Transcranial stimulation of alpha oscillations up-regulates the default mode network

The default mode network (DMN) is the most-prominent intrinsic connectivity network, serving as a key architecture of the brain’s functional organization. Conversely, dysregulated DMN is characteristic of major neuropsychiatric disorders. However, the field still lacks mechanistic insights into the regulation of the DMN and effective interventions for DMN dysregulation. The current study approached this problem by manipulating neural synchrony, particularly alpha (8 to 12 Hz) oscillations, a dominant intrinsic oscillatory activity that has been increasingly associated with the DMN in both function and physiology. Using high-definition alpha-frequency transcranial alternating current stimulation (α-tACS) to stimulate the cortical source of alpha oscillations, in combination with simultaneous electroencephalography and functional MRI (EEG-fMRI), we demonstrated that α-tACS (versus Sham control) not only augmented EEG alpha oscillations but also strengthened fMRI and (source-level) alpha connectivity within the core of the DMN. Importantly, increase in alpha oscillations mediated the DMN connectivity enhancement. These findings thus identify a mechanistic link between alpha oscillations and DMN functioning. That transcranial alpha modulation can up-regulate the DMN further highlights an effective noninvasive intervention to normalize DMN functioning in various disorders.

Electroencephalography Correlates of Well-Being Using a Low-Cost Wearable System

Electroencephalography (EEG) alpha asymmetry is thought to reflect crucial brain processes underlying executive control, motivation, and affect. It has been widely used in psychopathology and, more recently, in novel neuromodulation studies. However, inconsistencies remain in the field due to the lack of consensus in methodological approaches employed and the recurrent use of small samples. Wearable technologies ease the collection of large and diversified EEG datasets that better reflect the general population, allow longitudinal monitoring of individuals, and facilitate real-world experience sampling. We tested the feasibility of using a low-cost wearable headset to collect a relatively large EEG database (N = 230, 22–80 years old, 64.3% female), and an open-source automatic method to preprocess it. We then examined associations between well-being levels and the alpha center of gravity (CoG) as well as trait EEG asymmetries, in the frontal and temporoparietal (TP) areas. Robust linear regression models did not reveal an association between well-being and alpha (8–13 Hz) asymmetry in the frontal regions, nor with the CoG. However, well-being was associated with alpha asymmetry in the TP areas (i.e., corresponding to relatively less left than right TP cortical activity as well-being levels increased). This effect was driven by oscillatory activity in lower alpha frequencies (8–10.5 Hz), reinforcing the importance of dissociating sub-components of the alpha band when investigating alpha asymmetries. Age was correlated with both well-being and alpha asymmetry scores, but gender was not. Finally, EEG asymmetries in the other frequency bands were not associated with well-being, supporting the specific role of alpha asymmetries with the brain mechanisms underlying well-being levels. Interpretations, limitations, and recommendations for future studies are discussed. This paper presents novel methodological, experimental, and theoretical findings that help advance human neurophysiological monitoring techniques using wearable neurotechnologies and increase the feasibility of their implementation into real-world applications.

The hippocampus as the switchboard between perception and memory

Adaptive memory recall requires a rapid and flexible switch from external perceptual reminders to internal mnemonic representations. However, owing to the limited temporal or spatial resolution of brain imaging modalities used in isolation, the hippocampal–cortical dynamics supporting this process remain unknown. We thus employed an object-scene cued recall paradigm across two studies, including intracranial electroencephalography (iEEG) and high-density scalp EEG. First, a sustained increase in hippocampal high gamma power (55 to 110 Hz) emerged 500 ms after cue onset and distinguished successful vs. unsuccessful recall. This increase in gamma power for successful recall was followed by a decrease in hippocampal alpha power (8 to 12 Hz). Intriguingly, the hippocampal gamma power increase marked the moment at which extrahippocampal activation patterns shifted from perceptual cue toward mnemonic target representations. In parallel, source-localized EEG alpha power revealed that the recall signal progresses from hippocampus to posterior parietal cortex and then to medial prefrontal cortex. Together, these results identify the hippocampus as the switchboard between perception and memory and elucidate the ensuing hippocampal–cortical dynamics supporting the recall process.

