Biology subjects

Barik, A.

Publications and source records attributed to Barik, A..

17 recordsLinked to original sources

bioRxiv2026

Intersectional genetic targeting of molecularly distinct melanin-concentrating hormone neuron subpopulations reveals distinct and overlapping subcircuit architecture

The lateral hypothalamic area (LHA) coordinates crucial and innate behaviors through heterogeneous yet poorly understood neuronal populations and circuits. Neurons that produce melanin-concentrating hormone (MCH; encoded by the Pmch gene) are primarily localized in the LHA and contribute to feeding, sleep-wake regulation, memory, and reward-associated behaviors. Building on foundational anatomical studies, our single-cell transcriptomic analysis of the LHA identified markers distinguishing at least two transcriptionally distinct MCH subpopulations. These subpopulations are distinguished by the selective enrichment of the Tacr3 and Cartpt transcripts, with each comprising approximately half of the total MCH population. However, these subpopulations remain poorly understood owing to limited genetic targeting tools. We hypothesized that MCH neurons operate through functionally distinct, parallel subcircuits that exhibit unique neuroanatomical projections. In this study, we leveraged Pmch and Tacr3 expression to intersectionally dissociate these neurons into Type I MCH (Pmch+/Tacr3+) and Type II MCH (Pmch+/Tacr3-) subpopulations. We first validated a Tacr3-Flpo mouse line for the genetic targeting of the Type I MCH subpopulation. We then generated an intersectional Type I MCH neuron reporter line to visualize Type I axonal projections. In parallel, we injected a dual recombinase mouse line with the intersectional genetic targeting viruses, Conditional Viral Expression by Ribozyme Guided Degradation (ConVERGD), and identified overlapping and distinct projections by Type I and Type II MCH neurons using fluorescence microscopy, super-resolution imaging, and high-spatial resolution fiber mapping. Overall, these data establish the first subpopulation-resolved anatomical framework for molecularly distinct Type I and Type II MCH subcircuits, thus establishing a foundation for future circuit-level functional studies.

neuroscience↗

bioRxiv2026

Regulation of itch-induced scratching by nucleus accumbens dopamine receptor-expressing neurons

Scratching provides transient relief from itch, yet the neural circuit mechanisms that transform scratching into itch relief remain poorly understood. Midbrain dopaminergic neurons and their downstream targets in the lateral shell of the nucleus accumbens (NAc LaSh) are implicated in itch-scratch processing. Previous studies show that pharmacological manipulation of dopamine D1 and D2 receptors in the NAc LaSh alters scratching behavior, but the specific contributions of D1R- and D2R-expressing neurons during acute and chronic itch remain unclear. Here, we show that NAc LaShD1R and D2R neurons bidirectionally regulate scratching behavior across itch states. NAc LaShD1R neurons activity promotes scratching bouts, whereas NAc LaShD2R neurons preferentially facilitate scratch termination. Anterograde viral tracing revealed distinct brain-wide projection patterns of NAc LaShD1R and D2R neurons, which we functionally tested using projection-specific optogenetic manipulations. We found that NAc LaShD2R neurons terminate scratching by inhibiting neurons in the lateral parabrachial nucleus (LPBN), a key hub for itch processing. Furthermore, dopamine levels in the NAc LaSh were elevated during chronic itch compared with acute itch, suggesting enhanced dopaminergic signaling contributes to persistent scratching. Together, these findings identify circuit mechanisms linking reward pathways to itch regulation.

