Visceral region in the rat primary somatosensory cortex identified by vagal evoked potential

Primary somatosensory cortex organization for engineering artificial somatosensation

Somatosensory deficits from stroke, spinal cord injury, or other neurologic damage can lead to a significant degree of functional impairment. The primary (SI) and secondary (SII) somatosensory cortices encode information in a medial to lateral organization. SI is generally organized topographically, with more discrete cortical representations of specific body regions. SII regions corresponding to anatomical areas are less discrete and may represent a more functional rather than topographic organization. Human somatosensory research continues to map cortical areas of sensory processing with efforts primarily focused on hand and upper extremity information in SI. However, research into SII and other body regions is lacking. In this review, we synthesize the current state of knowledge regarding the cortical organization of human somatosensation and discuss potential applications for brain computer interface. In addition to accurate individualized mapping of cortical somatosensation, further research is required to uncover the neurophysiological mechanisms of how somatosensory information is encoded in the cortex.

Causality between inflammatory bowel disease and the cerebral cortex: insights from Mendelian randomization and integrated bioinformatics analysis

Background

Inflammatory bowel disease (IBD), which includes ulcerative colitis (UC) and Crohn's disease (CD), is a chronic, progressive, and recurrent intestinal condition that poses a significant global health burden. The high prevalence of neuropsychiatric comorbidities in IBD necessitates the development of targeted management strategies.

Methods

Leveraging genetic data from genome-wide association studies and Immunochip genotype analyses of nearly 150,000 individuals, we conducted a two-sample Mendelian randomization study to elucidate the driving force of IBD, UC, and CD on cortical reshaping. Genetic variants mediating the causality were collected to disclose the biological pathways linking intestinal inflammation to brain dysfunction.

Results

Here, 115, 69, and 98 instrumental variables genetically predicted IBD, UC, and CD. We found that CD significantly decreased the surface area of the temporal pole gyrus (β = -0.946 mm2, P = 0.005, false discovery rate-P = 0.085). Additionally, we identified suggestive variations in cortical surface area and thickness induced by exposure across eight functional gyri. The top 10 variant-matched genes were STAT3, FOS, NFKB1, JAK2, STAT4, TYK2, SMAD3, IL12B, MYC, and CCL2, which are interconnected in the interaction network and play a role in inflammatory and immune processes.

Conclusion

We explore the causality between intestinal inflammation and altered cortical morphology. It is likely that neuroinflammation-induced damage, impaired neurological function, and persistent nociceptive input lead to morphological changes in the cerebral cortex, which may trigger neuropsychiatric disorders.

Connectomic profiling and Vagus nerve stimulation Outcomes Study (CONNECTiVOS): a prospective observational protocol to identify biomarkers of seizure response in children and youth

INTRODUCTION

Vagus nerve stimulation (VNS) is a neuromodulation therapy that can reduce the seizure burden of children with medically intractable epilepsy. Despite the widespread use of VNS to treat epilepsy, there are currently no means to preoperatively identify patients who will benefit from treatment. The objective of the present study is to determine clinical and neural network-based correlates of treatment outcome to better identify candidates for VNS therapy.

METHODS AND ANALYSIS

In this multi-institutional North American study, children undergoing VNS and their caregivers will be prospectively recruited. All patients will have documentation of clinical history, physical and neurological examination and video electroencephalography as part of the standard clinical workup for VNS. Neuroimaging data including resting-state functional MRI, diffusion-tensor imaging and magnetoencephalography will be collected before surgery. MR-based measures will also be repeated 12 months after implantation. Outcomes of VNS, including seizure control and health-related quality of life of both patient and primary caregiver, will be prospectively measured up to 2 years postoperatively. All data will be collected electronically using Research Electronic Data Capture.

ETHICS AND DISSEMINATION

This study was approved by the Hospital for Sick Children Research Ethics Board (REB number 1000061744). All participants, or substitute decision-makers, will provide informed consent prior to be enrolled in the study. Institutional Research Ethics Board approval will be obtained from each additional participating site prior to inclusion. This study is funded through a Canadian Institutes of Health Research grant (PJT-159561) and an investigator-initiated funding grant from LivaNova USA (Houston, TX; FF01803B IIR).

