Lateral prefrontal anodal transcranial direct current stimulation augments resolution of auditory perceptual-attentional conflicts

Transcutaneous Auricular Vagus Nerve Stimulation for Visually Induced Motion Sickness: An eLORETA Study

Transcutaneous auricular vagus nerve stimulation (taVNS), a non-invasive form of electrical brain stimulation, has shown potent therapeutic potential for a wide spectrum of conditions. How taVNS influences the characterization of motion sickness - a long mysterious syndrome with a polysymptomatic onset - remains unclear. Here, to examine taVNS-induced effects on brain function in response to motion-induced nausea, 64-channel electroencephalography (EEG) recordings from 42 healthy participants were analyzed; collected during nauseogenic visual stimulation concurrent with taVNS administration, in a crossover randomized sham-controlled study. Cortical neuronal generators were estimated from the obtained EEG using exact low-resolution brain electromagnetic tomography (eLORETA). While both sham and taVNS increased insula activation during electrical stimulation, compared to baseline, taVNS additionally augmented middle frontal gyrus neuronal activity. Following taVNS, brain regions including the supramarginal, parahippocampal, and precentral gyri were activated. Contrasting sham, taVNS markedly increased activity in the middle occipital gyrus during stimulation. A repeated-measures ANOVA showed that taVNS reduced motion sickness symptoms. This reduction in symptoms correlated with taVNS-induced neural activation. Our findings provide new insights into taVNS-induced brain changes, during and after nauseogenic stimuli exposure, including accompanying behavioral response. Together, these findings suggest that taVNS has promise as an effective neurostimulation tool for motion sickness management.

Does chronic use of amphetamine-type stimulants impair interference control? - A meta-analysis

In substance use and addiction, inhibitory control is key to ignoring triggers, withstanding craving and maintaining abstinence. In amphetamine-type stimulant (ATS) users, most research focused on behavioral inhibition, but largely neglected the equally important subdomain of cognitive interference control. Given its crucial role in managing consumption, we investigated the relationship between interference control and chronic ATS use in adults. A database search (Pubmed & Web of Science) and relevant reviews were used to identify eligible studies. Effect sizes were estimated with random effects models. Subgroup, meta-regression, and sensitivity analyses explored heterogeneity in effect sizes. We identified 61 studies (53 datasets) assessing interference control in 1873 ATS users and 1905 controls. Findings revealed robust small effect sizes for ATS-related deficits in interference control, which were mainly seen in methamphetamine, as compared to MDMA users. The differential effects are likely due to tolerance-induced dopaminergic deficiencies (presumably most pronounced in methamphetamine users). Similarities between different ATS could be due to noradrenergic deficiencies; but elucidating their functional role in ATS users requires further/more research.

Auricular Transcutaneous Vagus Nerve Stimulation Diminishes Alpha-Band-Related Inhibitory Gating Processes During Conflict Monitoring in Frontal Cortices

BACKGROUND

Pursuing goals is compromised when being confronted with interfering information. In such situations, conflict monitoring is important. Theoretical considerations on the neurobiology of response selection and control suggest that auricular transcutaneous vagus nerve stimulation (atVNS) should modulate conflict monitoring. However, the neurophysiological-functional neuroanatomical underpinnings are still not understood.

METHODS

AtVNS was applied in a randomized crossover study design (n = 45). During atVNS or sham stimulation, conflict monitoring was assessed using a Flanker task. EEG data were recorded and analyzed with focus on theta and alpha band activity. Beamforming was applied to examine functional neuroanatomical correlates of atVNS-induced EEG modulations. Moreover, temporal EEG signal decomposition was applied to examine different coding levels in alpha and theta band activity.

RESULTS

AtVNS compromised conflict monitoring processes when it was applied at the second appointment in the crossover study design. On a neurophysiological level, atVNS exerted specific effects because only alpha-band activity was modulated. Alpha-band activity was lower in middle and superior prefrontal regions during atVNS stimulation and thus lower when there was also a decline in task performance. The same direction of alpha-band modulations was evident in fractions of the alpha-band activity coding stimulus-related processes, stimulus-response translation processes, and motor response-related processes.

CONCLUSIONS

The combination of prior task experience and atVNS compromises conflict monitoring processes. This is likely due to reduction of the alpha-band-associated inhibitory gating process on interfering information in frontal cortices. Future research should pay considerable attention to boundary conditions affecting the direction of atVNS effects.

