Preparatory α-band oscillations reflect spatial gating independently of predictions regarding target identity

Stage-dependent role of interhemispheric pathway for motor recovery in primates

Whether and how the non-lesional sensorimotor cortex is activated and contributes to post-injury motor recovery is controversial. Here, we investigated the role of interhemispheric pathway from the contralesional to ipsilesional premotor cortex in activating the ipsilesional sensorimotor cortex and promoting recovery after lesioning the lateral corticospinal tract at the cervical cord, by unidirectional chemogenetic blockade in macaques. The blockade impaired dexterous hand movements during the early recovery stage. Electrocorticographical recording showed that the low frequency band activity of the ipsilesional premotor cortex around movement onset was decreased by the blockade during the early recovery stage, while it was increased by blockade during the intact state and late recovery stage. These results demonstrate that action of the interhemispheric pathway changed from inhibition to facilitation, to involve the ipsilesional sensorimotor cortex in hand movements during the early recovery stage. The present study offers insights into the stage-dependent role of the interhemispheric pathway and a therapeutic target in the early recovery stage after lesioning of the corticospinal tract.

Distractor inhibition by alpha oscillations is controlled by an indirect mechanism governed by goal-relevant information

The role of alpha oscillations (8-13 Hz) in cognition is intensively investigated. While intracranial animal recordings demonstrate that alpha oscillations are associated with decreased neuronal excitability, it is been questioned whether alpha oscillations are under direct control from frontoparietal areas to suppress visual distractors. We here point to a revised mechanism in which alpha oscillations are controlled by an indirect mechanism governed by the load of goal-relevant information - a view compatible with perceptual load theory. We will outline how this framework can be further tested and discuss the consequences for network dynamics and resource allocation in the working brain.

Attentional modulation of beta-power aligns with the timing of behaviorally relevant rhythmic sounds

It is largely unknown how attention adapts to the timing of acoustic stimuli. To address this, we investigated how hemispheric lateralization of alpha (7-13 Hz) and beta (14-24 Hz) oscillations, reflecting voluntary allocation of auditory spatial attention, is influenced by tempo and predictability of sounds. We recorded electroencephalography while healthy adults listened to rhythmic sound streams with different tempos that were presented dichotically to separate ears, thus permitting manipulation of spatial-temporal attention. Participants responded to stimulus-onset-asynchrony (SOA) deviants (-90 ms) for given tones in the attended rhythm. Rhythm predictability was controlled via the probability of SOA deviants per block. First, the results revealed hemispheric lateralization of beta-power according to attention direction, reflected as ipsilateral enhancement and contralateral suppression, which was amplified in high- relative to low-predictability conditions. Second, fluctuations in the time-resolved beta-lateralization aligned more strongly with the attended than the unattended tempo. Finally, a trend-level association was found between the degree of beta-lateralization and improved ability to distinguish between SOA-deviants in the attended versus unattended ear. Differently from previous studies, we presented continuous rhythms in which task-relevant and irrelevant stimuli had different tempo, thereby demonstrating that temporal alignment of beta-lateralization with attended sounds reflects top-down attention to sound timing.

Global attentional selection of visual features is not associated with selective modulation of posterior alpha-band activity

Attending to a single feature, such as color or motion, leads to global modulation of neural processing associated with the representation of the attended features. Alpha-band modulations are hypothesized to be a marker (and even a mechanism) of the modulation of neural processing. By adopting a previously used attentional shifting paradigm, we examined whether alpha-band dynamics are linked to sustained Feature-Based-Attentional (FBA) selection. For this purpose, we presented task-irrelevant flickering random dot kinematograms (RDKs) in the periphery that either did or did not share the to-be-attended color of centrally presented task-relevant RDKs and should thus be subject to global FBA selection. Steady-state visual evoked potentials (SSVEPs) and alpha-band activity associated with these task-irrelevant RDKs were analyzed to quantify FBA modulation. Overall, the SSVEP results replicated previous findings: relative to a pre-cue baseline, SSVEP amplitudes for peripheral RDKs were significantly enhanced when these RDKs shared the to-be-attended color of the central RDKs and were not modulated when they shared the centrally to-be-ignored color. Nevertheless, there were no differences in alpha-band amplitude modulations between signals recorded contralateral to the RDKs sharing the centrally attended color and RDKs sharing the centrally ignored color. Hence, alpha-band modulations seem not to index the sustained global selection of attended over unattended feature values within the same feature dimension.