The Influence of Stomach Back-Shu and Front-Mu Points on Insular Functional Connectivity in Functional Dyspepsia Rat Models

Functional Dyspepsia (FD) is a common functional gastrointestinal disease, which can reduce the quality of life in patients. Prior research has indicated that insula is closely related to FD and that acupuncture can regulate the functional connectivity (FC) of FD. Therefore, we hypothesized that acupuncture on FD was effected through the insular pathway. To test our hypothesis, we performed electroacupuncture (EA) on FD rat models and then examined the FC between insula and other brain regions through resting-state functional magnetic resonance imaging (rs-fMRI). Seven-day-old male infant Sprague-Dawley (SD) rats were randomly divided into control group, FD model group, and FD acupuncture group, with twelve rats per group (n = 36). Upon establishing successful models, the FD acupuncture group was subjected to EA intervention using Stomach back-shu (BL-21) and front-mu (RN-12) points for ten consecutive days for durations of 20 minutes each day. After intervention, each group was subject to rs-fMRI. The digital image data obtained were analyzed using FC analysis methods. Subsequently, gastric ligation was performed to measure gastric emptying rates. Before EA intervention, the FD model group exhibited decreased functional connections between the insula and a number of brain regions. After EA intervention, FD acupuncture group exhibited increasing FC between insula and regions when compared to the FD model group, such as the primary somatosensory cortex (S1), hippocampal CA3 (CA3), polymorphic layer of dentate gyrus (PoDG), caudate putamen (CPu), and oral pontine reticular nuclei (PnO) (P < 0.05); decreasing FC was also exhibited between insula and regions such as the bilateral primary and secondary motor cortexes (M1/2), paraventricular hypothalamic nucleus (PVA), and limbic cortex (LC). These findings indicate that the effective treatment of FD using EA may be through regulating the abnormal FC between insula and several brain regions, in particular CA3, PoDG, and PVA.

Cortical neurochemical signaling of gustatory stimuli and their visceral consequences during the acquisition and consolidation of taste aversion memory

The insular cortex (IC) has a crucial role in taste recognition memory, including conditioned taste aversion (CTA). CTA is a learning paradigm in which a novel taste stimulus (CS) is associated with gastric malaise (US), inducing aversion to the CS in future encounters. The role of the IC in CTA memory formation has been extensively studied. However, the functional significance of neurotransmitter release during the presentation of taste stimuli and gastric malaise-inducing agents remains unclear. Using microdialysis in free-moving animals, we evaluated simultaneous changes in glutamate, norepinephrine and dopamine release in response to the presentation of an innate appetitive or aversive gustatory novel stimulus, as well as after i.p. administration of isotonic or hypertonic gastric malaise-inducing solutions. Our results demonstrate that the presentation of novel stimuli, regardless of their innate valence, induces an elevation of norepinephrine and dopamine. Administration of a gastric malaise inducing agent (LiCl) promotes an elevation of glutamate regardless of its concentration. In comparison, norepinephrine release is related to the LiCl concentration and its equimolar NaCl control. Additionally, we evaluated their functional role on short and long-term taste aversion memory. Results indicate that the blockade of noradrenergic β1,2 receptors in the IC spares CTA acquisition and memory consolidation. In contrast, blockade of dopamine D1/D5 receptors impaired CTA consolidation, whereas the NMDA receptor blockade impedes both acquisition and consolidation of CTA. These results suggest that dopaminergic and noradrenergic release are related to the salience of conditioned taste stimuli. However, only cortical D1/D5 dopaminergic activity, but not the noradrenergic β1,2 activity, is involved in the acquisition and consolidation of taste memory formation. Additionally, glutamatergic activity signals visceral distress caused by LiCl administration and activates NMDA receptors necessary for the acquisition and consolidation of long-lasting taste aversion memory.

Mini Review: Central Organization of Airway Afferent Nerve Circuits

Airway afferents monitor the local chemical and physical micro-environments in the airway wall and lungs and send this information centrally to regulate neural circuits involved in setting autonomic tone, evoking reflex and volitional respiratory motor outflows, encoding perceivable sensations and contributing to higher order cognitive processing. In this mini-review we present a current overview of the central wiring of airway afferent circuits in the brainstem and brain, highlighting recent discoveries that augment our understanding of airway sensory processing. We additionally explore how advances in describing the molecular diversity of airway afferents may influence future research efforts aimed at defining central mesoscale connectivity of airway afferent pathways. A refined understanding of how functionally distinct airway afferent pathways are organized in the brain will provide deeper insight into the physiology of airway afferent-evoked responses and may foster opportunities for targeted modulation of specific pathways involved in disease.

