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Kasten, F. H.

Publications and source records attributed to Kasten, F. H..

9 recordsLinked to original sources

The causal role of β-oscillations in maintaining perception-action representations

The binding of perception and action features into common representations, so-called event files, is a core mechanism supporting goal-directed behavior. Recent work using electroencephalography has presented correlational evidence linking the maintenance of perception-action representations to oscillatory activity in the {beta}-frequency range. Here, we used transcranial alternating current stimulation (tACS) to test whether {beta}-oscillations play a causal role in event-file maintenance. Participants performed a distractor-response binding task with a sequential prime-probe structure while receiving either active {beta}-tACS over the left occipito-parietal cortex or a novel shunt stimulation designed to produce comparable sensory effects but substantially weaker cortical stimulation. Prime-probe intervals were varied to manipulate event-file maintenance. {beta}-tACS did not modulate behavioral binding effects during stimulation. However, we observed a significant aftereffect on behavioral distractor-response binding after stimulation. This effect was restricted to short prime-probe intervals, where event files are typically still available, and was absent at longer intervals, where event files commonly decay. These findings provide causal evidence that {beta}-oscillations contribute to the stabilization of perception-action representations over time. More broadly, they support the view that {beta}-oscillations help maintain the current cognitive-motor state and preserve the status-quo in action control.

neuroscience↗

Decomposing the effects of alpha-tACS on brain oscillations and aperiodic 1/f activity

BackgroundAftereffects of transcranial alternating current stimulation (tACS) are usually analyzed with a focus on the individual frequency band, thereby neglecting broadband spectral components. Recently, it was shown that the broadband spectrum, which exhibits a 1/f-like characteristic, is functionally relevant. Objective/HypothesisThe goal of this study was a spectral parameterization of brain activity into oscillatory alpha activity and aperiodic 1/f components before and after tACS and sham stimulation. It was expected that the broadband spectrum will not be differentially influenced by 20-min of tACS at individual -frequency (IAF) in comparison to sham. Additionally, it was expected that the tACS aftereffect on the -band can still be observed, even when controlling for 1/f activity differences. MethodsWe performed a re-analysis of a recently published resting-state tACS-magnetoencephalography (MEG) data set. Parameterization of the frequency spectrum was computed with the fitting-oscillations-and-one-over-F (FOOOF) algorithm. The intercept as well as the slope parameter of the aperiodic 1/f fit was extracted. Data was analyzed in sensor space with a focus on magnetometers. Comparison of changes in -band power and 1/f activity was performed with non-parametric cluster-based random permutation tests. ResultsThe tACS aftereffect survived the 1/f-correction. The previously observed natural rise in alpha oscillations over time independent of experimental conditions could not be replicated. However, differences in aperiodic parameters over time were observed. Especially, the intercept parameter increased from pre to post stimulation to a similar degree in both conditions. ConclusionIt is imperative to correct for the aperiodic 1/f spectral component when analyzing aftereffects of brain stimulation on brain oscillations.

neuroscience↗

Opposing neural processing modes alternate rhythmically during sustained auditory attention

During continuous tasks, humans show spontaneous fluctuations in performance, putatively caused by varying attentional resources allocated to process external information. If neural resources are used to process other, presumably "internal" information, sensory input can be missed and explain an apparent dichotomy of "internal" versus "external" attention. In the current study, we extracted presumed neural signatures of these attentional modes in human electroencephalography (EEG): neural entrainment and -oscillations ([~]10-Hz), linked to the processing and suppression of sensory information, respectively. We tested whether they exhibit structured fluctuations over time, while listeners attended to an ecologically relevant stimulus like speech and completed a task that required full and continuous attention. Results showed an antagonistic relation between neural entrainment to speech and spontaneous -oscillations in two distinct brain networks - one specialized in the processing of external information, the other reminiscent of the dorsal attention network. These opposing neural modes underwent slow, periodic fluctuations around [~]0.07 Hz and were related to the detection of auditory targets. Our study might have tapped into a general attentional mechanism that is conserved across species and has important implications for situations in which sustained attention to sensory information is critical. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/560684v3_ufig1.gif" ALT="Figure 1"> View larger version (48K): org.highwire.dtl.DTLVardef@43f7d9org.highwire.dtl.DTLVardef@44fd09org.highwire.dtl.DTLVardef@1407de9org.highwire.dtl.DTLVardef@10a7acc_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

