Static and dynamic autonomic response with increasing nausea perception

Adverse Effects of Meditation: Autonomic Nervous System Activation and Individual Nauseous Responses During Samadhi Meditation in the Czech Republic

Buddhist meditation practices, including Samadhi meditation, which forms the basis for mindfulness practice, are broadly promoted as pathways to wellbeing, but evidence of their adverse effects is emerging. In a single-group observational study with assessments of autonomic system before, during, and after Samadhi meditation, we explore the relationship between post-meditation nausea symptoms and the degree of change in autonomic system activity during meditation as compared to before and after in 57 university students (42 women; mean age = 22.6) without any previous experience in meditation or yoga practices. We hypothesize that nauseous feelings in meditation are connected to a rapid increase of activity in the sympathetic nervous system, as indicated by decreased heart-rate variability (HRV). We additionally explore links between meditation-induced nausea and two markers of parasympathetic activity: increased HRV and vasovagal syncope. Engaging in meditation and increased nausea during meditation were both associated with increased markers of HRV parasympathetic activity, but 12 individuals with markedly higher nausea demonstrated increased HRV markers of sympathetic activity during meditation. Vasovagal syncope was observed but found to be unrelated to nausea levels. Drivers of adverse effects of meditation in some individuals require further investigation.

Transcutaneous Auricular Vagus Nerve Stimulation for Visually Induced Motion Sickness: An eLORETA Study

Transcutaneous auricular vagus nerve stimulation (taVNS), a non-invasive form of electrical brain stimulation, has shown potent therapeutic potential for a wide spectrum of conditions. How taVNS influences the characterization of motion sickness - a long mysterious syndrome with a polysymptomatic onset - remains unclear. Here, to examine taVNS-induced effects on brain function in response to motion-induced nausea, 64-channel electroencephalography (EEG) recordings from 42 healthy participants were analyzed; collected during nauseogenic visual stimulation concurrent with taVNS administration, in a crossover randomized sham-controlled study. Cortical neuronal generators were estimated from the obtained EEG using exact low-resolution brain electromagnetic tomography (eLORETA). While both sham and taVNS increased insula activation during electrical stimulation, compared to baseline, taVNS additionally augmented middle frontal gyrus neuronal activity. Following taVNS, brain regions including the supramarginal, parahippocampal, and precentral gyri were activated. Contrasting sham, taVNS markedly increased activity in the middle occipital gyrus during stimulation. A repeated-measures ANOVA showed that taVNS reduced motion sickness symptoms. This reduction in symptoms correlated with taVNS-induced neural activation. Our findings provide new insights into taVNS-induced brain changes, during and after nauseogenic stimuli exposure, including accompanying behavioral response. Together, these findings suggest that taVNS has promise as an effective neurostimulation tool for motion sickness management.

Physiological changes associated with copper sulfate-induced nausea and retching in felines

Nausea is a common disease symptom, yet there is no consensus regarding its physiological markers. In contrast, the process of vomiting is well documented as sequential muscular contractions of the diaphragm and abdominal muscles and esophageal shortening. Nausea, like other self-reported perceptions, is difficult to distinguish in preclinical models, but based on human experience emesis is usually preceded by nausea. Here we focused on measuring gastrointestinal and cardiorespiratory changes prior to emesis to provide additional insights into markers for nausea. Felines were instrumented to chronically record heart rate, respiration, and electromyographic (EMG) activity from the stomach and duodenum before and after intragastric delivery of saline or copper sulfate (CuSO4, from 83 to 322 mg). CuSO4 is a prototypical emetic test agent that triggers vomiting primarily by action on GI vagal afferent fibers when administered intragastrically. CuSO4 infusion elicited a significant increase in heart rate, decrease in respiratory rate, and a disruption of gastric and intestinal EMG activity several minutes prior to emesis. The change in EMG activity was most consistent in the duodenum. Administration of the same volume of saline did not induce these effects. Increasing the dose of CuSO4 did not alter the physiologic changes induced by the treatment. It is postulated that the intestinal EMG activity was related to the retrograde movement of chyme from the intestine to the stomach demonstrated to occur prior to emesis by other investigators. These findings suggest that monitoring of intestinal EMG activity, perhaps in combination with heart rate, may provide the best indicator of the onset of nausea following treatments and in disease conditions, including GI disease, associated with emesis.