Somatosensory evoked fields predict response to vagus nerve stimulation

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There is a need to preoperatively identify children who will respond to VNS.

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There is similarity between the afferent vagus and median nerve projections to S1.

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Median nerve somatosensory evoked fields identify those who will respond to VNS.

There is an unmet need to develop robust predictive algorithms to preoperatively identify pediatric epilepsy patients who will respond to vagus nerve stimulation (VNS). Given the similarity in the neural circuitry between vagus and median nerve afferent projections to the primary somatosensory cortex, the current study hypothesized that median nerve somatosensory evoked field(s) (SEFs) could be used to predict seizure response to VNS. Retrospective data from forty-eight pediatric patients who underwent VNS at two different institutions were used in this study. Thirty-six patients (“Discovery Cohort”) underwent preoperative electrical median nerve stimulation during magnetoencephalography (MEG) recordings and 12 patients (“Validation Cohort”) underwent preoperative pneumatic stimulation during MEG. SEFs and their spatial deviation, waveform amplitude and latency, and event-related connectivity were calculated for all patients. A support vector machine (SVM) classifier was trained on the Discovery Cohort to differentiate responders from non-responders based on these input features and tested on the Validation Cohort by comparing the model-predicted response to VNS to the known response. We found that responders to VNS had significantly more widespread SEF localization and greater functional connectivity within limbic and sensorimotor networks in response to median nerve stimulation. No difference in SEF amplitude or latencies was observed between the two cohorts. The SVM classifier demonstrated 88.9% accuracy (0.93 area under the receiver operator characteristics curve) on cross-validation, which decreased to 67% in the Validation cohort. By leveraging overlapping neural circuitry, we found that median nerve SEF characteristics and functional connectivity could identify responders to VNS.

A Single Intraperitoneal Injection of Endotoxin Changes Glial Cells in Rats as Revealed by Positron Emission Tomography Using [11C]PK11195

Purpose

Intracranial administration of lipopolysaccharide (LPS) is known to elicit a rapid innate immune response, activate glial cells in the brain, and induce depression-like behavior. However, no study has focused on the changes in glial cells induced by intraperitoneal injection of LPS in vivo.

Methods

Ten adult male Fischer F344 rats underwent [¹¹C]PK11195 PET before and 2 days after intraperitoneal injection of LPS to evaluate the changes in glial cells. The difference in standardized uptake values (SUV) of [¹¹C]PK11195 between before and after injection was determined.

Results

There was a cluster of brain regions that showed significant reductions in SUV. This cluster included the bilateral striata and bilateral frontal regions, especially the somatosensory areas.

Conclusions

Changes in activity of glial cells induced by the intraperitoneal injection of LPS were detected in vivo by [¹¹C]PK11195 PET. Intraperitoneal injection of LPS is known to induce depression, and further studies with [¹¹C]PK11195 PET would clarify the relationships between neuroinflammation and depression.

Vagal Afferent Innervation of the Airways in Health and Disease

Vagal sensory neurons constitute the major afferent supply to the airways and lungs. Subsets of afferents are defined by their embryological origin, molecular profile, neurochemistry, functionality, and anatomical organization, and collectively these nerves are essential for the regulation of respiratory physiology and pulmonary defense through local responses and centrally mediated neural pathways. Mechanical and chemical activation of airway afferents depends on a myriad of ionic and receptor-mediated signaling, much of which has yet to be fully explored. Alterations in the sensitivity and neurochemical phenotype of vagal afferent nerves and/or the neural pathways that they innervate occur in a wide variety of pulmonary diseases, and as such, understanding the mechanisms of vagal sensory function and dysfunction may reveal novel therapeutic targets. In this comprehensive review we discuss historical and state-of-the-art concepts in airway sensory neurobiology and explore mechanisms underlying how vagal sensory pathways become dysfunctional in pathological conditions.

