Regional hypothalamic, amygdala, and midbrain periaqueductal gray matter recruitment during acute pain in awake humans: A 7-Tesla functional magnetic resonance imaging study

Differential activation of lateral parabrachial nuclei and their limbic projections during head compared with body pain: A 7-Tesla functional magnetic resonance imaging study

Pain is a complex experience that involves sensory, emotional, and motivational components. It has been suggested that pain arising from the head and orofacial regions evokes stronger emotional responses than pain from the body. Indeed, recent work in rodents reports different patterns of activation in ascending pain pathways during noxious stimulation of the skin of the face when compared to noxious stimulation of the body. Such differences may dictate different activation patterns in higher brain regions, specifically in those areas processing the affective component of pain. We aimed to use ultra-high field functional magnetic resonance imaging (fMRI at 7-Tesla) to determine whether noxious thermal stimuli applied to the surface of the face and body evoke differential activation patterns within the ascending pain pathway in awake humans (n=16). Compared to the body, noxious heat stimulation to the face evoked more widespread signal changes in prefrontal cortical regions and numerous brainstem and subcortical limbic areas. Moreover, facial pain evoked significantly different signal changes in the lateral parabrachial nucleus, substantia nigra, paraventricular hypothalamus, and paraventricular thalamus, to those evoked by body pain. These results are consistent with recent preclinical findings of differential activation in the brainstem and subcortical limbic nuclei and associated cortices during cutaneous pain of the face when compared with the body. The findings suggest one potential mechanism by which facial pain could evoke a greater emotional impact than that evoked by body pain.

A Hypothalamic Perspective of Human Socioemotional Behavior

Historical evidence from stimulation and lesion studies in animals and humans demonstrated a close association between the hypothalamus and typical and atypical socioemotional behavior. A central hypothalamic contribution to regulation of socioemotional responses was also provided indirectly by studies on oxytocin and arginine vasopressin. However, a limited number of studies have so far directly investigated the contribution of the hypothalamus in human socioemotional behavior. To reconsider the functional role of the evolutionarily conserved hypothalamic region in regulating human social behavior, here I provide a synthesis of neuroimaging investigations showing that the hypothalamus is involved in multiple and diverse facets of human socioemotional behavior through widespread functional interactions with other cortical and subcortical regions. These neuroimaging findings are then integrated with recent optogenetics studies in animals demonstrating that the hypothalamus plays a more active role in eliciting socioemotional responses and is not simply a downstream effector of higher-level brain systems. Building on the aforementioned evidence, the hypothalamus is argued to substantially contribute to a continuum of human socioemotional behaviors promoting survival and preservation of the species that extends from exploratory and approaching responses facilitating social bonding to aggressive and avoidance responses aimed to protect and defend formed relationships.

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.

Endocrinology-informed neuroimaging in eating disorders: GLP1, orexins, and psilocybin

The neurobiology of eating disorders [EDs; anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED)] remains poorly understood. Here, I describe how neuroimaging, accompanied by peripheral endocrine measures, can provide insights into the neurobiological drivers of eating disorders. Orexins/hypocretins, glucagon-like peptide-1 receptor (GLP1R) agonists, and psilocybin are highlighted as avenues for investigation.

Assessment of brainstem function and haemodynamics by MRI: challenges and clinical prospects

MRI offers techniques for non-invasively measuring a range of aspects of brain tissue function. Blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) is widely used to assess neural activity, based on the brain's haemodynamic response, while arterial spin labelling (ASL) MRI is a non-invasive method of quantitatively mapping cerebral perfusion. Both techniques can be applied to measure cerebrovascular reactivity (CVR), an important marker of the health of the cerebrovascular system. BOLD, ASL and CVR have been applied to study a variety of disease processes and are already used in certain clinical circumstances. The brainstem is a critical component of the central nervous system and is implicated in a variety of disease processes. However, its function is difficult to study using MRI because of its small size and susceptibility to physiological noise. In this article, we review the physical and biological underpinnings of BOLD and ASL and their application to measure CVR, discuss the challenges associated with applying them to the brainstem and the opportunities for brainstem MRI in the research and clinical settings. With further optimisation, functional MRI techniques could feasibly be used to assess brainstem haemodynamics and neural activity in the clinical setting.

