Biology subjects

Gundlach, C.

Publications and source records attributed to Gundlach, C..

4 recordsLinked to original sources

bioRxiv2026

Auditory Attention Implements Complementary but Independent Cortical Mechanisms of Enhancement and Suppression

In noisy environments, goal-directed behavior requires the brain to prioritize task-relevant sound and to suppress distraction. While mechanisms of proactive attention in the presence of foreknowledge about targets and distractors are well-characterized, the neural dynamics governing reactive auditory attention in the absence of foreknowledge remain less understood. To fill this gap, we recorded the electroencephalogram (EEG) from N = 34 participants performing an auditory search task. Participants identified an amplitude-modulated spoken target number amid distractor numbers of varying salience. Presenting stimuli from three spatial locations enabled isolation of lateralized electrophysiological responses to targets and distractors. We quantified selection of targets versus distractors by continuously tracking participants cursor movements on a virtual response pad. Behaviorally, the target-directedness of cursor movements (i.e., towardness) increased for target repetitions (positive priming) and decreased when the target was a distractor from the previous trial (negative priming), indicating respective enhancement and suppression. Neurally, lateral targets evoked an N2ac component reflecting reactive enhancement. Importantly, we here demonstrate for the first time in an auditory attention task that distracting sounds evoke an auditory distractor positivity (PD) component. Target enhancement and distractor suppression were largely independent: their neural and behavioral markers were not significantly correlated and they originated from distinct cortical sources. Furthermore, shorter N2ac-but not PD-latencies related to higher towardness. By dissociating neural signatures and behavioral relevance of enhancement and suppression, our findings refine biased-competition models of attention, demonstrating that reactive selection relies on separable mechanisms rather than a single competitive gain process. Significance statementEveryday listening requires the rapid selection of relevant sounds and ignoring distraction, even when there is no prior knowledge of what will be heard. Here, we reveal the neural mechanisms that enable such reactive auditory attention. Combining electroencephalography with continuous measures of behavior, we show that target enhancement and distractor suppression are supported by distinct neural processes, indexed by the N2ac and the auditory PD component. These processes are largely independent, with only enhancement predicting behavior. This dissociation challenges unitary accounts of attentional selection and instead supports models in which separable mechanisms of enhancement and suppression operate in parallel. Our findings provide a mechanistic framework for understanding how the human brain flexibly prioritizes information in complex listening environments.

neuroscience↗

bioRxiv2023

Assessing adverse effects and unspecific effects of transcutaneous spinal direct current stimulation (tsDCS)

BackgroundTranscutaneous spinal direct current stimulation (tsDCS) is a relatively recent method for non-invasively modulating neuronal activity in the human spinal cord. Despite its growing prominence, comprehensive studies addressing its potential adverse effects (AEs) and unspecific effects (UEs) are lacking. ObjectiveIn this study, we conducted a systematic investigation into the potential AEs and UEs of tsDCS in healthy volunteers. MethodsWe used a randomized double-blind within-participant design, employing anodal, cathodal and sham tsDCS of the thoracolumbar spinal cord. Our approach involved a newly-developed structured questionnaire (to assess subjectively-reported AEs) in combination with tsDCS-concurrent recording of skin conductance, cardiac and respiratory activity (to assess UEs in bodily state). ResultsThe most frequently participant-reported AEs were sensations of burning, tingling, and itching, although they were largely described as mild; skin redness (experimenter-reported) occurred even more frequently. Importantly, when comparing AEs between active and sham tsDCS via frequentist and Bayesian analysis approaches, the results were largely in favour of no difference between conditions (with the exception of skin redness). A similar picture emerged for most UE metrics, suggesting that tsDCS does not induce changes in bodily state, at least as measured by our autonomic nervous system metrics. ConclusionWe believe that the strategy employed here could serve as a starting point for a systematic AE and UE assessment in clinical populations, longitudinal designs and when stimulating different spinal sites. Taken together, our results contribute to assessing the tolerability, safety and specificity of tsDCS, in order to further the investigation of spinal cord function in health and disease.

neuroscience↗

bioRxiv2022

Tracing 3D apoplasmic complexity in vascular tissue of live conifer needles by X-ray computed tomography

Architecture and conducting area of vascular elements along conifer needles are fundamentally different from broad leaves. We hypothesised that the needles unique transfusion tissue offers different mechanisms for water allocation and used multimodal imaging to dissect the critical water exchange interfaces in this xerophytic leaf type. Our study examined intact conifer needles with X-ray computed tomography (XCT) and water-soluble tracers, allowing to render the functional 3D structure of the water-filled apoplast and the complementary symplasmic domain inside the bundle sheath. Segmentation of these data, together with fluorescence and electron microscopy of axial phloem and xylem elements along the needle, enabled quantification of the dimensions of the conducting tissue complex. The transfusion tracheid system between the endodermis-type bundle sheath and the axial venation formed a sponge-like apoplast domain. Transfusion parenchyma cell chains bridged this domain not directly but as tortuous symplasmic pathways between bundle sheath and axial phloem, which is nearly exclusively accessible at flanks. The transfusion tissue extends the plasma membrane surface for phloem loading and provides a large volume space. We discuss that this unique tissue plays an important role in the subtle interplay between water uptake/storage and sugar transport that has evolved to cope with desiccation stress.

plant biology↗

bioRxiv2020

Transient amplitude modulation of alpha-band oscillations by short-time intermittent closed-loop tACS

Non-invasive brain stimulation techniques such as transcranial alternating current stimulation (tACS) have recently become extensively utilized due to their potential to modulate ongoing neuronal oscillatory activity and consequently to induce cortical plasticity relevant for various cognitive functions. However, the neurophysiological basis for stimulation effects as well as their inter-individual differences are not yet understood. In the present study we used a closed-loop EEG transcranial alternating current stimulation protocol (EEG-tACS) to examine the modulation of alpha oscillations generated in occipito-parietal areas. In particular, we investigated the effects of a repeated short-time intermittent stimulation protocol (1 s in every trial) applied over the visual cortex (Cz and Oz) and adjusted according to the phase and frequency of visual alpha oscillations on the amplitude of these oscillations. Based on previous findings, we expected higher increases in alpha amplitudes for tACS applied in-phase with ongoing oscillations as compared to an application in anti-phase and this modulation to be present in low-alpha amplitude states of the visual system (eyes opened) but not high (eyes closed). Contrary to our expectations, we found a transient suppression of alpha power in inter-individually derived spatially specific parieto-occipital components obtained via the estimation of spatial filters by using the common spatial patterns approach. The amplitude modulation was independent of the phase relationship between tACS signal and alpha oscillations, and the state of the visual system manipulated via closed- and open-eye conditions. It was also absent in conventionally analyzed single-channel and multi-channel data from an average parieto-occipital region. The fact that the tACS modulation of oscillations was phase-independent suggests that mechanisms driving the effects of tACS may not be explained by entrainment alone, but rather require neuroplastic changes or transient disruption of neural oscillations. Our study also supports the notion that the response to tACS is subject specific, where the modulatory effects are shaped by the interplay between the stimulation and different alpha generators. This favors stimulation protocols as well as analysis regimes exploiting inter-individual differences, such as spatial filters to reveal otherwise hidden stimulation effects and, thereby, comprehensively induce and study the effects and underlying mechanisms of tACS.

neuroscience↗