Task prioritization modulates alpha, theta and beta EEG dynamics reflecting proactive cognitive control

Most neuroscientific studies investigating mental effort apply unspecific effort allocation paradigms. In contrast, the present EEG study targets specific effort allocation during task prioritization. Twenty-eight participants performed a cued number classification task during the retention interval of a working memory task including retrospective cues. One of two possible number classifications was done per trial. Each trial started with a cue indicating which of the two tasks would be more important in the upcoming trial. Subjects were told to engage in both tasks, but to concentrate on the important one. Feedback given at the end of each trial was calculated based on task performance, with scores obtained from the relevant task being tripled. Participants performed significantly better in either task when it was important compared to when not. Task prioritization modulates theta, alpha and beta oscillations, predominantly during task preparation. Multivariate pattern analysis revealed that the exact type of the two possible number classifications was decodable, however, decoding accuracy did not depend on task importance. Hemispheric alpha power asymmetries indicating attentional orienting between working memory representations also did not depend on task importance. The findings suggest that task prioritization primarily affects proactive cognitive control on a superordinate level.

Expectance of low contrast retro-cues does not modulate anticipatory alpha power

It has been proposed that alpha oscillations reflect the endogenous modulation of visual cortex excitability. In particular, alpha power increases during the maintenance period in Working Memory (WM) tasks have been interpreted as a mechanism to avoid potential interference of incoming stimuli. In this study we tested whether alpha power was modulated during the maintenance of WM to enhance the processing of relevant incoming perceptual stimuli. To this aim, we manipulated the contrast of a stimulus presented during the maintenance period of a WM task. The to-be-detected stimulus could indicate which of the encoded representations was going to be probed after the delay (spatial retro-cue) or could signal that all the representations had equal probability to be tested (neutral retro-cue). Time-frequency analysis revealed that alpha power preceding retro-cue presentation was not differently modulated by the two different contrast conditions. This is, participants did not endogenously modulate alpha oscillations upon low perceptual contrast stimuli incoming. These results suggest that alpha delay activity is not a goal directed mechanism to control the inflow of information during WM maintenance. Instead, current data suggest that alpha delayed activity might be an index of increased allocation of attentional resources to the processing of the WM representations.

Activity in the Fronto-Parietal and Visual Cortex Is Modulated by Feature-Based Attentional Weighting

In day-to-day dynamic activities where sensory input is abundant, stimulus representations in the visual cortex are modulated based on their attentional priority. Several studies have established the top-down role of a fronto-parietal dorsal attention network in selective attention. In the current study, we aimed to investigate whether activity of subregions of this network and the visual cortex is modulated by feature-based attentional weighting, and if so, whether their timecourses of activity are correlated. To this end, we analyzed fMRI data of 28 healthy subjects, who performed a feature-based go/no-go task. Participants had to attend to one or two colored streams of sinusoidal gratings and respond to each grating in the task-relevant stream(s) except to a single non-target grating. Univariate and multivariate fMRI results indicated that activity in bilateral fronto-parietal (frontal eye fields, intraparietal sulcus and superior parietal lobe) and visual (V1-V4, lateral occipital cortex and fusiform gyrus) regions was modulated by selecting one instead of attending to two gratings. Functional connectivity was not significantly different between fronto-parietal and visual regions when attending to one as opposed to two gratings. Our study demonstrates that activity in subregions of both the fronto-parietal and visual cortex is modified by feature-based attentional weighting.