Synergistic augmentation of rhythmic myogenic contractions of human stomach by arginine vasopressin and adrenaline: Implications for the induction of nausea

BACKGROUND AND PURPOSE

Nausea is associated with the hormonal secretion of vasopressin and adrenaline, although their actions in inducing nausea is poorly understood. Here, we have investigated their actions on human stomach muscle.

EXPERIMENTAL APPROACH

Muscle strips were suspended in tissue baths and neuronal-/non-neuronally-mediated contractions were measured. Custom software analysed eight motility parameters defining spontaneous phasic non-neuronally mediated contractions. Receptor distributions were assessed by qPCR and immunofluorescence.

KEY RESULTS

V_1A receptors and α₁ -adrenoceptors were located on muscle as well as interstitial cells of Cajal (ICCs). Myogenic contractions of human proximal and distal stomach (respectively, 2.6 ± 0.1 and 2.7 ± 0.0 per minute; n = 44) were larger in the distal area (1.1 ± 0.1 and 5.0 ± 0.1 mN), developing relatively slowly (proximal) or rapidly (distal). Vasopressin caused tonic (proximal) or short-lived (distal) increases in muscle tone and increased myogenic contraction amplitude, frequency and rate (acting at V_1A receptors; thresholds 10^-11 -10^-10  M); by contrast, cholinergically mediated contractions were unaffected. Oxytocin acted similarly to vasopressin but less potently, at OT receptors). Adrenaline increased (10^-10 -10^-5  M; α₁ -adrenoceptors) and decreased (≥10^-6  M; β-adrenoceptors) muscle tone and enhanced/reduced myogenic contractions. Cholinergically mediated contractions were reduced (α₂ -adrenoceptors). Combined, vasopressin (10^-9  M) and adrenaline (10^-8  M) increased muscle tone and phasic myogenic activity in a synergistic manner.

CONCLUSIONS AND IMPLICATIONS

Vasopressin and adrenaline increased human gastric tone and myogenic contraction amplitude, rate of contraction and frequency. In combination, their actions were further increased in a synergistic manner. Such activity may promote nausea.

Functional Nausea Is Real and Makes You Sick

Functional nausea is a condition that severely impairs the quality of life of affected individuals. Only recently, it has been added to the pediatric list of disorders of gut-brain interaction. In most cases, only minimal testing is needed to diagnose functional nausea. Hypnotherapy has been shown to be a very effective treatment and there are several other medical and non-medical interventions which have the potential to benefit sub-groups of patients with chronic nausea.

Profiling subjective symptoms and autonomic changes associated with cybersickness

Our aim was to expand knowledge of cybersickness - a subtype of motion sickness provoked by immersion into a moving computer-generated virtual reality. Fourteen healthy subjects experienced a 15-min rollercoaster ride presented via a head-mounted display (Oculus Rift), for 3 consecutive days. Heart rate, respiration, finger and forehead skin conductance were measured during the experiment; this was complemented by a subjective nausea rating during the ride and by Motion Sickness Assessment Questionnaire before, immediately after and then 1, 2 and 3h post-ride. Physiological measurements were analysed in three dimensions: ride time, association with subjective nausea rating and experimental day. Forehead, and to a lesser extent finger phasic skin conductance activity showed a correlation with the reported nausea ratings, while alteration in other measured parameters were mostly related to autonomic arousal during the virtual ride onset. A significant habituation was observed in subjective symptom scores and in the duration of tolerated provocation. The latter increased from 7.0±1.3min on the first day to 12.0±2.5min on the third day (p<0.05); this was associated with a reduced slope of nausea rise from 1.3±0.3units/min on the first to 0.7±0.1units/min on the third day (p<0.01). Furthermore, habituation with repetitive exposure was also determined in the total symptom score post-ride: it fell from 1.6±0.1 on the first day to 1.2±0.1 on the third (p<0.001). We conclude that phasic changes of skin conductance on the forehead could be used to objectively quantify nausea; and that repetitive exposure to provocative VR content results in habituation.