Neurophysiological and functional neuroanatomical coding of statistical and deterministic rule information during sequence learning

Humans are capable of acquiring multiple types of information presented in the same information stream. It has been suggested that at least two parallel learning processes are important during learning of sequential patterns-statistical learning and rule-based learning. Yet, the neurophysiological underpinnings of these parallel learning processes are not fully understood. To differentiate between the simultaneous mechanisms at the single trial level, we apply a temporal EEG signal decomposition approach together with sLORETA source localization method to delineate whether distinct statistical and rule-based learning codes can be distinguished in EEG data and can be related to distinct functional neuroanatomical structures. We demonstrate that concomitant but distinct aspects of information coded in the N2 time window play a role in these mechanisms: mismatch detection and response control underlie statistical learning and rule-based learning, respectively, albeit with different levels of time-sensitivity. Moreover, the effects of the two learning mechanisms in the different temporally decomposed clusters of neural activity also differed from each other in neural sources. Importantly, the right inferior frontal cortex (BA44) was specifically implicated in visuomotor statistical learning, confirming its role in the acquisition of transitional probabilities. In contrast, visuomotor rule-based learning was associated with the prefrontal gyrus (BA6). The results show how simultaneous learning mechanisms operate at the neurophysiological level and are orchestrated by distinct prefrontal cortical areas. The current findings deepen our understanding on the mechanisms of how humans are capable of learning multiple types of information from the same stimulus stream in a parallel fashion.

The effects of stress and transcranial direct current stimulation (tDCS) on working memory: A randomized controlled trial

Recent reviews of transcranial direct current stimulation (tDCS) show limited support for its initially cited enhancing effects on working memory (WM). They highlight the need for additional research, assessing the specific circumstances that optimize stimulation outcome. Social stress is an attractive candidate in this regard, as it affects WM and is mediated by prefrontal cortex activity; tDCS that targets these neuronal networks may, therefore, interact with social stress to affect WM. Our objective was to explore the interaction between social stress and tDCS on WM performance in a healthy cohort, 69 female participants were randomized to four experimental conditions (i.e., 2 × 2 design): stimulation (dlPFC tDCS vs. sham stimulation) and stress manipulation (Trier Social Stress Test [TSST] procedure vs. a friendly control TSST). Participants' attention, WM (assessed using an n-back task), and subjective/objective indicators of stress were assessed. A significant Stimulation × Stress Manipulation interaction was found, F(1, 65) = 6.208, p = .015, suggesting that active tDCS may increase WM performance in the no-stress conditions, while decreasing it under stress. Follow-up analyses of variance, however, were not significant (i.e., ps=.083 / .093), and Bayesian analyses were inconclusive. In conclusion, stress seems to be a crucial factor in determining the effects of tDCS, and tDCS may have an enhancing effect on WM at lower levels of stress, while being detrimental at higher stress levels (i.e., reversing the direction of effect). Possible theoretical underpinnings of the findings are discussed, while acknowledging the need for further research.

The neurobiology of prefrontal transcranial direct current stimulation (tDCS) in promoting brain plasticity: A systematic review and meta-analyses of human and rodent studies

The neurobiological mechanisms underlying prefrontal transcranial direct current stimulation (tDCS) remain elusive. Randomized, sham-controlled trials in humans and rodents applying in vivo prefrontal tDCS were included to explore whether prefrontal tDCS modulates resting-state and event-related functional connectivity, neural oscillation and synaptic plasticity. Fifty studies were included in the systematic review and 32 in the meta-analyses. Neuroimaging meta-analysis indicated anodal prefrontal tDCS significantly enhanced bilateral median cingulate activity [familywise error (FWE)-corrected p < .005]; meta-regression revealed a positive relationship between changes in median cingulate activity after tDCS and current density (FWE-corrected p < .005) as well as electric current strength (FWE-corrected p < .05). Meta-analyses of electroencephalography and magnetoencephalography data revealed nonsignificant changes (ps > .1) in both resting-state and event-related oscillatory power across all frequency bands. Applying anodal tDCS over the rodent hippocampus/prefrontal cortex enhanced long-term potentiation and brain-derived neurotrophic factor expression in the stimulated brain regions (ps <.005). Evidence supporting prefrontal tDCS administration is preliminary; more methodologically consistent studies evaluating its effects on cognitive function that include brain activity measurements are needed.

EEG dynamics and neural generators of psychological flow during one tightrope performance

Psychological “flow” emerges from a goal requiring action, and a match between skills and challenge. Using high-density electroencephalographic (EEG) recording, we quantified the neural generators characterizing psychological “flow” compared to a mindful “stress” state during a professional tightrope performance. Applying swLORETA based on self-reported mental states revealed the right superior temporal gyrus (BA38), right globus pallidus, and putamen as generators of delta, alpha, and beta oscillations, respectively, when comparing “flow” versus “stress”. Comparison of “stress” versus “flow” identified the middle temporal gyrus (BA39) as the delta generator, and the medial frontal gyrus (BA10) as the alpha and beta generator. These results support that “flow” emergence required transient hypo-frontality. Applying swLORETA on the motor command represented by the tibialis anterior EMG burst identified the ipsilateral cerebellum and contralateral sensorimotor cortex in association with on-line control exerted during both “flow” and “stress”, while the basal ganglia was identified only during “flow”.