neuroscience↗

bioRxiv2026

D1R-specific modulation of ACC mitigates chronic neuropathic pain

Maladaptive plasticity within central pain circuits is a defining feature of chronic neuropathic pain, yet the mechanisms governing these changes remain unclear. This study investigates the role of the mesocortical dopaminergic pathway in the neuropathic pain-induced hyperexcitability of dopamine D1 receptor-expressing anterior cingulate cortex (ACCD1R) neurons. We find that infusing D1R agonists in the ACC reverses the mechanical hypersensitivity and negative affective-motivational affect in mice caused by spared-nerve injury (SNI). Although ACC pyramidal neurons are widely presumed to be the principal targets of D1R signaling, ex vivo recordings reveal that D1R agonists suppress the excitability of D1R-expressing pyramidal neurons while enhancing the excitability of D1R-expressing interneurons. Consistently, gene-expression analyses show that D1R-expression is distributed across both excitatory and inhibitory ACC neurons. Furthermore, we demonstrate that the excitability of genetically labeled D1R pyramidal neurons is enhanced by SNI, whereas in interneurons, it is reduced. Chemogenetic manipulation demonstrates that activation of D1R neurons produces robust analgesic and anxiolytic effects, whereas inhibition worsens pain- and anxiety-related behaviours, indicating that inhibitory D1R neurons dominate population-level output. Circuit tracing further delineates diverse afferent and efferent connections linking ACCD1R neurons to sensory and affective pain pathways. Together, these results identify dopaminergic regulation of ACCD1R neurons as a critical determinant of cortical dysfunction in chronic pain.

neuroscience↗

bioRxiv2025

3D human skeletal muscle organoids reveal distinct effects of high-dose dihydronicotinamide riboside on muscle development

The evaluation of NAD+-boosting compounds in human skeletal muscle is hindered by limitations of traditional 2D cultures and animal models. Human-relevant, three-dimensional (3D) engineered skeletal muscle organoids offer a promising platform to assess the biological effects of metabolic modulation. Here we engineered 3D human skeletal muscle organoids to investigate the impact of dihydronicotinamide riboside (NRH), a potent NAD+ precursor. Sustained exposure to high NRH concentrations (500 {micro}M) enhanced early differentiation markers, including increased myotube fusion and fast-twitch fiber area, but concurrently induced structural defects such as disrupted sarcomeric organization, enlarged acetylcholine receptor clusters, and impaired acetylcholine-stimulated calcium signaling. These results reveal that excessive and sustained NAD+ elevation can uncouple rapid differentiation from proper maturation in muscle tissue. Our results highlight the importance of dose and duration optimization for NAD+-boosting compounds and establish 3D engineered muscle organoids as a valuable non-animal platform for mechanistic toxicology and preclinical safety assessment.

bioengineering↗

bioRxiv2025

Scratcher: An automated machine-vision tool for dissecting the neural basis of itch

Itch or pruritus invokes a specific reflexive and repetitive directed nocifensive behavioural response, known as scratching. Recent decades have revealed neural circuits that are involved in the sensory and affective-motivational aspects of itch-induced scratching. However, most of these studies relied on manual subjective methods of quantifying scratching in laboratory mice and rats. Recent advances in deep learning have opened avenues for the development of computational tools to analyze animal behaviour in a reliable and automated manner. Further, combined with optogenetic and chemogenetic strategies, these tools can accelerate our understanding of neural circuits underlying itch and scratching. To that end, we have developed Scratcher, a GUI-based computational tool based on a real-time object detection algorithm that allows semi-supervised automated analysis of scratching behaviour in mice in a computationally inexpensive manner. We recorded chloroquine-induced acute itch as it developed and determined the consequence of nail-trimming on acute-itch induced scratching with Scratcher. To probe the neural mechanisms underlying itch, we combined Scratcher with genetic circuit dissection using the Fos-TRAP mouse line. By targeting itch-activated neurons in the lateral parabrachial nucleus (LPBN) - a key brainstem hub for pruritic signal transmission - we demonstrated that LPBN activity modulates itch-evoked scratching. Together, we present a novel, easy-to-use computational tool to dissect molecular, cellular, and circuit mechanisms of itch and scratching.

neuroscience↗

bioRxiv2025

Lateral hypothalamus directs stress-induced modulation of acute and psoriatic itch

Stress and anxiety are well-known modulators of both physiological and pathological itch. Acute stress suppresses itch, while chronic stress exacerbates it. These effects are mediated by neural circuits within the brain, though the precise mechanisms remain poorly understood. In this study, we investigate the role of neurons in the stress-sensitive lateral hypothalamic area (LHA) in modulating itch. Using neural activity-dependent genetic labeling and chemogenetic tools, we selectively engaged a population of LHA neurons (LHAstress-TRAP neurons) responsive to stress. Transient stimulation of these neurons induced anxiety-like behaviors, conditioned place aversion, and suppressed acute (chloroquine-induced) and chronic (psoriatic) itch. Conversely, the inhibition of the LHAstress-TRAP neurons enhanced acute and chronic itch. Interestingly, LHAstress-TRAP neurons did not respond to acute itch stimuli, but their activity was temporally correlated with scratching episodes in mice with psoriasis. Ex vivo whole-cell patch-clamp recordings revealed that these neurons exhibit heightened excitability in psoriatic animals. Anterograde viral tracing demonstrated that LHAstress-TRAP neurons project to brainstem regions implicated in itch modulation, including the periaqueductal gray (PAG), rostral ventromedial medulla (RVM), and lateral parabrachial nucleus (LPBN). Furthermore, chemogenetic activation and optogenetic silencing of LHAstress-TRAP axon terminals revealed that bidirectional modulation of itch is primarily mediated through projections to the PAG. Together, these findings identify a previously unrecognized central mechanism by which stress modulates itch, centered on a specific population of LHA neurons and their downstream brainstem targets.

