaviors, including pain, defensive and aggressive behaviors, anxiety and depression, cardiovascular response, respiration, and sleep-wake behaviors. Due to the different neuroanatomical connections and functional characteristics of the four functional columns of PAG, different subregions of PAG synergistically regulate various instinctual behaviors. In the current review, we summarized the role and possible neurobiological mechanism of different subregions of PAG in the regulation of pain, defensive and aggressive behaviors, anxiety, and depression from the perspective of the up-down neuronal circuits of PAG. Furthermore, we proposed the potential clinical applications of PAG. Knowledge of these aspects will give us a better understanding of the key role of PAG in physiological and pathological behaviors and provide directions for future clinical treatments.

AIR Hunger-Why Amygdala Seizures Suppress Breathing

Failure to Breathe Persists Without Air Hunger or Alarm Following Amygdala Seizures Harmata GI, Rhone AE, Kovach CK, Kumar S, Mowla MR, Sainju RK, Nagahama Y, Oya H, Gehlbach BK, Ciliberto MA, Mueller RN, Kawasaki H, Pattinson KT, Simonyan K, Davenport PW, Howard MA III, Steinschneider M, Chan AC, Richerson GB, Wemmie JA, Dlouhy BJ. JCI Insight . 2023;8(22):e172423. doi:10.1172/jci.insight.172423 Postictal apnea is thought to be a major cause of sudden unexpected death in epilepsy (SUDEP). However, the mechanisms underlying postictal apnea are unknown. To understand causes of postictal apnea, we used a multimodal approach to study brain mechanisms of breathing control in 20 patients (ranging from pediatric to adult) undergoing intracranial electroencephalography for intractable epilepsy. Our results indicate that amygdala seizures can cause postictal apnea. Moreover, we identified a distinct region within the amygdala where electrical stimulation was sufficient to reproduce prolonged breathing loss persisting well beyond the end of stimulation. The persistent apnea was resistant to rising CO2 levels, and air hunger failed to occur, suggesting impaired CO2 chemosensitivity. Using es-fMRI, a potentially novel approach combining electrical stimulation with functional MRI, we found that amygdala stimulation altered blood oxygen level-dependent (BOLD) activity in the pons/medulla and ventral insula. Together, these findings suggest that seizure activity in a focal subregion of the amygdala is sufficient to suppress breathing and air hunger for prolonged periods of time in the postictal period, likely via brainstem and insula sites involved in chemosensation and interoception. They further provide insights into SUDEP, may help identify those at greatest risk, and may lead to treatments to prevent SUDEP.

Failure to breathe persists without air hunger or alarm following amygdala seizures

Postictal apnea is thought to be a major cause of sudden unexpected death in epilepsy (SUDEP). However, the mechanisms underlying postictal apnea are unknown. To understand causes of postictal apnea, we used a multimodal approach to study brain mechanisms of breathing control in 20 patients (ranging from pediatric to adult) undergoing intracranial electroencephalography for intractable epilepsy. Our results indicate that amygdala seizures can cause postictal apnea. Moreover, we identified a distinct region within the amygdala where electrical stimulation was sufficient to reproduce prolonged breathing loss persisting well beyond the end of stimulation. The persistent apnea was resistant to rising CO2 levels, and air hunger failed to occur, suggesting impaired CO2 chemosensitivity. Using es-fMRI, a potentially novel approach combining electrical stimulation with functional MRI, we found that amygdala stimulation altered blood oxygen level-dependent (BOLD) activity in the pons/medulla and ventral insula. Together, these findings suggest that seizure activity in a focal subregion of the amygdala is sufficient to suppress breathing and air hunger for prolonged periods of time in the postictal period, likely via brainstem and insula sites involved in chemosensation and interoception. They further provide insights into SUDEP, may help identify those at greatest risk, and may lead to treatments to prevent SUDEP.

Protracted respiratory failure in a case of global spinal syringomyelia and Chiari malformation following administration of diazepam: illustrative case

BACKGROUND

Syringomyelia is defined as dilation of the spinal cord's central canal and is often precipitated by skull base herniation disorders. Although respiratory failure (RF) can be associated with skull base abnormalities due to brainstem compression, most cases occur in pediatric patients and quickly resolve. The authors report the case of an adult patient with global spinal syringomyelia and Chiari malformation who developed refractory RF after routine administration of diazepam.

OBSERVATIONS

A 31-year-old female presented with malnutrition, a 1-month history of right-sided weakness, and normal respiratory dynamics. After administration of diazepam prior to magnetic resonance imaging (MRI), she suddenly developed hypercapnic RF followed MRI and required intubation. MRI disclosed a Chiari malformation type I and syrinx extending from C1 to the conus medullaris. After decompressive surgery, her respiratory function progressively returned to baseline status, although 22 months after initial benzodiazepine administration, the patient continues to require nocturnal ventilation.

LESSONS

Administration of central nervous system depressants should be closely monitored in patients with extensive syrinx formation given the potential to exacerbate diminished central respiratory drive. Early identification of syrinx in the context of Chiari malformation and hemiplegia should prompt clinical suspicion of underlying respiratory compromise and early involvement of intensive care consultants.

Changes in respiratory structure and function after traumatic cervical spinal cord injury: observations from spinal cord and brain

Respiratory difficulties and mortality following severe cervical spinal cord injury (CSCI) result primarily from malfunctions of respiratory pathways and the paralyzed diaphragm. Nonetheless, individuals with CSCI can experience partial recovery of respiratory function through respiratory neuroplasticity. For decades, researchers have revealed the potential mechanism of respiratory nerve plasticity after CSCI, and have made progress in tissue healing and functional recovery. While most existing studies on respiratory plasticity after spinal cord injuries have focused on the cervical spinal cord, there is a paucity of research on respiratory-related brain structures following such injuries. Given the interconnectedness of the spinal cord and the brain, traumatic changes to the former can also impact the latter. Consequently, are there other potential therapeutic targets to consider? This review introduces the anatomy and physiology of typical respiratory centers, explores alterations in respiratory function following spinal cord injuries, and delves into the structural foundations of modified respiratory function in patients with CSCI. Additionally, we propose that magnetic resonance neuroimaging holds promise in the study of respiratory function post-CSCI. By studying respiratory plasticity in the brain and spinal cord after CSCI, we hope to guide future clinical work.

In light of breathing: environmental light is an important modulator of breathing with clinical implications

In vertebrate animals, the automatic, rhythmic pattern of breathing is a highly regulated process that can be modulated by various behavioral and physiological factors such as metabolism, sleep-wake state, activity level, and endocrine signaling. Environmental light influences many of these modulating factors both indirectly by organizing daily and seasonal rhythms of behavior and directly through acute changes in neural signaling. While several observations from rodent and human studies suggest that environmental light affects breathing, few have systematically evaluated the underlying mechanisms and clinical relevance of environmental light on the regulation of respiratory behavior. Here, we provide new evidence and discuss the potential neurobiological mechanisms by which light modulates breathing. We conclude that environmental light should be considered, from bench to bedside, as a clinically relevant modulator of respiratory health and disease.