Motion sickness increases functional connectivity between visual motion and nausea-associated brain regions

The brain networks supporting nausea not yet understood. We previously found that while visual stimulation activated primary (V1) and extrastriate visual cortices (MT+/V5, coding for visual motion), increasing nausea was associated with increasing sustained activation in several brain areas, with significant co-activation for anterior insula (aIns) and mid-cingulate (MCC) cortices. Here, we hypothesized that motion sickness also alters functional connectivity between visual motion and previously identified nausea-processing brain regions. Subjects prone to motion sickness and controls completed a motion sickness provocation task during fMRI/ECG acquisition. We studied changes in connectivity between visual processing areas activated by the stimulus (MT+/V5, V1), right aIns and MCC when comparing rest (BASELINE) to peak nausea state (NAUSEA). Compared to BASELINE, NAUSEA reduced connectivity between right and left V1 and increased connectivity between right MT+/V5 and aIns and between left MT+/V5 and MCC. Additionally, the change in MT+/V5 to insula connectivity was significantly associated with a change in sympathovagal balance, assessed by heart rate variability analysis. No state-related connectivity changes were noted for the control group. Increased connectivity between a visual motion processing region and nausea/salience brain regions may reflect increased transfer of visual/vestibular mismatch information to brain regions supporting nausea perception and autonomic processing. We conclude that vection-induced nausea increases connectivity between nausea-processing regions and those activated by the nauseogenic stimulus. This enhanced low-frequency coupling may support continual, slowly evolving nausea perception and shifts toward sympathetic dominance. Disengaging this coupling may be a target for biobehavioral interventions aimed at reducing motion sickness severity.

Central Aspects of Nausea and Vomiting in GI Disorders

OPINION STATEMENT

Nausea and vomiting result from continuous interactions among gastrointestinal, central nervous system, and autonomic nervous system. Despite being closely associated, central pathways of nausea and vomiting appear to be at least partly different and nausea is no longer considered only a penultimate step of vomiting. Although our understanding of central pathways of nausea has improved over the last one decade, it is still very basic. Afferent pathways from gastrointestinal tract via vagus, vestibular system, and chemoreceptor trigger zone project to nucleus tractus solitarius which, in turn, relays the signal to central pattern generator initiating multiple downstream pathways. This central nausea pathway appears to be under constant modulation by autonomic nervous system and cerebral cortex. There is also some evidence that central pathway of chronic nausea is different from that of acute nausea and closely resembles that of neuropathic pain. This improved understanding has modified the way we can approach the treatment of acute and chronic nausea. While conventional therapies such as antiemetics (antiserotoninergic, antihistaminic, antidopaminergic) and prokinetics are commonly used to manage acute nausea, they are not as effective in improving chronic nausea. Recently, neuromodulators such as tricyclic antidepressants, gabapentin, olanzapine, benzodiazepines, and cannabinoids have been shown to have antinausea effect. There is a need to study the utility of these drugs in managing chronic functional nausea. Improving our understanding of central and peripheral circuitry of nausea will allow us to better utilize the currently available drugs and develop new therapeutic options.

What is nausea? A historical analysis of changing views

The connotation of "nausea" has changed across several millennia. The medical term 'nausea' is derived from the classical Greek terms ναυτια and ναυσια, which designated the signs and symptoms of seasickness. In classical texts, nausea referred to a wide range of perceptions and actions, including lethargy and disengagement, headache (migraine), and anorexia, with an awareness that vomiting was imminent only when the condition was severe. However, some recent articles have limited the definition to the sensations that immediately precede emesis. Defining nausea is complicated by the fact that it has many triggers, and can build-up slowly or rapidly, such that the prodromal signs and symptoms can vary. In particular, disengagement responses referred to as the "sopite syndrome" are typically present only when emetic stimuli are moderately provocative, and do not quickly culminate in vomiting or withdrawing from the triggering event. This review considers how the definition of "nausea" has evolved over time, and summarizes the physiological changes that occur prior to vomiting that may be indicative of nausea. Also described are differences in the perception of nausea, as well as the accompanying physiological responses, that occur with varying stimuli. This information is synthesized to provide an operational definition of nausea.

Nausea: a review of pathophysiology and therapeutics

The sensation of nausea is a common occurrence with diverse causes and a significant disease burden. Nausea is considered to function as a protective mechanism, warning the organism to avoid potential toxic ingestion. Less adaptive circumstances are also associated with nausea, including post-operative nausea, chemotherapy-induced nausea, and motion sickness. A common definition of nausea identifies the symptom as a precursor to the act of vomiting. The interaction, though present, does not appear to be a simple relationship. Nausea is unfortunately the 'neglected symptom', with current accepted therapy generally directed at improving gastrointestinal motility or acting to relieve emesis. Improved understanding of the pathophysiological basis of nausea has important implications for exploiting novel mechanisms or developing novel therapies for nausea relief.