neuroscience↗

bioRxiv2025

A brainstem-thalamic circuitry for affective-motivational responses to cold pain

The medial thalamus is crucial for the sensory and affective-motivational responses to chronic pain. However, a mechanistic understanding of how the distinct subnuclei of the medial thalamus mediate behavioral responses to pain remains lacking. Taking advantage of intersectional viral genetics, chemogenetics, optogenetics, in-vivo imaging, and ex-vivo physiology, we reveal that the neurons in the parafascicular (PF) nuclei of the medial thalamus receive monosynaptic inputs from the lateral parabrachial nuclei (LPBN) in mice. LPBN is an essential nucleus in the ascending pain pathway, receiving projections from the dorsal horn of the spinal cord. The PF neurons downstream of LPBN (PFpost-LPBN) are nociceptive, sensitized by peripheral neuropathy, acutely aversive, and, when activated, drive both sensory and affective-motivational responses to cold pain. In contrast, the LPBN target neurons in the intralaminar centromedian thalamus (CMpost-LPBN), another nociceptive nucleus of the medial thalamus, are primarily involved in the affective-motivational aspects of pain. Together, we reveal that the LPBN, through two closely related thalamic nuclei, influences behavior in mice with cold hypersensitivity due to peripheral neuropathies.

neuroscience↗

bioRxiv2024

Acute restraint stress and pain modulation depend on the interaction between the periaqueductal gray and the lateral septum

Acute restraint stress is known to cause analgesia in humans and laboratory animals, but the mechanisms are unknown. Recently, we have shown that a multi-nodal circuitry between the dorsal lateral septum (dLS)-lateral hypothalamic area (LHA)-rostral ventromedial medulla (RVM) plays an instructive role in restraint stress-induced analgesia. We found that the LS neurons are activated when mice struggle to escape the restraint, and we wondered about the origin of the escape signals. Hence, we performed retrograde viral labeling from the LS and found that the ventrolateral periaqueductal gray (vlPAG), a known anatomical substrate for escape behaviors, provides inputs to the LS. Through anatomical, behavioral, and in-vivo fiber photometry, we show that the PAG and LS neurons are synaptically connected; activation of either PAG or the post-synaptic LS neurons is sufficient to cause analgesia and sufficiently cause hyperalgesia. Moreover, we found that the LS neurons that receive inputs from PAG send axonal projections to the LHA. Together, we found that the vlPAG neurons encoding nociceptive and escape behaviors provide synaptic inputs to the dLS-LHA-RVM circuitry to mediate acute restraint stress-induced analgesia. Significance statementForced restraint causes stress, and this paradigm has been used in the laboratory to study the physiological effects of stress, including pain modulation. The dorsal lateral septum (LS) has been shown to mediate restraint-mediated stress and analgesia. It is unknown what signals encoded in the LS allow it to instruct stress and pain. A novel neural pathway between the periaqueductal gray (PAG) and LS is activated when mice try to escape the restraint. Repeated activity in the PAG-LS circuitry due to the inescapability of the restraint causes stress and analgesia

neuroscience↗

bioRxiv2024

Rostral ventromedial medulla (RVM) projects to the lateral hypothalamic area (LHA) to drive aversion and anxiety