Phase-amplitude coupling at the organism level: The amplitude of spontaneous alpha rhythm fluctuations varies with the phase of the infra-slow gastric basal rhythm

A fundamental feature of the temporal organization of neural activity is phase-amplitude coupling between brain rhythms at different frequencies, where the amplitude of a higher frequency varies according to the phase of a lower frequency. Here, we show that this rule extends to brain-organ interactions. We measured both the infra-slow (~0.05Hz) rhythm intrinsically generated by the stomach - the gastric basal rhythm - using electrogastrography, and spontaneous brain dynamics with magnetoencephalography during resting-state with eyes open. We found significant phase-amplitude coupling between the infra-slow gastric phase and the amplitude of the cortical alpha rhythm (10-11Hz), with gastric phase accounting for 8% of the variance of alpha rhythm amplitude fluctuations. Gastric-alpha coupling was localized to the right anterior insula, and bilaterally to occipito-parietal regions. Transfer entropy, a measure of directionality of information transfer, indicates that gastric-alpha coupling is due to an ascending influence from the stomach to both the right anterior insula and occipito-parietal regions. Our results show that phase-amplitude coupling so far only observed within the brain extends to brain-viscera interactions. They further reveal that the temporal structure of spontaneous brain activity depends not only on neuron and network properties endogenous to the brain, but also on the slow electrical rhythm generated by the stomach.

The stomach-brain axis

The stomach has distinct functions in relation to the ingestion and handling of solids and liquids. These functions include storage of the food before it is gradually emptied into the duodenum, mechanical crushing of larger food particles to increase the surface area, secretion of an acidic enzyme rich gastric juice and mixing the ingested food with the gastric juice. In addition, the stomach 'senses' the composition of the gastric content and this information is passed via the vagal nerve to the lateral hypothalamus and the limbic system, most likely as palatability signals that influence eating behaviour. Other sensory qualities related to the stimulation of gastric tension receptors are satiety and fullness. Receptors that respond to macronutrient content or gastric wall tension influence appetite and meal related hormone responses. The ingestion of food - in contrast to an infusion of nutrients into the stomach - has distinct effects on the activation of specific brain regions. Brain areas such as thalamus, amygdala, putamen and praecuneus are activated by the ingestion of food. Gastric nutrient infusion evokes greater activation in the hippocampus and anterior cingulate. The brain integrates these interrelated neural and hormonal signals arising from the stomach as well as visual, olfactory and anticipatory stimuli that ultimately influence eating and other behavioural patterns. Furthermore, there is now good evidence from experimental studies that gastric afferents influence mood, and animal studies point towards the possibility that gastric dysfunction may be a risk factor for mood disorders such as anxiety and depression. The stomach is also not only colonised by Helicobacter pylori but a large array of bacteria. While there is sufficient evidence to suggest that H. pylori may alter caloric intake and mood, the role of other gastric microbiome for the brain function is unknown. To address this appropriate targeted gastric microbiome studies would be required instead of widely utilised opportunistic stool microbiome studies. In summary, it is now well established that there are important links between the brain and the stomach that have significant effects on gastric function. However, the stomach also influences the brain. Disturbances in the crosstalk between the stomach and the brain may manifest as functional GI disorders while disturbances in the stomach-brain communication may also result in an altered regulation of satiety and as a consequence may affect eating behaviour and mood. These observations may enable the identification of novel therapies targeted at the gastroduodenum that positively alter brain function and treat or prevent conditions such as obesity or functional gastrointestinal disorders.

Anatomical and electrophysiological mechanisms for asymmetrical excitatory propagation in the rat insular cortex: in vivo optical imaging and whole-cell patch-clamp studies

The insular cortex (IC) integrates limbic information from the amygdala and hypothalamic nucleus to multimodal sensory inputs, including visceral, gustatory, and somatosensory information. However, the functional framework of excitation in the IC is still unknown. We performed optical imaging and single pyramidal neuronal staining using a whole-cell patch-clamp technique in urethane-anesthetized rats to elucidate the precise anatomical and physiological features of IC pyramidal neurons, which regulate cortical information processing via their horizontal connections. Optical imaging revealed that electrical stimulation of the granular (GI) or dysgranular (DI) IC elicited characteristic excitatory propagations along the rostrocaudal axis parallel to the rhinal fissure, with a preference toward the rostral direction. Spatial patterns of the dendrites and axons of layer II/III pyramidal cells in the DI/GI support these functional features of excitation; for example, rostrocaudal axonal arbors tend to extend with a rostral directional preference. The mean length of the axons from the soma to the farthest site rostrally was ∼50% longer than that of the caudal length. Pyramidal cells in the DI/GI exhibited spontaneous membrane oscillation in the UP and DOWN states. Similarly to the evoked signals obtained by optical imaging, repetitive electrical stimulation of the caudal IC ∼1 mm away from the recorded cells (five pulses at 50 Hz) induced the summation of evoked excitatory postsynaptic potentials during the DOWN state and profound inhibitory postsynaptic potentials during the UP state. Clarification of the excitation feature with its cellular basis provides new clues about the functional mechanisms of the asymmetric propagation of neural activities in the IC.