Alpha suppression indexes a spotlight of visual-spatial attention that can shine on both perceptual and memory representations

Although researchers have been recording the human electroencephalogram (EEG) for almost a century, we still do not completely understand what cognitive processes are measured by the activity of different frequency bands. The 8- to 12-Hz activity in the alpha band has long been a focus of this research, but our understanding of its links to cognitive mechanisms has been rapidly evolving recently. Here, we review and discuss the existing evidence for two competing perspectives about alpha activity. One view proposes that the suppression of alpha-band power following the onset of a stimulus array measures attentional selection. The competing view is that this same activity measures the buffering of the task-relevant representations in working memory. We conclude that alpha-band activity following the presentation of stimuli appears to be due to the operation of an attentional selection mechanism, with characteristics that mirror the classic views of attention as selecting both perceptual inputs and representations already stored in memory.

Pre-stimulus alpha predicts inattentional blindness

Pre- and post-stimulus oscillatory activity between 8 and 12 hertz, referred to as the alpha-band, correlates with conscious visual awareness of stimuli across a variety of psychophysical tasks. Within an EEG-adapted inattentional blindness task, the current study sought to examine whether this relationship holds for conscious awareness of stimuli under conditions of inattentional blindness. Noticing rates of the task-irrelevant unexpected stimulus were correlated with a significant decrease in alpha power over bilateral parietal-occipital areas during the pre-stimulus interval, and a significant decrease in alpha power over parietal-occipital regions in the right hemisphere during the post-stimulus interval. Findings are taken to imply alpha-band neural activity represents a valid correlate of consciousness that is not confounded by task relevancy or the need for report.

Inefficient resource allocation is associated with reduced alpha activity in parietal regions in individuals with Parkinson's disease

The brain's ability to act as an input filter and to suppress actions is crucial to navigate everyday life and impairments in these abilities affect quality of life substantially. Although Parkinson's disease (PD) is primarily known as a movement disorder, recent research has redefined it as a multisystem disorder affecting cognition, in particular inhibitory control and attentional resource allocation. Analysing the neural mechanisms underlying this cognitive deficit provides a better understanding of brain changes observed in patients affected by PD. Therefore, this study aimed to identify resource allocation to relevant and irrelevant stimuli in patients affected by PD. Besides neuropsychological tests, we employed electroencephalographic recordings during an auditory oddball paradigm in 13 patients suffering from idiopathic PD and 11 healthy controls (HC). Participants were instructed to ignore the standard stimulus and to respond as fast as possible to the rarely presented target tone. Event-related potentials (ERP) and time-frequency representations (TFR) were analyzed. Patients affected by PD showed faster response latencies to the task-irrelevant standard tones, but slower response latencies to target tones compared to HC. This observation was prominent at frontal sites during later P3-like processing stages. Reaction time, however, was prolonged in patients with PD, suggesting inefficient resource allocation. Additionally, TFR revealed reduced parietal alpha activity, which is associated with distractor suppression and functional inhibition in patients with PD compared to healthy controls. Thus, our results point towards inefficient resource allocation in patients with PD possibly driven by less functional inhibition through parietal alpha activity.

Proactive Control of Emotional Distraction: Evidence From EEG Alpha Suppression

Biased attention towards emotional stimuli is adaptive, as it facilitates responses to important threats and rewards. An unfortunate consequence is that emotional stimuli can become potent distractors when they are irrelevant to current goals. How can this distraction be overcome despite the bias to attend to emotional stimuli? Recent studies show that distraction by irrelevant flankers is reduced when distractor frequency is high, even if they are emotional. A parsimonious explanation is that the expectation of frequent distractors promotes the use of proactive control, whereby attentional control settings can be altered to minimize distraction before it occurs. It is difficult, however, to infer proactive control on the basis of behavioral data alone. We therefore measured neural indices of proactive control while participants performed a target-detection task in which irrelevant peripheral distractors (either emotional or neutral) could appear either frequently (on 75% of trials) or rarely (on 25% of trials). We measured alpha power during the pre-stimulus period to assess proactive control and during the post-stimulus period to determine the consequences of control for subsequent processing. Pre-stimulus alpha power was tonically suppressed in the high, compared to low, distractor frequency condition, regardless of expected distractor valence, indicating sustained use of proactive control. In contrast, post-stimulus alpha suppression was reduced in the high-frequency condition, suggesting that proactive control reduced the need for post-stimulus adjustments. Our findings indicate that a sustained proactive control strategy accounts for the reduction in both emotional and non-emotional distraction when distractors are expected to appear frequently.