Neurons in the LHA are critical drivers of behavioral and physiological responses to acute and chronic stress. However, the roles of the specific pre-synaptic inputs to the LHA in driving stress and resultant physiological effects are yet to be fully understood. Here, taking advantage of mouse viral genetics, rabies tracing, optogenetics, chemogenetics, and fiber photometry, we show that the excitatory projections from the RVM to LHA drive stress-induced anxiety. This is a surprising finding since, traditionally, RVM has been studied in the context of opioidergic pain modulation through its inhibitory projections to the spinal cord. We find that the LHA neurons receiving inputs from the RVM, when activated, do not alter the nociceptive thresholds yet are sufficient to drive anxiety-like behaviors. These LHA neurons are recruited by acute restraint, which is known to cause stress. On the other hand, the LHA-projecting RVM neurons are responsive to both noxious thermal stimuli and acute restraint, promoting stress-induced anxiety, yet with no effect on pain thresholds. Together, we found an ascending neural pathway between RVM and LHA that mediates stress-induced anxiety. Significance statementThere is a strong correlation between pain and anxiety. However, the underlying neural mechanisms are poorly understood. Here, we reveal a novel neural pathway between the rostral ventromedial medulla (RVM) and lateral hypothalamus (LHA) that can potentially convert painful experiences into stress and anxiety. The traditional role of RVM is opioidergic modulation of pain. However, here we show that in addition to nociception, RVM neurons can play an essential role in the affective-motivational components of pain.

neuroscience↗

bioRxiv2024

An Intra-brainstem Circuit for Pain-induced Inhibition of Itch

Pain and itch are unpleasant and distinct sensations that give rise to behaviors such as reflexive withdrawal and scratching in humans and mice. Interestingly, it has been observed that pain modulate itch through the neural circuits housed in the brain and spinal cord. However, we are yet to fully understand the identities of and mechanisms by which specific neural circuits mediate pain-induced modulation of itch. Independent studies indicate that brainstem nuclei such as the lateral parabrachial nucleus (LPBN) and rostral ventromedial medulla (RVM) are important for the suppression of itch by painful stimuli. Here, using mouse and viral genetics, rabies tracing, chemogenetics, and calcium imaging, we show that the synaptic connections between LPBN and RVM plays an instrumental role in the interactions between pain and itch. Notably, we found that the LPBN neurons that express the gene encoding the substance P receptor, Tacr1 (LPBNTacr1), synapse onto Tacr1-expressing RVM neurons (RVMTacr1). The RVMTacr1 neurons were found to be nociceptive, sufficient for inhibiting itch, and necessary for pain-induced itch suppression. Moreover, through brain-wide anterograde and retrograde viral tracing studies, we found that the RVMTacr1 neurons are bidirectionally connected with LPBN, periaqueductal gray (PAG), and lateral hypothalamic area (LHA). Thus, together, our data indicate that the RVMTacr1 neurons integrate nociceptive information to mediate itch-induced scratching and can mediate the physiological effects of itch through their downstream targets.

neuroscience↗

bioRxiv2024

Converging inputs compete at the lateral parabrachial nuclei to dictate the affective-motivational responses to cold pain

The neural mechanisms of the affective-motivational symptoms of chronic pain are poorly understood. In chronic pain, our innate coping mechanisms fail to provide relief leading to heightened manifestation of these behaviors. In laboratory animals, such as mice and rats, licking the affected areas is a behavioral coping mechanism and it is sensitized in chronic pain. Hence, we have focused on delineating the brain circuits mediating licking in mice with chemotherapy-induced peripheral neuropathy (CIPN). Mice with CIPN develop intense cold hypersensitivity and lick their paws upon contact with cold stimuli. We studied how the lateral parabrachial nucleus (LPBN) neurons facilitate licking behavior when mice are exposed to noxious thermal stimuli. Taking advantage of transsynaptic viral, optogenetic, and chemogenetic strategies, we observed that the LPBN neurons become hypersensitive to cold in mice with CIPN and facilitate licks. Further, we found that the expression of licks depends on competing excitatory and inhibitory inputs from the spinal cord and lateral hypothalamus (LHA), respectively. We anatomically traced the post-synaptic targets of the spinal cord and LHA in the LPBN and found that they synapse onto overlapping populations. Activation of this LPBN population was sufficient to promote licking due to cold allodynia. In sum, our data indicate that the nociceptive inputs from the spinal cord and information on brain states from the hypothalamus impinge on overlapping LPBN populations to modulate their activity and, in turn, regulate the elevated affective-motivational responses in CIPN.