EEG evidence for the effective proactive control of emotional distraction

<p>Recent behavioural studies using an emotional flanker task have found that task-irrelevent emotional images are more distracting than neutral images under infrequent, but not frequent, distractor conditions.It has been proposed the effective control of distraction in the high distractor frequency condition may be due to a shift to a proactive control strategy, whereby a potential distraction is anticipated and minimised in advance. However, although it is well established that proactive control is effective at reducingneutral distraction, it is not yet clear whether emotional distraction can be effectively proactively controlled. In this thesis, I used EEG to measure pre-stimulus indices of proactive control in order to determine whether proactive control is responsible for the effective control of emotional and neutral distraction in the high distractor frequency condition, as well asto examine whether proactive control differs according whether a neutral or emotional distraction is anticipated.In addition to replicating the previous behavioural findings, posterior EEG alpha was found to be tonically suppressed in the high compared to low distractor frequency condition, strongly supporting the hypothesis that proactive control was engaged in the high distractor frequency condition. By contrast, there was no difference in phasic alpha suppression (i.e., the drop in alpha in response to fixation onset) between conditions, indicating that the more effective control of distraction in the high frequency distractor conditions was due to a sustained proactive control strategy, rather than greater trial-by-trial preparation to attend to the target. In addition, no alpha lateralisation was found, indicating the mechanisms by which distraction was proactively controlled did not include the preparatory suppression of expected distractor locations. Finally, tonic alpha did not differ according to the expected distractor valence, but phasic alpha suppression was more pronounced when negative, compared to neutral or positive, distractors were expected, independent of distractor frequency condition. This suggests proactive control was also used to some extent in the low distractor frequency condition, but more importantly also provides initial evidence that the proactive control of negative distraction may be unique. Taken together, my findings provide compelling evidence that emotional distraction can be effectively proactively controlled. Future research is needed to determine the mechanisms by which this occurs, and whether the proactive control of emotional distraction is particularly effortful.</p>

EEG evidence for the effective proactive control of emotional distraction

<p>Recent behavioural studies using an emotional flanker task have found that task-irrelevent emotional images are more distracting than neutral images under infrequent, but not frequent, distractor conditions.It has been proposed the effective control of distraction in the high distractor frequency condition may be due to a shift to a proactive control strategy, whereby a potential distraction is anticipated and minimised in advance. However, although it is well established that proactive control is effective at reducingneutral distraction, it is not yet clear whether emotional distraction can be effectively proactively controlled. In this thesis, I used EEG to measure pre-stimulus indices of proactive control in order to determine whether proactive control is responsible for the effective control of emotional and neutral distraction in the high distractor frequency condition, as well asto examine whether proactive control differs according whether a neutral or emotional distraction is anticipated.In addition to replicating the previous behavioural findings, posterior EEG alpha was found to be tonically suppressed in the high compared to low distractor frequency condition, strongly supporting the hypothesis that proactive control was engaged in the high distractor frequency condition. By contrast, there was no difference in phasic alpha suppression (i.e., the drop in alpha in response to fixation onset) between conditions, indicating that the more effective control of distraction in the high frequency distractor conditions was due to a sustained proactive control strategy, rather than greater trial-by-trial preparation to attend to the target. In addition, no alpha lateralisation was found, indicating the mechanisms by which distraction was proactively controlled did not include the preparatory suppression of expected distractor locations. Finally, tonic alpha did not differ according to the expected distractor valence, but phasic alpha suppression was more pronounced when negative, compared to neutral or positive, distractors were expected, independent of distractor frequency condition. This suggests proactive control was also used to some extent in the low distractor frequency condition, but more importantly also provides initial evidence that the proactive control of negative distraction may be unique. Taken together, my findings provide compelling evidence that emotional distraction can be effectively proactively controlled. Future research is needed to determine the mechanisms by which this occurs, and whether the proactive control of emotional distraction is particularly effortful.</p>