Endocannabinoid Mechanisms Influencing Nausea

One of the first recognized medical uses of Δ(9)-tetrahydrocannabinol was treatment of chemotherapy-induced nausea and vomiting. Although vomiting is well controlled with the currently available non-cannabinoid antiemetics, nausea continues to be a distressing side effect of chemotherapy and other disorders. Indeed, when nausea becomes conditionally elicited by the cues associated with chemotherapy treatment, known as anticipatory nausea (AN), currently available antiemetics are largely ineffective. Considerable evidence demonstrates that the endocannabinoid system regulates nausea in humans and other animals. In this review, we describe recent evidence suggesting that cannabinoids and manipulations that enhance the functioning of the natural endocannabinoid system are promising treatments for both acute nausea and AN.

Endocannabinoid regulation of nausea is mediated by 2-arachidonoylglycerol (2-AG) in the rat visceral insular cortex

Cannabinoid (CB) agonists suppress nausea in humans and animal models; yet, their underlying neural substrates remain largely unknown. Evidence suggests that the visceral insular cortex (VIC) plays a critical role in nausea. Given the expression of CB1 receptors and the presence of endocannabinoids in this brain region, we hypothesized that the VIC endocannabinoid system regulates nausea. In the present study, we assessed whether inhibiting the primary endocannabinoid hydrolytic enzymes in the VIC reduces acute lithium chloride (LiCl)-induced conditioned gaping, a rat model of nausea. We also quantified endocannabinoid levels during an episode of nausea, and assessed VIC neuronal activation using the marker, c-Fos. Local inhibition of monoacylglycerol lipase (MAGL), the main hydrolytic enzyme of 2-arachidonylglycerol (2-AG), reduced acute nausea through a CB1 receptor mechanism, whereas inhibition of fatty acid amide hydrolase (FAAH), the primary catabolic enzyme of anandamide (AEA), was without effect. Levels of 2-AG were also selectively elevated in the VIC during an episode of nausea. Inhibition of MAGL robustly increased 2-AG in the VIC, while FAAH inhibition had no effect on AEA. Finally, we demonstrated that inhibition of MAGL reduced VIC Fos immunoreactivity in response to LiCl treatment. Taken together, these findings provide compelling evidence that acute nausea selectively increases 2-AG in the VIC, and suggests that 2-AG signaling within the VIC regulates nausea by reducing neuronal activity in this forebrain region.

Cybersickness provoked by head-mounted display affects cutaneous vascular tone, heart rate and reaction time

Evidence from studies of provocative motion indicates that motion sickness is tightly linked to the disturbances of thermoregulation. The major aim of the current study was to determine whether provocative visual stimuli (immersion into the virtual reality simulating rides on a rollercoaster) affect skin temperature that reflects thermoregulatory cutaneous responses, and to test whether such stimuli alter cognitive functions. In 26 healthy young volunteers wearing head-mounted display (Oculus Rift), simulated rides consistently provoked vection and nausea, with a significant difference between the two versions of simulation software (Parrot Coaster and Helix). Basal finger temperature had bimodal distribution, with low-temperature group (n=8) having values of 23-29 °C, and high-temperature group (n=18) having values of 32-36 °C. Effects of cybersickness on finger temperature depended on the basal level of this variable: in subjects from former group it raised by 3-4 °C, while in most subjects from the latter group it either did not change or transiently reduced by 1.5-2 °C. There was no correlation between the magnitude of changes in the finger temperature and nausea score at the end of simulated ride. Provocative visual stimulation caused prolongation of simple reaction time by 20-50 ms; this increase closely correlated with the subjective rating of nausea. Lastly, in subjects who experienced pronounced nausea, heart rate was elevated. We conclude that cybersickness is associated with changes in cutaneous thermoregulatory vascular tone; this further supports the idea of a tight link between motion sickness and thermoregulation. Cybersickness-induced prolongation of reaction time raises obvious concerns regarding the safety of this technology.

Combining sudomotor nerve impulse estimation with fMRI to investigate the central sympathetic response to nausea

The skin conductance (SC) signal is one of the most important non-invasive indirect measures of autonomic outflow. Several mathematical models have been proposed in the literature to characterize specific SC features. In this work, we present a method for the estimation of central control of sudomotor nerve impulse (SMI) function using SC. The method is based on a differential formulation decomposed into two first order differential equations. We validate our estimation framework by applying it on an experimental protocol where eleven motion sickness-prone subjects were exposed to a nauseogenic visual stimulus while SC and fMRI signals were recorded. Our results show an expected significant increase in the mean amplitude of SMI peaks during the highest reported nausea, as well as a decreasing trend during recovery, which was not evident for skin conductance level. Importantly, SMI/fMRI analysis found a negative association between SMI and fMRI signal in orbitofrontal, dorsolateral prefrontal, and posterior insula cortices, consistent with previous studies correlating brain fMRI and microneurographic signals.

