Biology subjects

Klaus, J.

Publications and source records attributed to Klaus, J..

6 recordsLinked to original sources

bioRxiv2025

From stomach to striatum: Ghrelin infusions increase work for rewards

Preclinical evidence demonstrates that gut signals influence motivated behavior through the dopaminergic system. However, translational research in humans is scarce, and it is not known if surges of the stomach-derived hormone ghrelin acutely boost motivation via dopamine transmission. To close this gap, we investigated the effects of acyl ghrelin infusions (vs. saline) on instrumental work for rewards, brain responses, and dopamine transmission in healthy adults in a double-blind, randomized and placebo-controlled crossover study with [11C]raclopride PET-fMRI. In line with preclinical findings, ghrelin enhanced hunger sensations (p = .007), and effort for food and small rewards. Crucially, ghrelin enhanced functional connectivity between the hypothalamus and the striatum (NAcc: pSVC = .016), as well as within the striatum (NAcc<>Putamen: pSVC = .001), pointing to an enhanced coupling between homeostatic and motivational circuits. However, ghrelin did not alter dopamine binding potential (reflecting changes in endogenous tone), but boosted task-free phasic pulses of the NAcc BOLD signal (p = .020), which were negatively associated with binding potential (p = .034). During the task, ghrelin increased cue- (precentral gyrus: pFWE = .003) and effort-evoked brain responses (e.g., VTA/SN: psvc = .002) in accordance with increases in motivation. Together, these findings recapitulate preclinical work that ghrelin primarily boosts phasic dopamine release, reflecting enhanced incentive salience of food and smaller rewards. This highlights the potential of targeting gut-brain interactions to improve motivational symptoms, such as loss of appetite or anhedonia. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=131 SRC="FIGDIR/small/691596v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@4321e6org.highwire.dtl.DTLVardef@166bda5org.highwire.dtl.DTLVardef@2ca69dorg.highwire.dtl.DTLVardef@16e93a9_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2020

Non-invasive vagus nerve stimulation boosts mood recovery after effort exertion

Mood plays an important role in our life which is illustrated by the disruptive impact of aberrant mood states in depression. Although vagus nerve stimulation (VNS) has been shown to improve symptoms of depression, the exact mechanism is still elusive, and it is an open question whether non-invasive VNS could be used to swiftly and robustly improve mood. Here, we investigated the effect of left- and right-sided transcutaneous auricular VNS (taVNS) versus a sham control condition on mood after exertion of physical and cognitive effort in 82 healthy participants (randomized cross-over design). Using linear mixed-effects and hierarchical Bayesian analyses of mood ratings, we found that 90 min of either left-sided or right-sided taVNS improved positive mood (b = 5.11, 95% credible interval, CI [1.39, 9.01], 9.6% improvement relative to the mood intercept, BF10= 7.69, pLME = .017), yet only during the post stimulation phase. Moreover, lower baseline scores of positive mood were associated with greater taVNS-induced improvements in motivation (r = -.42, 95% CI [-.58, -.21], BF10 = 249). We conclude that taVNS boosts mood after a prolonged period of effort exertion with concurrent stimulation and that acute motivational effects of taVNS are partly dependent on initial mood states. Collectively, our results show that taVNS may help quickly improve affect after a mood challenge, potentially by modulating interoceptive signals contributing to reappraisal of effortful behavior. This suggests that taVNS could be a useful add-on to current behavioral therapies.

neuroscience↗

bioRxiv2019

Transient perturbation of the left temporal cortex evokes plasticity-related reconfiguration of the lexical network