Localizing the Sources of Modulations of the P3m Component by Task Difficulty

1The P3m is a late component of the event-related field (ERF) and is assumed to reflect the allocation of resources in various cognitive domains. The amplitude of the P3m can be affected by several task parameters, like stimulus probability, inter-stimulus interval and task difficulty. The task difficulty can alter the P3m amplitude, depending on which mechanisms are involved. The sources of the P3m are located in several brain areas, suggesting a widespread network generating the P3m. Which of these sources of the P3m give rise to the task-difficulty induced amplitude modulation are not well investigated. However, localizing these sources could pave the way for intervention studies with non-invasive brain stimulation methods, which might be suitable to modulate the pathologically altered P3m emerging in various psychiatric and neurodevelopmental disorders. We designed a MEG-study with a visual oddball-like task with two different task difficulties to 1) show decreased P3m amplitudes induced by increased task difficulty and 2) estimate the sources of this P3m modulation. Additionally, the influence of the increased task difficulty on behavioral outcomes were analyzed. The P3m amplitude decreased significantly in the hard condition compared to easy condition. Furthermore, the hit rate for standard trials decreased significantly, while the reaction times increased for both, targets and standards. For this specific visual oddball-like task, the sources of the task difficulty dependent P3m amplitude modulation are located in the centro-parietal regions.

neuroscience↗

Characterizing Low-Frequency Artifacts During Transcranial Temporal Interference Stimulation (tTIS)

Transcranial alternating current stimulation (tACS) is a well-established brain stimulation technique to modulate human brain oscillations. However, due to the strong electro-magnetic artifacts induced by the stimulation current, the simultaneous measurement of tACS effects during neurophysiological recordings in humans is challenging. Recently, transcranial temporal interference stimulation (tTIS) has been introduced to stimulate neurons at depth non-invasively. During tTIS, two high-frequency sine waves are applied, that interfere inside the brain, resulting in amplitude modulated waveforms at the target frequency. Given appropriate hardware, we show that neurophysiological data during tTIS may be acquired without stimulation artifacts at low-frequencies. However, data must be inspected carefully for possible low-frequency artifacts. Our results may help to design experimental setups to record brain activity during tTIS, which may foster our understanding of its underlying mechanisms.

neuroscience↗

The hidden state-dependency of transcranial alternating current stimulation (tACS)

Non-invasive techniques to electrically stimulate the brain such as transcranial direct and alternating current stimulation (tDCS/tACS) are increasingly used in human neuroscience and offer potential new avenues to treat brain disorders. However, their often weak and variable effects have also raised concerns in the scientific community. A possible factor influencing the efficacy of these methods is the dependence on brain-states. Here, we utilized Hidden Markov Models (HMM) to decompose concurrent tACS-magnetoencephalography data into transient brain-states with distinct spatial, spectral and connectivity profiles. We found that out of four spontaneous brain-states only one was susceptible to tACS. No or only marginal effects were found in the remaining states. TACS did not influence the time spent in each state. Our results suggest, that tACS effects may be mediated by a hidden, spontaneous state-dependency and provide novel insights to the changes in oscillatory activity underlying aftereffects of tACS.

neuroscience↗

Integrating electric field modelling and neuroimaging to explain variability of low intensity tES effects

Understanding variability of transcranial electrical stimulation (tES) effects is one of the major challenges in the brain stimulation community. Promising candidates to explain this variability are individual anatomy and the resulting differences of electric fields inside the brain. We integrated individual simulations of electric fields during tES with source-localization to predict variability of transcranial alternating current stimulation (tACS) aftereffects on -oscillations. In two experiments, participants received 20 minutes of either -tACS (1 mA) or sham stimulation. Magnetoencephalogram was recorded for 10 minutes before and after stimulation. tACS caused a larger power increase in the -band as compared to sham. The variability of this effect was significantly predicted by measures derived from individual electric field modelling. Our results directly link electric field variability to variability of tACS outcomes, stressing the importance of individualizing stimulation protocols and providing a novel approach to analyze tACS effects in terms of dose-response relationships.