Cortical visual areas process intestinal information during slow-wave sleep

BACKGROUND

Previously we have shown that, during sleep, electrical and magnetic stimulation of areas of the stomach and small intestine evoked neuronal and EEG responses in various cortical areas. In this study we wanted to correlate natural myoelectrical activity of the duodenum with cortical neuronal activity, and to investigate whether there is a causal link between them during periods of slow-wave sleep.

METHODS

We have recorded the myoelectrical activity from the wall of the duodenum and activity of single neurons from three cortical visual areas in naturally sleeping cats and investigated causal interrelationship between these structures during slow-wave sleep.

KEY RESULTS

About 30% of the cortical neurons studied changed their firing rate dependent on the phases of the peristaltic cycle and demonstrated selectivity to particular pattern of duodenal myoelectrical activity during slow-wave sleep. This interrelationship was never seen when awake.

CONCLUSIONS & INFERENCES

This observation supports the hypothesis that, during sleep, the cerebral cortex switches from processing of exteroceptive and proprioceptive information to processing of interoceptive information.

Autonomic neural control of the airways

The airways and lungs are innervated by both sympathetic and parasympathetic nerves. Cholinergic parasympathetic innervation is well conserved in the airways while the distribution of noncholinergic parasympathetic and adrenergic sympathetic nerves varies considerably amongst species. Autonomic nerve function is regulated primarily through reflexes initiated upon bronchopulmonary vagal afferent nerves. Central regulation of autonomic tone is poorly described but some key elements have been defined.

Anterograde neuronal circuit tracing using a genetically modified herpes simplex virus expressing EGFP

Insights into the anatomical organization of complex neural circuits provide important information about function, and thus tools that facilitate neuroanatomical studies have proved invaluable in neuroscience. Advances in molecular cloning have allowed the production of novel recombinant neuroinvasive viruses for use in transynaptic neural tracing studies. However, the vast majority of these viruses have motility in the retrograde direction only, therefore limiting their use to studies of synaptic input circuitry. Here we describe the construction of an EGFP reporting herpes simplex virus, strain H129, which preferentially moves along synaptically connected neurons in the anterograde direction. In vitro and in vivo characterization studies confirm that the HSV-1 H129-EGFP retains comparable replication and neuroinvasiveness as the wildtype H129 virus. As a proof of principle we confirm anterograde movement of the H129-EGFP along polysynaptic pathways by inoculating the upper airways and tracking time-dependent EGFP expression in previously described ascending sensory pathways. These data confirm a genomic locus for recombining HSV-1 H129 such that normal viral function and replication is maintained. Novel viral recombinants such as HSV-1 H129-EGFP will be useful tools for delineating the central organization of peripheral sensory pathways as well as the synaptic outputs from central neuronal populations.

Transneuronal tracing of airways-related sensory circuitry using herpes simplex virus 1, strain H129

Sensory input from the airways to suprapontine brain regions contributes to respiratory sensations and the regulation of respiratory function. However, relatively little is known about the central organization of this higher brain circuitry. We exploited the properties of the H129 strain of herpes simplex virus 1 (HSV-1) to perform anterograde transneuronal tracing of the central projections of airway afferent nerve pathways. The extrathoracic trachea in Sprague-Dawley rats was inoculated with HSV-1 H129, and tissues along the neuraxis were processed for HSV-1 immunoreactivity. H129 infection appeared in the vagal sensory ganglia within 24 h and the number of infected cells peaked at 72 h. Brainstem nuclei, including the nucleus of the solitary tract and trigeminal sensory nuclei were infected within 48 h, and within 96 h infected cells were evident within the pons (lateral and medial parabrachial nuclei), thalamus (ventral posteromedial, ventral posterolateral, submedius, and reticular nuclei), hypothalamus (paraventricular and lateral nuclei), subthalamus (zona incerta), and amygdala (central and anterior amygdala area). At later times H129 was detected in cortical forebrain regions including the insular, orbital, cingulate, and somatosensory cortices. Vagotomy significantly reduced the number of infected cells within vagal sensory nuclei in the brainstem, confirming the main pathway of viral transport is through the vagus nerves. Sympathetic postganglionic neurons in the stellate and superior cervical ganglia were infected by 72 h, however, there was no evidence for retrograde transynaptic movement of the virus in sympathetic pathways in the central nervous system (CNS). These data demonstrate the organization of key structures within the CNS that receive afferent projections from the extrathoracic airways that likely play a role in the perception of airway sensations.