One Thing Leads to Another: Anticipating Visual Object Identity Based on Associative-Memory Templates

Probabilistic associations between stimuli afford memory templates that guide perception through proactive anticipatory mechanisms. A great deal of work has examined the behavioral consequences and human electrophysiological substrates of anticipation following probabilistic memory cues that carry spatial or temporal information to guide perception. However, less is understood about the electrophysiological substrates linked to anticipating the sensory content of events based on recurring associations between successive events. Here, we demonstrate behavioral and electrophysiological signatures of using associative-memory templates to guide perception, while equating spatial and temporal anticipation (experiments 1 and 2), as well as target probability and response demands (experiment 2). By recording the electroencephalogram in the two experiments (N = 55; 24 females), we show that two markers in human electrophysiology implicated in spatial and temporal anticipation also contribute to the anticipation of perceptual identity, as follows: attenuation of alpha-band oscillations and the contingent negative variation (CNV). Together, our results show that memory-guided identity templates proactively impact perception and are associated with anticipatory states of attenuated alpha oscillations and the CNV. Furthermore, by isolating object-identity anticipation from spatial and temporal anticipation, our results suggest a role for alpha attenuation and the CNV in specific visual content anticipation beyond general changes in neural excitability or readiness.SIGNIFICANCE STATEMENT Probabilistic associations between stimuli afford memory templates that guide perception through proactive anticipatory mechanisms. The current work isolates the behavioral benefits and electrophysiological signatures of memory-guided identity-based anticipation, while equating anticipation of space, time, motor responses, and task relevance. Our results show that anticipation of the specific identity of a forthcoming percept impacts performance and is associated with states of attenuated alpha oscillations and the contingent negative variation, extending previous work implicating these neural substrates in spatial and temporal preparatory attention. Together, this work bridges fields of attention, memory, and perception, providing new insights into the neural mechanisms that support complex attentional templates.

Unraveling the Relation between EEG Correlates of Attentional Orienting and Sound Localization Performance: A Diffusion Model Approach

Understanding the contribution of cognitive processes and their underlying neurophysiological signals to behavioral phenomena has been a key objective in recent neuroscience research. Using a diffusion model framework, we investigated to what extent well-established correlates of spatial attention in the electroencephalogram contribute to behavioral performance in an auditory free-field sound localization task. Younger and older participants were instructed to indicate the horizontal position of a predefined target among three simultaneously presented distractors. The central question of interest was whether posterior alpha lateralization and amplitudes of the anterior contralateral N2 subcomponent (N2ac) predict sound localization performance (accuracy, mean RT) and/or diffusion model parameters (drift rate, boundary separation, non-decision time). Two age groups were compared to explore whether, in older adults (who struggle with multispeaker environments), the brain-behavior relationship would differ from younger adults. Regression analyses revealed that N2ac amplitudes predicted drift rate and accuracy, whereas alpha lateralization was not related to behavioral or diffusion modeling parameters. This was true irrespective of age. The results indicate that a more efficient attentional filtering and selection of information within an auditory scene, reflected by increased N2ac amplitudes, was associated with a higher speed of information uptake (drift rate) and better localization performance (accuracy), while the underlying response criteria (threshold separation), mean RTs, and non-decisional processes remained unaffected. The lack of a behavioral correlate of poststimulus alpha power lateralization constrasts with the well-established notion that prestimulus alpha power reflects a functionally relevant attentional mechanism. This highlights the importance of distinguishing anticipatory from poststimulus alpha power modulations.

Dynamic causal modelling of phase-amplitude interactions

Models of coupled phase oscillators are used to describe a wide variety of phenomena in neuroimaging. These models typically rest on the premise that oscillator dynamics do not evolve beyond their respective limit cycles, and hence that interactions can be described purely in terms of phase differences. Whilst mathematically convenient, the restrictive nature of phase-only models can limit their explanatory power. We therefore propose a generalisation of dynamic causal modelling that incorporates both phase and amplitude. This allows for the separate quantifications of phase and amplitude contributions to the connectivity between neural regions. We show, using model-generated data and simulations of coupled pendula, that phase-amplitude models can describe strongly coupled systems more effectively than their phase-only counterparts. We relate our findings to four metrics commonly used in neuroimaging: the Kuramoto order parameter, cross-correlation, phase-lag index, and spectral entropy. We find that, with the exception of spectral entropy, the phase-amplitude model is able to capture all metrics more effectively than the phase-only model. We then demonstrate, using local field potential recordings in rodents and functional magnetic resonance imaging in macaque monkeys, that amplitudes in oscillator models play an important role in describing neural dynamics in anaesthetised brain states.