Anodal transcranial direct current stimulation enhances the efficiency of functional brain network communication during auditory attentional control

Attentional control is crucial for selectively attending to relevant information when our brain is confronted with a multitude of sensory signals. Graph-theoretical measures provide a powerful tool for investigating the efficiency of brain network communication in separating and integrating information. Albeit, it has been demonstrated that anodal transcranial direct current stimulation (atDCS) can boost auditory attention in situations with high control demands, its effect on neurophysiological mechanisms of functional brain network communication in situations when attentional focus conflicts with perceptual saliency remain unclear. This study investigated the effects of atDCS on network connectivity and θ-oscillatory power under different levels of attentional-perceptual conflict. We hypothesized that the benefit of atDCS on network communication efficiency would be particularly apparent in conditions requiring high attentional control. Thirty young adults participated in a dichotic listening task with intensity manipulation, while EEG activity was recorded. In a cross-over design, participants underwent right frontal atDCS and sham stimulations in two separate sessions. Time-frequency decomposition and graph-theoretical analyses of network efficiency (using "small-world" properties) were used to quantify θ-oscillatory power and brain network efficiency, respectively. The atDCS-induced effect on task efficiency in the most demanding condition was mirrored only by an increase in network efficiency during atDCS compared with the sham stimulation. These findings are corroborated by Bayesian analyses. AtDCS-induced performance enhancement under high levels of attentional-perceptual conflicts is accompanied by an increase in network efficiency. Graph-theoretical measures can serve as a metric to quantify the effects of noninvasive brain stimulation on the separation and integration of information in the brain.NEW & NOTEWORTHY As compared with sham stimulation, application of atDCS enhances θ-oscillation-based network efficiency, but it has no impact on θ-oscillation power. Individual differences in θ-oscillation-based network efficiency correlated with performance efficiency under the sham stimulation.

Task experience eliminates catecholaminergic effects on inhibitory control - A randomized, double-blind cross-over neurophysiological study

Catecholaminergic neural transmission plays an important role during the inhibition of prepotent responses. Methylphenidate (MPH) is an important drug that modulates the catecholaminergic system. However, theoretical considerations suggest that the effects of drugs (e.g. MPH) on cognitive control may depend on prior learning effects. Here we investigate this in a conflict-modulated Go/Nogo task and evaluate neurophysiological processes associated with this dynamic using EEG signal decomposition methods and source localization analysis. The behavioral data show that prior learning experiences eliminate effects of MPH on response inhibition processes. On a neurophysiological level, we show that MPH modulates specific processes in medial frontal brain regions. Although MPH seems to consistently modulate neurophysiological processes associated with response inhibition, this is no longer sufficient to modulate behavioral performance once learning or task familiarization processes have taken place. An important consequence of this study finding is that it may be important to adjust MPH dosage depending on learning effects in a specific setting to constantly increase cognitive control functions in that setting. This has important implications for clinical practice, since MPH is the first-line pharmacological therapy in attention-deficit hyperactivity disorder (ADHD). Cross-over study designs with constant doses of MPH can mask effects on cognitive functions. The impact of learning needs careful consideration in cross-over study designs examining catecholaminergic drug effects.

Decoding Stimulus-Response Representations and Their Stability Using EEG-Based Multivariate Pattern Analysis

Goal-directed actions require proper associations between stimuli and response. This has been delineated by cognitive theory, for example, in the theory of event coding framework, which proposes that event files represent such bindings. Yet, how such event file representations are coded on a neurophysiological level is unknown. We close this gap combining temporal electroencephalography (EEG) signal decomposition methods and multivariate pattern analysis (MVPA). We show that undecomposed neurophysiological data is unsuitable to decode event file representations because different aspects of information coded in the neurophysiological signal reveal distinct and partly opposed dynamics in the representational content. This is confirmed by applying MVPA to temporal decomposed EEG data. After intermixed aspects of information in the EEG during response selection have been separated, a reliable examination of the event file’s representational content and its temporal stability was possible. We show that representations of stimulus–response bindings are activated and decay in a gradual manner and that event file representations resemble distributed neural activity. Especially representations of stimulus–response bindings, as well as stimulus-related representations, are coded and reveal temporal stability. Purely motor-related representations are not found in neurophysiological signals during event coding.