Probing the interoceptive network by listening to heartbeats: an fMRI study

Exposure to cues of homeostatic relevance (i.e. heartbeats) is supposed to increase the allocation of attentional resources towards the cue, due to its importance for self-regulatory, interoceptive processes. This functional magnetic resonance imaging (fMRI) study aimed at determining whether listening to heartbeats is accompanied by activation in brain areas associated with interoception, particularly the insular cortex. Brain activity was measured with fMRI during cue-exposure in 36 subjects while listening to heartbeats vs. sinus tones. Autonomic markers (skin conductance) and subjective measures of state and trait anxiety were assessed. Stimulation with heartbeat sounds triggered activation in brain areas commonly associated with the processing of interoceptive information, including bilateral insular cortices, the inferior frontal operculum, and the middle frontal gyrus. A psychophysiological interaction analysis indicated a functional connectivity between the middle frontal gyrus (seed region) and bilateral insular cortices, the left amygdala and the supplementary motor area. The magnitude of neural activation in the right anterior insular cortex was positively associated with autonomic arousal. The present findings indicate that listening to heartbeats induced activity in areas of the interoception network as well as changes in psychophysiological arousal and subjective emotional experience. As this approach constitutes a promising method for studying interoception in the fMRI environment, a clinical application in anxiety prone populations should be addressed by future studies

Behavioural data, illustrated separately for each experimental condition (H50, H100, T50, T100).

<p>Upper half: Subjective ratings on the dimensions arousal, valence, anxiety, and authenticity. Higher values indicate higher arousal, but positive valence. Lower half: Skin conductance data (range-corrected values). Error bars indicate the standard error of mean (SEM). #NS.SCR: mean number of non-stimulus specific skin conductance reactions; AMP.NS.SCR: mean amplitude of non-stimulus specific skin conductance reactions. * p < 0.05. ** p < 0.01</p

PPI results for the contrast heart > tone; seed region: right insula (x = 39, y = 15, z = 3).

<p><i>Note</i>. Significance threshold: p < 0.01 (uncorrected); minimum cluster size: 10 voxels.</p><p>PPI results for the contrast heart > tone; seed region: right insula (x = 39, y = 15, z = 3).</p

Behavioural data, illustrated separately for each experimental condition (H50, H100, T50, T100).

<p>Upper half: Subjective ratings on the dimensions arousal, valence, anxiety, and authenticity. Higher values indicate higher arousal, but positive valence. Lower half: Skin conductance data (range-corrected values). Error bars indicate the standard error of mean (SEM). #NS.SCR: mean number of non-stimulus specific skin conductance reactions; AMP.NS.SCR: mean amplitude of non-stimulus specific skin conductance reactions. * p < 0.05. ** p < 0.01</p

Demographic characteristics and questionnaire scores of the sample.

<p><i>Note</i>. Means and Standard Deviations are reported, except for the variables “Female gender” and “Smoking”. ASI = Anxiety Sensitivity Index; BDI II = Beck Depression Inventory II.</p><p>Means (SD) except where noted.</p

Correlation analyses.

<p>Scatterplots display correlations between the estimated beta values in the right anterior insular cortex (MNI coordinates (x = 39, y = 15, z = 3)) and AMP.NS.SCR (range-corrected) in response to H100 (a), subjective arousal ratings for H100 (b), and the Anxiety Sensitivity Index (c). Pearson correlation coefficients (R) are given in the plots. Estimated ß-values for the four regressors of interest (H50, H100, T50, T100) were extracted and added so that the t-contrast H50+H100 > T50+T100 was replicated, i.e. difference values were entered into correlation analyses. ** p < 0.01 (Bonferroni-corrected).</p

Design of the heartbeat paradigm.

<p>Upper half: Illustration of the block design structure (four conditions with four blocks of stimulation each, separated by 30 s baseline periods). Order of blocks was randomized across subjects. Lower half: Temporal sequence within one condition, using the example of the heartbeat condition. Hearts illustrate the heartbeat condition; clefs illustrate the sinus tone condition.</p

Submarine Hydrothermal Discharge and Fluxes of Dissolved Fe and Mn, and He Isotopes at Brothers Volcano Based on Radium Isotopes

Hydrothermal venting is an important transfer process of energy and elements between the Earth&rsquo;s solid material and the oceans. Compared to mid-ocean-ridge hydrothermal vent fields, those at intra-oceanic island arcs are typically in shallower water depth and have a more variable geochemical fluid composition. Biologically essential trace elements (such as Fe and Mn) are generally elevated in fluids of both deep and shallow hydrothermal vent fields, while vents at shallower water depth influence the photic zone more directly and thus are potentially more relevant for marine primary productivity. However, fluid flux estimations of island arc hydrothermal systems into the surrounding water column are scarce. This study (I) presents a method based on short-lived radium isotopes to estimate submarine hydrothermal discharge (SHD), (II) applies this method at Brothers volcano in the southern Kermadec arc, located northeast of New Zealand, and (III) gives dissolved Fe, Mn and He isotope flux estimates for the Earth&acute;s longest intra-oceanic island arc, the Kermadec arc. The comparison between measured inert He isotope concentrations in the plume with calculated concentrations based on Ra isotopes matched reasonably well, which supports the use of a Ra-based discharge model. Overall, this study represents a novel approach to assess fluid and thus trace element fluxes from one hydrothermal vent field, which can be applied in future studies on various hydrothermal systems to improve geochemical models of element cycling in the ocean