The Right Lateral Prefrontal Cortex Impacts Control Perception as a Function of Probabilistic Stimulus Processing

Being able to control inner and environmental states is a basic need of living creatures. Control perception (CP) itself may be neurally computed as the subjective ratio of outcome probabilities given the presence and the absence of behavior. If behavior increases the perceived probability of a given outcome, action-outcome contingency is met, and CP may emerge. Nonetheless, in regard of this model, not much is known on how the brain processes CP from these information. This study uses low-intensity transcranial focused ultrasound neuromodulation in a randomized-controlled doubleblind cross-over design to investigate the impact of the right inferior frontal gyrus on this process. Fourty healthy participants visited the laboratory twice (once in a sham, once in a neuromodulation condition) and rated their control perception regarding a classical control illusion task. EEG alpha and theta power density were analyzed in a hierarchical single trial based mixed modeling approach. Results indicate that the right lateral PFC modulates action-outcome learning by providing stochastic information about the situation with increased alpha responses during low control situations (in which the ratio of probabilities is zero). Furthermore, this alpha response was found to modulate mid-frontal theta by altering its relationship with self-reported effort and worrying. These data provide evidencefor right lateral PFC mediated probabilistic stimulus processing during the emergence of CP.

Functional but not obligatory link between microsaccades and neural modulation by covert spatial attention

Covert spatial attention is associated with spatially specific modulation of neural activity as well as with directional biases in fixational eye-movements known as microsaccades. Recently, this link has been suggested to be obligatory, such that modulation of neural activity by covert spatial attention occurs only when paired with microsaccades toward the attended location. Here we revisited this link between microsaccades and neural modulation by covert spatial attention in humans. We investigated spatial modulation of 8-12 Hz EEG alpha activity and microsaccades in a context with no incentive for overt gaze behaviour: when attention is directed internally within the spatial layout of visual working memory. In line with a common attentional origin, we show that spatial modulations of alpha activity and microsaccades co-vary: alpha lateralisation is stronger in trials with microsaccades toward compared to away from the memorised location of the to-be-attended item and occurs earlier in trials with earlier microsaccades toward this item. Critically, however, trials without attention-driven microsaccades nevertheless showed clear spatial modulation of alpha activity - comparable to the neural modulation observed in trials with attention-driven microsaccades. Thus, directional biases in microsaccades are correlated with neural signatures of covert spatial attention, but they are not a prerequisite for neural modulation by covert spatial attention to be manifest.

The Paradox of Fiction Revisited—Improvised Fictional and Real-Life Social Rejections Evoke Associated and Relatively Similar Psychophysiological Responses

Theatre-based practices, such as improvisation, are frequently applied to simulate everyday social interactions. Although the improvisational context is acknowledged as fictional, realistic emotions may emerge, a phenomenon labelled the ‘paradox of fiction’. This study investigated how manipulating the context (real-life versus fictional) modulates psychophysiological reactivity to social rejection during dyadic interactions. We measured psychophysiological responses elicited during real-life (interview) and fictional (improvisation exercises) social rejections. We analysed the heart rate (HR), skin conductance, facial muscle activity, and electrocortical activity (electroencephalographic (EEG) alpha asymmetry) of student teachers (N = 39) during various social rejections (devaluing, interrupting, nonverbal rejection). All social rejections evoked negative EEG alpha asymmetry, a measure reflecting behavioural withdrawal motivation. Psychophysiological responses during real-life and fictional rejections correlated, and rejection type modified the responses. When comparing responses across all rejection types, facial muscle activity and EEG alpha asymmetry did not differ between real-life and fictional rejections, whereas HR decelerated and skin conductance increased during fictional rejections. These findings demonstrate that regardless of cognitive awareness of fictionality, relatively subtle social rejections elicited psychophysiological reactivity indicating emotional arousal and negative valence. These findings provide novel, biological evidence for the application of theatre-based improvisation to studying experientially everyday social encounters.