Disrupting vagal feedback affects birdsong motor control

Coordination of different motor systems for sound production involves the use of feedback mechanisms. Song production in oscines is a well-established animal model for studying learned vocal behavior. Whereas the online use of auditory feedback has been studied in the songbird model, very little is known about the role of other feedback mechanisms. Auditory feedback is required for the maintenance of stereotyped adult song. In addition, the use of somatosensory feedback to maintain pressure during song has been demonstrated with experimentally induced fluctuations in air sac pressure. Feedback information mediating this response is thought to be routed to the central nervous system via afferent fibers of the vagus nerve. Here, we tested the effects of unilateral vagotomy on the peripheral motor patterns of song production and the acoustic features. Unilateral vagotomy caused a variety of disruptions and alterations to the respiratory pattern of song, some of which affected the acoustic structure of vocalizations. These changes were most pronounced a few days after nerve resection and varied between individuals. In the most extreme cases, the motor gestures of respiration were so severely disrupted that individual song syllables or the song motif were atypically terminated. Acoustic changes also suggest altered use of the two sound generators and upper vocal tract filtering, indicating that the disruption of vagal feedback caused changes to the motor program of all motor systems involved in song production and modification. This evidence for the use of vagal feedback by the song system with disruption of song during the first days after nerve cut provides a contrast to the longer-term effects of auditory feedback disruption. It suggests a significant role for somatosensory feedback that differs from that of auditory feedback.

Far field potentials from brain stem after transcutaneous vagus nerve stimulation: optimization of stimulation and recording parameters

The method of vagus somatosensory evoked potentials (VSEP) was introduced to easily measure the activity of vagus brain stem nuclei. In Alzheimer's disease, this measure was characterized by longer latencies as compared to controls while amplitudes did not show statistical significant differences at frontal and central recording sites. Therefore, the influence of stimulation and recording parameters on amplitudes of VSEP were systematically examined. In 20 healthy participants, VSEP measurement was done by electrical stimulation of the cutaneous representation of the vagus nerve in the external auditory channel and recording of VSEP over the scalp. The optimum stimulation intensity is 8 mA without perception of pain. There is no effect of stimulation side or gender. Maximum VSEP amplitudes are detected at bipolar recordings comprising the electrode T4 without statistically significant differences of latencies, wave shape and polarity. Thus, recordings of future examinations should be performed at 8 mA including this temporal electrode position. The reason for focussing on brain stem evoked potentials is that recent work has accumulated evidence for this area being involved in early phases of neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. Improved methodological knowledge may facilitate the assessment of this non-invasive and cost-effective method in the early diagnosis of neurodegenerative disorders.

Is it possible to generate cerebral evoked potentials with a mechanical stimulus from the duodenum in rats?

The study aim was to develop a model to generate cerebral evoked potentials (CEPs) by mechanical distention of the duodenum in rats. Twenty Sprague-Dawley rats were anaesthetized and the EEG recorded from the left and right somatosensory cortices (S1L, S1R). A balloon catheter was implanted into the duodenum. A pneumatic device, triggered by data acquisition software, inflated the balloon for 200 ms every 3s to deliver a repeatable noxious stimulus. EEG was recorded for 100 ms before and 500 ms after onset of inflation and the response to 512 stimuli averaged to generate a CEP. Two CEPs were generated in each animal and data summed to calculate a single CEP for each channel. Data were excluded when the signal to noise ratio was < 2, therefore data are presented from 11 animals. A repeatable CEP was identified in waveforms recorded from S1L. The mean (S.D.) CEP comprised a triphasic waveform (P1, N1, P2) with latencies of 246.0 (24.7), 289.3 (12.8) and 321.5 (13.2)ms, respectively. We are the first group to have generated and characterized a CEP following mechanical stimulation of the duodenum. This model can be applied to further elucidate the mechanisms leading to visceral pain perception.

Gastric fundic distension activates fronto-limbic structures but not primary somatosensory cortex: a functional magnetic resonance imaging study

INTRODUCTION

The brain representation of visceral stimulation bears important similarities to that of somatic stimulation. However, the role of the primary (S1) and secondary (S2) somatosensory cortices in mediating gastric sensation is uncertain.