Language impairment is common after left-hemisphere damage. However, the involvement of perilesional and homologous contralateral regions in compensating for left-sided lesions remains poorly understood. The aim of this study was to examine acute organizational changes in brain activity related to conceptual and lexical retrieval in unimpaired language production following transient disruption of the left middle temporal gyrus (MTG). In a randomized singleblind within-subject experiment, we recorded the electroencephalogram from sixteen healthy participants during a context-driven picture-naming task. Prior to the task, the left MTG was perturbed with real neuronavigated continuous theta-burst stimulation (cTBS) or sham stimulation. During the task, participants read lead-in sentences that created a constraining (e.g. "The farmer milks the") or non-constraining context (e.g. "The farmer buys the"). The last word was shown as a picture that participants had to name (e.g. "cow"). Replicating behavioral studies, participants were overall faster in naming pictures following a constraining relative to a non-constraining context, but this effect did not differ between real and sham cTBS. Real cTBS, however, increased overall error rates compared to sham cTBS. In line with previous studies, we observed a decrease in alpha-beta (8-24 Hz) oscillatory power for constraining relative to non-constraining contexts over left temporal-parietal cortex after participants received sham cTBS. However, following real cTBS, this decrease extended towards left prefrontal regions associated with both domain-general and domain-specific control mechanisms. Our findings provide evidence that immediately after the disruption of the left MTG, the lexical-semantic network is able to quickly reconfigure, also recruiting domain-general regions.

neuroscience↗

bioRxiv2017

The Role of Left Dorsolateral Prefrontal Cortex in Language Processing

In addition to the role of left frontotemporal areas in language processing, there is increasing evidence that language comprehension and production require control and working memory resources involving the left dorsolateral prefrontal cortex (DLPFC). The aim of this study was to investigate the role of the left DLPFC in both language comprehension and production. In a double-blind, sham-controlled crossover experiment, thirty-two participants received cathodal or sham transcranial direct current stimulation (tDCS) to the left DLPFC while performing a language comprehension and a language production task. Results showed that cathodal tDCS increases reaction times in the language comprehension task, but decreases naming latencies in the language production task. However, additional analyses revealed that the polarity of tDCS effects was highly correlated across tasks, implying differential individual susceptibility to the effect of tDCS within participants. Overall, our findings demonstrate that left DLPFC is part of the complex cortical network associated with language processing.

neuroscience↗

bioRxiv2017

Putting Focus on Transcranial Direct Current Stimulation in Language Production Studies

ObjectivePrevious language production studies targeting the inferior frontal and superior temporal gyrus using anodal tDCS have provided mixed results. Part of this heterogeneity may be explained by limited target region focality of conventionally used electrode montages. We examined the focality of conventionally and alternative electrode montages.\n\nMethodsElectrical field distributions of anodal tDCS targeting IFG and pSTG were simulated in conventional setups (anodal electrode over IFG/pSTG, reference electrode over right supraorbital region) and an alternative electrode montage in four different brains.\n\nResultsConventional montages showed maximum field strengths outside of the target regions. Results from alternative electrode montages showed that focality of tDCS could be improved by adjustments in electrode size and placement.\n\nConclusionsHeterogeneity of findings of language production studies deploying conventional tDCS montages may in part be explained by diffuse electrical field distributions. Alternative montages may improve focality and provide more unequivocal results.\n\nSignificanceReliability of tDCS in language production research, both in basic and applied fields, can be improved by adopting different electrode montages which target the region of interest in a more direct way.

neuroscience↗

bioRxiv2017

Non-Invasive Brain Stimulation to Investigate Language Production in Healthy Speakers: A Review and Meta-Analysis

Non-invasive brain stimulation (NIBS) has become a common method to study the interrelations between the brain and language functioning. This meta-analysis examined the efficacy of transcranial magnetic stimulation (TMS) and direct current stimulation (tDCS) in the study of language production in healthy volunteers. Forty-five effect sizes from 30 studies which investigated the effects of NIBS on picture naming or verbal fluency in healthy participants were meta-analysed. Further sub-analyses investigated potential influences of stimulation type, control, target site, task, online vs. offline application, and current density of the target electrode. Random effects modelling showed a small, but reliable effect of NIBS on language production. Subsequent analyses indicated larger weighted mean effect sizes for TMS as compared to tDCS studies. No statistical differences for the other sub-analyses were observed. We conclude that NIBS is a useful method for neuroscientific studies on language production in healthy volunteers.

neuroscience↗