Motion sickness, nausea and thermoregulation: The "toxic" hypothesis

Principal symptoms of motion sickness in humans include facial pallor, nausea and vomiting, and sweating. It is less known that motion sickness also affects thermoregulation, and the purpose of this review is to present and discuss existing data related to this subject. Hypothermia during seasickness was firstly noted nearly 150 years ago, but detailed studies of this phenomenon were conducted only during the last 2 decades. Motion sickness-induced hypothermia is philogenetically quite broadly expressed as besides humans, it has been reported in rats, musk shrews and mice. Evidence from human and animal experiments indicates that the physiological mechanisms responsible for the motion sickness-induced hypothermia include cutaneous vasodilation and sweating (leading to an increase of heat loss) and reduced thermogenesis. Together, these results suggest that motion sickness triggers highly coordinated physiological response aiming to reduce body temperature. Finally, we describe potential adaptive role of this response, and describe the benefits of using it as an objective measure of motion sickness-induced nausea.

Differential hypoglycaemic, anorectic, autonomic and emetic effects of the glucagon-like peptide receptor agonist, exendin-4, in the conscious telemetered ferret

Background

Rodents are incapable of emesis and consequently the emetic potential of glucagon-like peptide-1 receptor (GLP-1R) agonists in studies designed to assess a potential blood glucose lowering action of the compound was missed. Therefore, we investigated if the ferret, a carnivore with demonstrated translation capability in emesis research, would identify the emetic potential of the GLP-1R agonist, exendin-4, and any associated effects on gastric motor function, appetite and cardiovascular homeostasis.

Methods

The biological activity of the GLP-1R ligands was investigated in vivo using a glucose tolerance test in pentobarbitone-anesthetised ferrets and in vitro using organ bath studies. Radiotelemetry was used to investigate the effect of exendin-4 on gastric myoelectric activity (GMA) and cardiovascular function in conscious ferrets; behaviour was also simultaneously assessed. Western blot was used to characterize GLP-1R distribution in the gastrointestinal and brain tissues.

Results

In anesthetised ferrets, exendin-4 (30 nmol/kg, s.c.) reduced experimentally elevated blood glucose levels by 36.3%, whereas the GLP-1R antagonist, exendin (9–39) (300 nmol/kg, s.c.) antagonised the effect and increased AUC_0–120 by 31.0% when injected alone (P < 0.05). In animals with radiotelemetry devices, exendin-4 (100 nmol/kg, s.c.) induced emesis in 1/9 ferrets, but inhibited food intake and decreased heart rate variability (HRV) in all animals (P < 0.05). In the animals not exhibiting emesis, there was no effect on GMA, mean arterial blood pressure, heart rate, or core body temperature. In the ferret exhibiting emesis, there was a shift in the GMA towards bradygastria with a decrease in power, and a concomitant decrease in HRV. Western blot revealed GLP-1R throughout the gastrointestinal tract but exendin-4 (up to 300 nM) and exendin (9–39), failed to contract or relax isolated ferret gut tissues. GLP-1R were found in all major brain regions and the levels were comparable those in the vagus nerve.

Conclusions

Peripherally administered exendin-4 reduced blood glucose and inhibited feeding with a low emetic potential similar to that in humans (11% vs 12.8%). A disrupted GMA only occurred in the animal exhibiting emesis raising the possibility that disruption of the GMA may influence the probability of emesis occurring in response to treatment with GLP-1R agonists.

Brain Circuitry Supporting Multi-Organ Autonomic Outflow in Response to Nausea

While autonomic outflow is an important co-factor of nausea physiology, central control of this outflow is poorly understood. We evaluated sympathetic (skin conductance level) and cardiovagal (high-frequency heart rate variability) modulation, collected synchronously with functional MRI (fMRI) data during nauseogenic visual stimulation aimed to induce vection in susceptible individuals. Autonomic data guided analysis of neuroimaging data, using a stimulus-based (analysis windows set by visual stimulation protocol) and percept-based (windows set by subjects' ratings) approach. Increased sympathetic and decreased parasympathetic modulation was associated with robust and anti-correlated brain activity in response to nausea. Specifically, greater autonomic response was associated with reduced fMRI signal in brain regions such as the insula, suggesting an inhibitory relationship with premotor brainstem nuclei. Interestingly, some sympathetic/parasympathetic specificity was noted. Activity in default mode network and visual motion areas was anti-correlated with parasympathetic outflow at peak nausea. In contrast, lateral prefrontal cortical activity was anti-correlated with sympathetic outflow during recovery, soon after cessation of nauseogenic stimulation. These results suggest divergent central autonomic control for sympathetic and parasympathetic response to nausea. Autonomic outflow and the central autonomic network underlying ANS response to nausea may be an important determinant of overall nausea intensity and, ultimately, a potential therapeutic target.