Oscillatory Control over Representational States in Working Memory

In the visual world, attention is guided by perceptual goals activated in visual working memory (VWM). However, planning multiple-task sequences also requires VWM to store representations for future goals. These future goals need to be prevented from interfering with the current perceptual task. Recent findings have implicated neural oscillations as a control mechanism serving the implementation and switching of different states of prioritization of VWM representations. We review recent evidence that posterior alpha-band oscillations underlie the flexible activation and deactivation of VWM representations and that frontal delta-to-theta-band oscillations play a role in the executive control of this process. That is, frontal delta-to-theta appears to orchestrate posterior alpha through long-range oscillatory networks to flexibly set up and change VWM states during multitask sequences.

Role of the dorsal attention network in distracter suppression based on features

Selective attention allows us to prioritize the processing of relevant information and filter out irrelevant information. Human functional neuroimaging and lesion-based studies have highlighted the fronto-parietal dorsal attention network (DAN) as an important network in this process. In this study, we investigated the role of the DAN in distracter suppression by dynamically modifying the priority of visual information (target > high priority distracter > low priority distracter) based on features only. To this end, we collected fMRI data in 24 healthy subjects, who performed a feature-based variant of the sustained attention to response task. Participants had to select one or attend two stream(s) of overlapping digits that differed in color and respond to each digit in the task-relevant stream(s) except to a single non-target digit. Results showed higher DAN activity when a target was co-presented with a high versus low priority distracter. Furthermore, higher DAN activity was observed when selectively attending one (target + high/low priority distracter) versus simultaneously attending two (target + target) stream(s) of digits. In conclusion, our study highlights the contribution of the DAN in the feature-based suppression of task-irrelevant information.

Neural correlates of cue predictiveness during intentional and incidental associative learning: A time-frequency study

Incidental learning allows us to extract statistical relations between events in our daily lives without the intention to learn them. Whereas anticipation during intentional associative learning has been linked to increased and decreased theta band activity, comparatively little research has focused on incidental learning. The study of such a pervasive mechanism of incidental learning faces the challenge of finding an appropriate paradigm. Similarly, while posterior alpha band activity has been shown to facilitate attention to a predictable target location, it is not clear whether alpha power could mediate attention given other predictive information; e.g., when the only available information provided by the cue is the likelihood of the target outcome. Here we used a stimulus-stimulus associative learning task to investigate whether a cue carries information on its contingent relationship with a target outcome, not only when their relationship is learned intentionally but also when it could be learned incidentally. Moreover, by presenting the target outcome in a visual search task, we were also able to study whether anticipatory attention can be modulated by the intentional or the incidental knowledge of the likelihood of a target outcome given a predictive (or non-predictive) cue. Participants were exposed to streams of cue-target outcome trials, where one of two possible cues and one of two possible outcomes were displayed. Intention to learn was manipulated by asking participants to assess whether one of the target outcomes (the intentional one) was more likely to appear following one of the cues (the intentional one). Any learning regarding the other cue-outcome relationship would be incidental. We found that frontal and temporal theta band activity were sensitive to the predictive value of a cue (predictive cues elicited lower theta power). Moreover, left temporal theta was sensitive to the intention to learn associations (theta activity elicited by intentional learning cues was higher). Alpha power, by contrast, was not modulated by cue predictiveness of the target outcome. These findings suggest that theta band activity carries information about the predictive value of a cue. The topographical differences between theta for intentional and incidental learning suggest distinct cortical networks activated depending on whether the relationship between a cue and an outcome has been learned intentionally or incidentally.