MATERIALS AND METHODS

Eighteen healthy, right-handed volunteers (age 32 years+/-6.5 years; 14 men) underwent dynamic assessment of the relationship between sensation and fundic barostat distending pressure and volume, and then brain functional magnetic resonance imaging (fMRI) during noxious fundic distension. Cytoarchitectonic probability maps were used to examine in detail the null hypothesis that fundic distension did not produce significant activation of S1 or S2.

RESULTS

Distending volume explained 74% of the variance in gastric sensation, compared to 64% with distending pressure. Incorporating distending volume into the regressor function for our fMRI analyses, we found that noxious fundic distension activated a widespread network of brain regions, including the pontine brainstem, thalami, cerebellum, insular cortex bilaterally, anterior and posterior cingulate cortex, right frontal lobe, and inferior parietal lobules. In detailed analyses, we found no evidence of activation of S1, but did find activation in one region of S2.

DISCUSSION

Our findings suggest that an extensive, predominantly fronto-limbic network of brain regions, including the insular cortex, mediates perception of noxious gastric fundic distension in healthy humans, without significant participation by the primary somatosensory cortex. This and other recent studies lay the groundwork for investigations comparing brain processing of visceral stimuli between healthy volunteers and patients with functional dyspepsia.

"Pusher syndrome" following cortical lesions that spare the thalamus

Stroke patients with "pusher syndrome" show severe misperception of their own upright body orientation although visual-vestibular processing is almost intact. This dissociation argues for a second graviceptive system in humans for the perception of body orientation. Recent studies revealed that the posterior thalamus is an important part of this system. The present investigation aimed to study the cortical representation of this system beyond the thalamus. We evaluated 45 acute patients with and without contraversive pushing following left-or right-sided cortical lesions sparing the thalamus. In both hemispheres, the simple lesion overlap associated with contraversive pushing typically centered on the insular cortex and parts of the postcentral gyrus. The comparison between pusher patients and controls who were matched with respect to age, lesion size, and the frequency of spatial neglect, aphasia and visual field defects revealed only very small regions that were specific for the pusher patients with cortical damage sparing the thalamus. Obviously, the cortical structures representing our control of upright body orientation are in close anatomical proximity to those areas that induce aphasia in the left hemisphere and spatial neglect in the right hemisphere when lesioned. We conclude that in addition to the subcortical area previously identified in the posterior thalamus, parts of the insula and postcentral gyrus appear to contribute at cortical level to the processing of the afferent signals mediating the graviceptive information about upright body orientation.

Vagal-Evoked Activity in the Parafascicular Nucleus of the Primate Thalamus

The physiological effects of ascending vagal afferent activity in the primate forebrain have not been established, and because vagus nerve stimulation (VNS) is useful clinically for treatment of epilepsy and depression, these actions need to be identified. We used a roving microelectrode to record vagal-evoked potentials in the thalamus of the macaque monkey. In addition to the anticipated activation in the gustatory/visceral thalamic relay nucleus, we found an unexpectedly larger and earlier response focus with multi-unit discharges in the adjacent parafascicular nucleus. These data reveal a potent vagal input to this intralaminar nucleus, which is normally considered to be involved in motor control. This finding indicates that a role for this vagal activation site in the anti-epileptic effects of VNS needs to be considered.

Brain processing of esophageal sensation in health and disease

This case study demonstrates that patients with NCCP can be subclassified on the basis of sensory responsiveness and neurophysiologic profiles. This approach identifies specific abnormalities within the CNS processing of esophageal sensation in individual patients, allowing us to objectively differentiate those with sensitized esophageal afferents from those that are hypervigilant to esophageal sensations. The importance of this approach is to underline that NCCP comprises a heterogeneous group of patients. and only when we have defined the phenotype of this condition and identified groups of patients with specific CNS abnormalities will it be possible to perform clinical studies aimed at answering specific hypotheses. The development of a comprehensive pathophysiologic model that identifies the specific causes of symptoms in patients with esophageal hypersensitivity will allow the future management strategies of these patients to be targeted more specifically and efficiently. This will have great benefits to patients'well-being and health care use.