Brain white matter microstructure is associated with susceptibility to motion-induced nausea

Nausea is associated with significant morbidity, and there is a wide range in the propensity of individuals to experience nausea. The neural basis of the heterogeneity in nausea susceptibility is poorly understood. Our previous functional magnetic resonance imaging (fMRI) study in healthy adults showed that a visual motion stimulus caused activation in the right MT+/V5 area, and that increased sensation of nausea due to this stimulus was associated with increased activation in the right anterior insula. For the current study, we hypothesized that individual differences in visual motion-induced nausea are due to microstructural differences in the inferior fronto-occipital fasciculus (IFOF), the white matter tract connecting the right visual motion processing area (MT+/V5) and right anterior insula. To test this hypothesis, we acquired diffusion tensor imaging data from 30 healthy adults who were subsequently dichotomized into high and low nausea susceptibility groups based on the Motion Sickness Susceptibility Scale. We quantified diffusion along the IFOF for each subject based on axial diffusivity (AD); radial diffusivity (RD), mean diffusivity (MD) and fractional anisotropy (FA), and evaluated between-group differences in these diffusion metrics. Subjects with high susceptibility to nausea rated significantly (P < 0.001) higher nausea intensity to visual motion stimuli and had significantly (P < 0.05) lower AD and MD along the right IFOF compared to subjects with low susceptibility to nausea. This result suggests that differences in white matter microstructure within tracts connecting visual motion and nausea-processing brain areas may contribute to nausea susceptibility or may have resulted from an increased history of nausea episodes.

A combined HRV-fMRI approach to assess cortical control of cardiovagal modulation by motion sickness

Nausea is a commonly occurring symptom typified by epigastric discomfort with the urge to vomit. To date, the brain circuitry underlying the autonomic nervous system response to nausea has not been fully understood. Functional MRI (fMRI), together with a point process adaptive recursive algorithm for computation of the high-frequency (HF) index of heart rate variability (HRV) was combined to evaluate the brain circuitry underlying autonomic nervous system response to nausea. Alone, the point process analysis revealed increasing sympathetic and decreasing parasympathetic response during nausea with significant increased heart rate (HR) and decreased HF. The combined HRV-fMRI analysis demonstrated that the fMRI signal in the medial prefrontal cortex (MPFC) and pregenual anterior cingulate cortex (pgACC), regions of higher cortical functions and emotion showed a negative correlation at the baseline and a positive correlation during nausea. Overall, our findings confirm a sympathovagal shift (toward sympathetic) during nausea, which was related to brain activity in regions associated with emotion and higher cognitive function.

The brain circuitry underlying the temporal evolution of nausea in humans

Nausea is a universal human experience. It evolves slowly over time, and brain mechanisms underlying this evolution are not well understood. Our functional magnetic resonance imaging (fMRI) approach evaluated brain activity contributing to and arising from increasing motion sickness. Subjects rated transitions to increasing nausea, produced by visually induced vection within the fMRI environment. We evaluated parametrically increasing brain activity 1) precipitating increasing nausea and 2) following transition to stronger nausea. All subjects demonstrated visual stimulus-associated activation (P < 0.01) in primary and extrastriate visual cortices. In subjects experiencing motion sickness, increasing phasic activity preceding nausea was found in amygdala, putamen, and dorsal pons/locus ceruleus. Increasing sustained response following increased nausea was found in a broader network including insular, anterior cingulate, orbitofrontal, somatosensory and prefrontal cortices. Moreover, sustained anterior insula activation to strong nausea was correlated with midcingulate activation (r = 0.87), suggesting a closer linkage between these specific regions within the brain circuitry subserving nausea perception. Thus, while phasic activation in fear conditioning and noradrenergic brainstem regions precipitates transition to strong nausea, sustained activation following this transition occurs in a broader interoceptive, limbic, somatosensory, and cognitive network, reflecting the multiple dimensions of this aversive commonly occurring symptom.