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IntroductionThe autonomic nervous system (ANS) modulates numerous processes, including metabolic control and visceral pain processing. Accumulating evidence purports that ANS function is disturbed in both inflammatory bowel disease and irritable bowel syndrome (IBS). Whilst the brain is a central hub for regulating autonomic function, the association between resting autonomic activity and subcortical morphology has not been comprehensively studied and thus we sought to address this knowledge gap.MethodIn twenty-seven healthy subjects (14 male and 13 female; mean age 30 years (range 22–53 years)), we quantified resting cardiac sympathetic index (CSI) and parasympathetic cardiac vagal tone (CVT) using a Neuroscope. Autonomic parameters were recorded as per international recommendations. In addition, high resolution structural magnetic resonance imaging scans were acquired using a GE Signa HDxt3.0 Tesla scanner. Subcortical shape differences, i.e. “deformation”, contingent on resting ANS activity were studied using FSL-FIRST, by means of positive and negative linear contrasts.ResultsCSI was significantly associated with outward deformation of the brainstem, right nucleus accumbens, right amygdala and bilateral pallidum (family-wise error (FWE) corrected p<0.05) (Figure 1, turquoise coloured areas of nuclei represent outward deformation associated with CSI). In contrast, CVT was significantly associated with inward deformation of the right amygdala and pallidum (FWE corrected p<0.05) (Figure 1, yellow coloured areas of nuclei represent inward deformation associated with CVT). Furthermore, bilateral putamen volume positively correlated with resting CVT (p<0.0003).[Figure]ConclusionOur study provides novel evidence that resting autonomic state is associated with differences in the shape and/or volume of subcortical nuclei. The Rome working group have highlighted that inter-individual differences are a key limiting factor in the neuroimaging of visceral pain, these data suggest that resting autonomic function reflects an additional important variable. Given that perturbations in autonomic function and brain morphological differences are well described in IBS, our findings suggest that future studies should control for resting autonomic tone as covariates.Disclosure of InterestJ. Ruffle: None Declared, S Coen: None Declared, V Giampietro: None Declared, S Williams: None Declared, A Farmer Conflict with: Medical Research Council Grant, Q Aziz Conflict with: Medical Research Council Grant

IntroductionVisceral pain is a complex experience, and is influenced by an array of physiological, psychological and anatomical factors. Previous research from our group has coalesced many of these factors, demonstrating that two major endophenotypic ‘pain clusters’ (PC) exist with the following features: Pain Cluster 1 (PC1), in comparison to Pain Cluster 2 (PC2), had higher neuroticism and anxiety scores, and the serotonin transporter-linked polymorphic region genotype (5-HTTLPR) short allele was over represented. PC1 had greater baseline sympathetic tone and serum cortisol, but during acute pain had a lower stimulus tolerance and increased parasympathetic tone. Meanwhile, PC2 had the converse profile at baseline and during pain. We hypothesised that these PCs could be predicted by whole brain functional connectivity during either rest or oesophageal pain, irrespective of any physiological, psychophysiological and genetic data.MethodWe used a previous dataset of 21 healthy subjects (10 male and 11 female; mean age 30 years), all of which were previously allocated to PC1 (n=9) or PC2 (n=12). All had additionally undergone fMRI with an event-related design of acute oesophageal pain and rest periods. Blood oxygen level dependant (BOLD) signal during rest and oesophageal balloon distention to pain tolerance threshold was extracted from a whole brain parcellation map of 346 single-voxel regions of interest (Figure 1a, single node example), which were cross-correlated to produce whole brain correlation matrices of 59 685 rvalues. Using complex decision trees, an aspect of the ‘classification-learner’ machine learning algorithm within Matlab, we investigated whether whole brain connectivity could accurately predict which cluster subjects were allocated to.[Figure]ResultsWhole brain functional connectivity during oesophageal pain accurately predicted subject PC with 85.7% accuracy: area under curve (AUC) 0.86; true positive rate (TPR) for PC1 and PC2 89% and 83% respectively; false negative rate (FNR) for PC1 and PC2 11% and 17% respectively (Figure 1b, receiver operating characteristic curve). However, PC were only predicted with 58% accuracy during rest: AUC 0.58; TPR for PC1 and PC2 44% and 75% respectively, FNR for PC1 and PC2 56% and 25%.ConclusionThese data suggest that endophenotypic PCs can be accurately predicted from whole brain functional connectivity during acute oesophageal pain, but not by resting connectivity. Future study should investigate for specific brain region connectivity and network differences between PCs to elucidate key differences.Disclosure of InterestJ. Ruffle: None Declared, S. Coen: None Declared, V. Giampietro: None Declared, S. Williams: None Declared, A. Farmer Conflict with: Medical Research Council Grant, Q. Aziz Conflict with: Medical Research Council Grant