neuroscience↗

bioRxiv2023

Senescent cells inhibit muscle differentiation via the lipid- SASP 15d-PGJ2 mediated modification and control of HRas

Senescent cells, which are characterized by multiple features such as increased expression of Senescence-Associated {beta}-galactosidase activity (SA {beta}-gal) and cell cycle inhibitors such as p21 or p16, accumulate with tissue damage and dysregulate tissue homeostasis. In the context of skeletal muscle, it is known that agents used for chemotherapy such as Doxorubicin cause buildup of senescent cells, leading to the inhibition of tissue regeneration. Senescent cells influence the neighboring cells via numerous secreted factors which form the senescence-associated secreted phenotype (SASP). Lipids are emerging as a key component of SASP that can control tissue homeostasis. Arachidonic acid-derived lipids have been shown to accumulate within senescent cells, specifically 15d-PGJ2, which is an electrophilic lipid produced by the non-enzymatic dehydration of the prostaglandin PGD2. In this study, we show that 15d-PGJ2 is also released by Doxorubicin-induced senescent cells as a SASP factor. Treatment of skeletal muscle myoblasts with the conditioned medium from these senescent cells inhibits myoblast fusion during differentiation. Inhibition of L-PTGDS, the enzyme that synthesizes PGD2, diminishes the release of 15d-PGJ2 by senescent cells and restores muscle differentiation. We further show that this lipid post-translationally modifies Cys184 of HRas in skeletal muscle cells, causing a reduction in the localization of HRas to the Golgi, increased HRas binding to RAF RBD, and activation of cellular MAPK-Erk signaling (but not the Akt signaling). Mutating C184 of HRas prevents the ability of 15d- PGJ2 to inhibit the differentiation of muscle cells and control the activity of HRas. This work shows that 15d-PGJ2 released from senescent cells could be targeted to restore muscle homeostasis after chemotherapy.

biochemistry↗

bioRxiv2023

C-terminal cysteines of HRas control Erk signaling and 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) mediated inhibition of myoblast differentiation.

HRas is an important node that controls cellular signaling, proliferation, and differentiation. Mutants of HRas (e.g., the constitutively active HRas V12) can be oncogenic, and can also inhibit myoblast differentiation. The C-terminal cysteines of HRas (Cys181 and Cys184) serve as substrates for intra-cellular reversible palmitoylation and de-palmitoylation reactions, which control its subcellular distribution. The relationship between the C-terminal cysteines of HRas, its intracellular distribution, and its cellular activity has remained unclear. Understanding this relationship has important implications for targeting HRas in pathogenic states where it is activated. In this study, we show that a mutation in the C-terminal of HRas, C181S, is sufficient to cause increased levels of HRas V12 in the Golgi, decreased HRas V12-driven Akt and Erk signaling and reverse the ability of HRas V12 to inhibit myoblast differentiation. This demonstrates the importance of C-terminal cysteines in controlling HRas V12. It has been previously shown that Cys184 can also be irreversibly modified by an electrophilic prostaglandin lipid 15d-PGJ2. This lipid is released by senescent cells as a part of senescence-associated secretory phenotype (SASP). In this study, we show that 15d-PGJ2 is secreted by senescent myoblasts formed by treatment with Doxorubicin. We also show that 15d-PGJ2 causes decreased levels of HRas within Golgi, activates Erk signaling (but not Akt signaling), and inhibits differentiation of C2C12 myoblasts in an HRas Cys184-dependent fashion. Chemotherapeutics such as Doxorubicin drive senescence and loss of skeletal muscle homeostasis in cancer patients. This study suggests that targeting the senescence-derived synthesis of 15-PGJ2 might be a target to promote muscle homeostasis after chemotherapy.

cell biology↗

bioRxiv2023

A deep-learning driven investigation of circuit basis for reflexive hypersensitivity to pain