The emergence of synchrony in networks of mutually inferring neurons

This paper considers the emergence of a generalised synchrony in ensembles of coupled self-organising systems, such as neurons. We start from the premise that any self-organising system complies with the free energy principle, in virtue of placing an upper bound on its entropy. Crucially, the free energy principle allows one to interpret biological systems as inferring the state of their environment or external milieu. An emergent property of this inference is synchronisation among an ensemble of systems that infer each other. Here, we investigate the implications of neuronal dynamics by simulating neuronal networks, where each neuron minimises its free energy. We cast the ensuing ensemble dynamics in terms of inference and show that cardinal behaviours of neuronal networks - both in vivo and in vitro - can be explained by this framework. In particular, we test the hypotheses that (i) generalised synchrony is an emergent property of free energy minimisation; thereby explaining synchronisation in the resting brain: (ii) desynchronisation is induced by exogenous input; thereby explaining event-related desynchronisation and (iii) structure learning emerges in response to causal structure in exogenous input; thereby explaining functional segregation in real neuronal systems.

The possibility to make choices modulates feature-based effects of reward

When making decisions, humans can maximize the positive outcome of their actions by choosing the option associated with the highest reward. We have recently shown that choices modulate effects of reward via a bias in spatial attention: Locations associated with a lower reward are anticipatorily suppressed, as indicated by delayed responses to low-reward targets and increased parieto-occipital alpha power. Here, we investigated whether this inhibition also occurs when reward is not coupled to location but to a nonspatial feature (color). We analyzed reaction times to single targets associated with a low or high reward as a function of whether a second trial type, choice-trials, were interleaved. In choice-trials, participants could choose either one of two targets to obtain the associated reward. Indeed, responses to low-reward targets were slower when choice-trials were present, magnifying the influence of reward, and this delay was more pronounced in trials immediately following a choice. No corresponding changes in parieto-occipital alpha power were observed, but the behavioral findings suggest that choices modulate a reward-related bias in feature-based attention in a similar manner as for spatial attention, and support the idea that reward primarily affects behaviour when it is of immediate relevance.

Priority Switches in Visual Working Memory are Supported by Frontal Delta and Posterior Alpha Interactions

Visual working memory (VWM) distinguishes between representations relevant for imminent versus future perceptual goals. We investigated how the brain sequentially prioritizes visual working memory representations that serve consecutive tasks. Observers remembered two targets for a sequence of two visual search tasks, thus making one target currently relevant, and the other prospectively relevant. We show that during the retention interval prior to the first search, lateralized parieto-occipital EEG alpha (8-14 Hz) suppression is stronger for current compared with prospective search targets. Crucially, between the first and second search task, this difference in posterior alpha lateralization reverses, reflecting the change in priority states of the two target representations. Connectivity analyses indicate that this switch in posterior alpha lateralization is driven by frontal delta/low-theta (2-6 Hz) activity. Moreover, this frontal low-frequency signal also predicts task performance after the switch. We thus obtained evidence for large-scale network interactions underlying the flexible shifting between the priority states of multiple memory representations in VWM.

Enhanced spatial focusing increases feature-based selection in unattended locations

Attention is a multifaceted phenomenon, which operates on features (e.g., colour or motion) and over space. A fundamental question is whether the attentional selection of features is confined to the spatially-attended location or operates independently across the entire visual field (global feature-based attention, GFBA). Studies providing evidence for GFBA often employ feature probes presented at spatially unattended locations, which elicit enhanced brain responses when they match a currently-attended target feature. However, the validity of this interpretation relies on consistent spatial focusing onto the target. If the probe were to temporarily attract spatial attention, the reported effects could reflect transient spatial selection processes, rather than GFBA. Here, using magnetoencephalographic recordings (MEG) in humans, we manipulate the strength and consistency of spatial focusing to the target by increasing the target discrimination difficulty (Experiment 1), and by demarcating the upcoming target’s location with a placeholder (Experiment 2), to see if GFBA effects are preserved. We observe that motivating stronger spatial focusing to the target did not diminish the effects of GFBA. Instead, aiding spatial pre-focusing with a placeholder enhanced the feature response at unattended locations. Our findings confirm that feature selection effects measured with spatially-unattended probes reflect a true location-independent neural bias.