Ultra-high field imaging of the amygdala - A narrative review

The amygdala is an evolutionarily conserved core structure in emotion processing and one of the key regions of interest in affective neuroscience. Results of neuroimaging studies focusing on the amygdala are, however, often heterogeneous since it is composed of functionally and neuroanatomically distinct subnuclei. Fortunately, ultra-high-field imaging offers several advances for amygdala research, most importantly more accurate representation of functional and structural properties of subnuclei and their connectivity. Most clinical studies using ultra-high-field imaging focused on major depression, suggesting either overall rightward amygdala atrophy or distinct bilateral patterns of subnuclear atrophy and hypertrophy. Other pathologies are only sparsely covered. Connectivity analyses identified widespread networks for learning and memory, stimulus processing, cognition, and social processes. They provide evidence for distinct roles of the central, basal, and basolateral nucleus, and the extended amygdala in fear and emotion processing. Amid largely sparse and ambiguous evidence, we propose theoretical and methodological considerations that will guide ultra-high-field imaging in comprehensive investigations to help disentangle the ambiguity of the amygdala's function, structure, connectivity, and clinical relevance.

The Underlying Mechanisms of Sleep Deprivation Exacerbating Neuropathic Pain

Pain disrupts sleep, and sleep deprivation or interference can alter pain perception in animals and humans, for example by increasing sensitivity to pain. However, the mechanism by which sleep affects neuropathic pain remains unclear. In this review, we discuss the available evidence from the epidemiologic, clinical, and human, as well as laboratory studies. In previous studies, we have found that sleep deprivation affects various injurious systems, including opioids, dopaminergic, immune, orexins, hypothalamic-pituitary-adrenal axis, and adenosine. At the same time, these systems play a crucial role in neuropathic pain regulation. In the complex interactions between these neurobiological systems, there may be potential regulatory pathways through which sleep deprivation amplifies neuropathic pain. Because of the impact sleep problems and neuropathic pain can have on the patients' quality of life, studying the link between sleep and neuropathic pain is important for neuropathic pain prevention and public health.

Resting state functional connectivity differentiation of neuropathic and nociceptive pain in individuals with chronic spinal cord injury

Many individuals with spinal cord injury live with debilitating chronic pain that may be neuropathic, nociceptive, or a combination of both in nature. Identification of brain regions demonstrating altered connectivity associated with the type and severity of pain experience may elucidate underlying mechanisms, as well as treatment targets. Resting state and sensorimotor task-based magnetic resonance imaging data were collected in 37 individuals with chronic spinal cord injury. Seed-based correlations were utilized to identify resting state functional connectivity of regions with established roles in pain processing: the primary motor and somatosensory cortices, cingulate, insula, hippocampus, parahippocampal gyri, thalamus, amygdala, caudate, putamen, and periaqueductal gray matter. Resting state functional connectivity alterations and task-based activation associated with individuals' pain type and intensity ratings on the International Spinal Cord Injury Basic Pain Dataset (0-10 scale) were evaluated. We found that intralimbic and limbostriatal resting state connectivity alterations are uniquely associated with neuropathic pain severity, whereas thalamocortical and thalamolimbic connectivity alterations are associated specifically with nociceptive pain severity. The joint effect and contrast of both pain types were associated with altered limbocortical connectivity. No significant differences in task-based activation were identified. These findings suggest that the experience of pain in individuals with spinal cord injury may be associated with unique alterations in resting state functional connectivity dependent upon pain type.

Assessment and management of pain/nociception in patients with disorders of consciousness or locked-in syndrome: A narrative review

The assessment and management of pain and nociception is very challenging in patients unable to communicate functionally such as patients with disorders of consciousness (DoC) or in locked-in syndrome (LIS). In a clinical setting, the detection of signs of pain and nociception by the medical staff is therefore essential for the wellbeing and management of these patients. However, there is still a lot unknown and a lack of clear guidelines regarding the assessment, management and treatment of pain and nociception in these populations. The purpose of this narrative review is to examine the current knowledge regarding this issue by covering different topics such as: the neurophysiology of pain and nociception (in healthy subjects and patients), the source and impact of nociception and pain in DoC and LIS and, finally, the assessment and treatment of pain and nociception in these populations. In this review we will also give possible research directions that could help to improve the management of this specific population of severely brain damaged patients.