neuroscience↗

Facilitated event-related power-modulations during transcranial alternating current stimulation (tACS) revealed by concurrent tACS-MEG

Non-invasive approaches to modulate oscillatory activity in the brain receive growing popularity in the scientific community. Transcranial alternating current stimulation (tACS) has been shown to modulate neural oscillations in a frequency specific manner. Due to a massive stimulation artifact at the targeted frequency, only little is known about effects of tACS during stimulation. I.e. it remains unclear how the continuous application of tACS affects event-related oscillations during cognitive tasks. Depending on whether tACS merely affects pre- or post-stimulus oscillations or both, stimulation can alter patterns of event-related oscillatory dynamics in various directions or may not affect them at all. Thus, knowledge about these directions is crucial to plan, predict and understand outcomes of solely behavioral tACS experiments. Here, a recently proposed procedure to suppress tACS artifacts by projecting MEG data into source space using spatial filtering was utilized to recover event-related power modulations in the alpha band during a mental rotation task. MEG of twenty-five volunteers was continuously recorded. After 10 minutes of baseline measurement, they received either 20 minutes of tACS at individual alpha frequency or sham stimulation. Another 40 minutes of MEG were acquired thereafter. Data were projected into source space and carefully examined for residual artifacts. Results revealed strong facilitation of event-related power modulations in the alpha band during tACS application. Data provide first direct evidence, that tACS does not counteract top-down suppression of intrinsic oscillations, but rather enhances pre-existent power modulations within the range of the individual alpha (=stimulation) frequency.\n\nSignificanceTranscranial alternating current stimulation (tACS) is increasingly used in cognitive neuroscience to study the causal role of brain oscillations and cognition. However, online effects of tACS so far largely remain a black box due to an intense electromagnetic artifact encountered during stimulation. The current study is the first to employ a spatial filtering approach to recover and systematically study event-related oscillatory dynamics during tACS, which can potentially be altered in various directions. TACS facilitated pre-existing patterns of oscillatory dynamics during the employed mental rotation task, but does not counteract or overwrite them. In addition, control analysis and a measure to quantify tACS artifact suppression are provided that can enrich future studies investigating tACS online effects.

neuroscience↗

Non-linear transfer characteristics of stimulation and recording hardware account for spurious low-frequency artifacts during amplitude modulated transcranial alternating current stimulation (AM-tACS)

Amplitude modulated transcranial alternating current stimulation (AM-tACS) has been recently proposed as a possible solution to overcome the pronounced stimulation artifact encountered when recording brain activity during tACS. In theory, AM-tACS does not entail power at its modulating frequency, thus avoiding the problem of spectral overlap between brain signal of interest and stimulation artifact. However, the current study demonstrates how weak non-linear transfer characteristics inherent in stimulation and recording hardware can reintroduce spurious artifacts at the modulation frequency. The input-output transfer functions (TFs) of different stimulation setups were measured. The setups included basic recordings of signal-generator and stimulator outputs as well as M/EEG phantom measurements. 6th-degree polynomial regression models were fitted to model the input-output TFs of each setup. The resulting TF models were applied to digitally generated AM-tACS signals to predict the location of spurious artifacts in the spectrum. All four setups measured for the study exhibited low-frequency artifacts at the modulation frequency and its harmonics when recording AM-tACS. Fitted TF models showed non-linear contributions significantly different from zero (all p < .05) and successfully predicted the frequency of artifacts observed in AM-signal recordings. Results suggest that even weak non-linearities of stimulation and recording hardware can lead to spurious artifacts at the modulation frequency and its harmonics. Thus, findings emphasize the need for more linear stimulation devices for AM-tACS and careful analysis procedures, which take into account these low-frequency artifacts to avoid confusion with effects of AM-tACS on the brain.

neuroscience↗