Organization of somatosensory cortex in the laboratory rat (Rattus norvegicus): Evidence for two lateral areas joined at the representation of the teeth

Lateral somatosensory areas have not been explored in detail in rats, and theories on the organization of this region are based largely on anatomical tracing experiments. We investigated the topography of this region by using microelectrode recordings, which were related to flattened cortical sections processed for cytochrome oxidase (CO). Two lateral somatosensory areas were identified, each containing a complete representation of the body. A larger, more medial representation formed a mirror image of S1 along the rostrocaudal axis of the head region corresponding to the previously identified secondary somatosensory area (S2). A smaller, more lateral representation formed a mirror image of S2 along the rostrocaudal axis of the forelimb and hindlimb regions and likely corresponds to the parietal ventral area (PV) identified in other mammals. We also investigated the representation of the dentition and identified regions of cortex responsive to tooth stimulation. The lower incisor representation was rostral to the lower lip region of S1, and the upper incisor representation was lateral to the buccal pad region of S1. The upper and lower incisors flanked the tongue representation. An additional large region of far lateral cortex responded to both incisors. Finally, five CO-dense modules were consistently identified rostral and lateral to the S1 face representation, which we refer to as OM1, OM2, OM3, FM, and HM. These modules closely correspond to the physiologically identified areas representing the lower incisor (OM1) and tongue (OM2) regions of S1 and the mixed tooth (OM3), forelimb (FM1), and hindlimb (HM) representations of S2 and PV.

Vagal input to lateral area 3a in cat cortex

Penfield's sensory homunculus included visceral organs at its lateral extreme, and vagal input was recently identified lateral to the intraoral representation in primary somatosensory cortex (S1) of rats. We tested whether vagal input is similarly located in cats where area 3b (equivalent to S1) is clearly distinguishable from adjacent regions. Field potentials were recorded from the intact dura over the left hemisphere using electrical stimulation of the left or right cervical vagus nerve in seven cats. A surface positive-negative potential was evoked from either side in the lateral part of the sigmoid gyrus. Finer mapping made at the pial surface with a microelectrode identified a focal site anteromedial to the anterior tip of the coronal sulcus. Depth recordings demonstrated polarity reversals and multi-unit vagal responses, indicating that the potentials were generated by an afferent activation focus in the middle layers of the cortex. The S1 mechanoreceptive representation was localized by mapping multi-unit somatosensory receptive fields in the middle cortical layers near the coronal sulcus. The vagal-evoked potential site was distinctly anterior to the intraoral S1 representation and adjacent to the masseteric-nerve-evoked potential focus. Lesions made at the focal site revealed that this site is cytoarchitectonically located in area 3a not area 3b. Thus vagal input to the sensorimotor cortex in cats resembles deep rather than cutaneous somatic input, similar to the localization of nociceptive-specific input to area 3a in monkeys. The possibilities are considered that this vagal input is involved in motor control and in the sensory experience of visceral afferent activity.

Differentiation of visceral and cutaneous pain in the human brain

The widespread convergence of information from visceral, cutaneous, and muscle tissues onto CNS neurons invites the question of how to identify pain as being from the viscera. Despite referral of visceral pain to cutaneous areas, individuals regularly distinguish cutaneous and visceral pain and commonly have contrasting behavioral reactions to each. Our study addresses this dilemma by directly comparing human neural processing of intensity-equated visceral and cutaneous pain. Seven subjects underwent fMRI scanning during visceral and cutaneous pain produced by balloon distention of the distal esophagus and contact heat on the midline chest. Stimulus intensities producing nonpainful and painful sensations, interleaved with rest periods, were presented in each functional run. Analyses compared painful to nonpainful conditions. A similar neural network, including secondary somatosensory and parietal cortices, thalamus, basal ganglia, and cerebellum, was activated by visceral and cutaneous painful stimuli. However, cutaneous pain evoked higher activation bilaterally in the anterior insular cortex. Further, cutaneous but not esophageal pain activated ventrolateral prefrontal cortex, despite higher affective scores for visceral pain. Visceral but not cutaneous pain activated bilateral inferior primary somatosensory cortex, bilateral primary motor cortex, and a more anterior locus within anterior cingulate cortex. Our results reveal a common cortical network subserving cutaneous and visceral pain that could underlie similarities in the pain experience. However, we also observed differential activation patterns within insular, primary somatosensory, motor, and prefrontal cortices that may account for the ability to distinguish visceral and cutaneous pain as well as the differential emotional, autonomic and motor responses associated with these different sensations.