Objectively measuring animal behavior is key to understanding the neural circuits underlying pain. Recent progress in machine vision has presented us with unprecedented scope in behavioral analysis. Here, we apply DeeplabCut (DLC) to dissect mouse behavior on the thermal-plate test -- a commonly used paradigm to ascertain supraspinal contributions to noxious thermal sensation and pain hypersensitivity. We determine the signature characteristics of the pattern of mouse movement and posture in 3D in response to a range of temperatures from innocuous to noxious on the thermal-plate test. Next, we test how acute chemical and chronic inflammatory injuries sensitize mouse behaviors. Repeated exposure to noxious temperatures on the thermal-plate can induce learning, and in this study, we design a novel assay and formulate an analytical pipeline that will facilitate the dissection of plasticity mechanisms in pain circuits in the brain. Last, we record and test how activating Tacr1 expressing PBN neurons -- a population responsive to sustained noxious stimuli-affects mouse behavior on the thermal plate test. Taken together, we demonstrate that by tracking a single body part of a mouse, we can reveal the behavioral signatures of mice exposed to noxious surface temperatures, report the alterations of the same when injured, and determine if a molecularly and anatomically defined pain responsive circuit plays a role in the reflexive hypersensitivity to thermal pain.

neuroscience↗

bioRxiv2023

The lateral septum plays a transforming role in acute stress-induced analgesia

AbstractStress is a potent modulator of pain. Specifically, acute stress due to physical restraint induces stress-induced analgesia (SIA). However, where and how acute stress and pain pathways interface in the brain are poorly understood. Here, we describe how the dorsal lateral septum (dLS), a forebrain limbic nucleus, facilitates SIA through its downstream targets in the lateral hypothalamic area (LHA) of mice. Taking advantage of transsynaptic viral-genetic, optogenetic, and chemogenetic techniques, we show that the dLS[->]LHA circuitry is sufficient to drive analgesia and is required for SIA. Further, our results reveal that the dLS[->]LHA pathway is opioid-dependent and modulates pain through the pro-nociceptive neurons in the rostral ventromedial medulla (RVM). Remarkably, we found that the inhibitory dLS neurons are recruited specifically when the mice struggle to escape under restraint and, in turn, inhibit excitatory LHA neurons. As a result, the RVM neurons downstream of LHA are disengaged, thus suppressing nociception. Together, we delineate a poly-synaptic pathway that can transform escape behavior in mice under restraint to acute stress into analgesia.

neuroscience↗

bioRxiv2020

South Asian patient population genetics reveal strong founder effects and high rates of homozygosity - new resources for precision medicine

Population-scale genetic studies can identify drug targets and allow disease risk to be predicted with resulting benefit for management of individual health risks and system-wide allocation of health care delivery resources. Although population-scale projects are underway in many parts of the world, genetic variation between population groups means that additional projects are warranted. South Asia has a population whose genetics is the least characterized of any of the worlds major populations. Here we describe GenomeAsia studies that characterize population structure in South Asia and that create tools for economical and accurate genotyping at population-scale. Prior work on population structure characterized isolated population groups, the relevance of which to large-scale studies of disease genetics is unclear. For our studies we used whole genome sequence information from 4,807 individuals recruited in the health care delivery systems of Pakistan, India and Bangladesh to ensure relevance to population-scale studies of disease genetics. We combined this with WGS data from 927 individuals from isolated South Asian population groups, and developed a custom SNP array (called SARGAM) that is optimized for future human genetic studies in South Asia. We find evidence for high rates of reproductive isolation, endogamy and consanguinity that vary across the subcontinent and that lead to levels of homozygosity that approach 100 times that seen in outbred populations. We describe founder effects that increase the power to associate functional variants with disease processes and that make South Asia a uniquely powerful place for population-scale genetic studies.

genomics↗

bioRxiv2020

A spinoparabrachial circuit defined by Tacr1 expression drives pain

Painful stimuli evoke a mixture of sensations, negative emotions and behaviors. These myriad effects are thought to be produced by parallel ascending circuits working in combination. Here we describe a pathway from spinal cord to brain for ongoing pain. Activation of a defined subset of spinal projection neurons expressing Tacr1 evokes a full repertoire of somatotopically-directed coping behaviors in the absence of noxious input. These cells project to a tiny cluster of Tacr1-positive neurons in the superior lateral parabrachial nucleus (PBN-SL) that themselves are responsive to sustained but not acute noxious stimuli. Activation of these PBN-SLTacr1 neurons alone does not trigger pain responses but instead serves to dramatically heighten nocifensive behaviors and suppress itch. Remarkably, mice with silenced PBN-SLTacr1 neurons ignore long-lasting noxious stimuli. These data reveal a spinoparabrachial pathway that plays a key role in the sensation of ongoing pain.

neuroscience↗