The functional significance of theta and upper alpha oscillations

Recent findings are reviewed indicating that upper alpha oscillations - when analyzed with appropriate time/ frequency resolution - show a similar physiological reactivity as theta in working memory tasks. Comparable to theta, a load dependent increase in power can be observed during retention and increased evoked activity during retrieval. During retrieval attempts theta behaves like a traveling wave spreading from anterior to posterior sites. During actual retrieval, however, evoked upper alpha becomes transiently nested in theta. We suggest that theta reflects working memory functions whereas upper alpha may be important for the reactivation of long-term memory codes in short-term memory.     

Electrophysiological spatiotemporal dynamics during implicit visual threat processing

Numerous studies have found evidence for corticolimbic theta band electroencephalographic (EEG) oscillations in the neural processing of visual stimuli perceived as threatening. However, varying temporal and topographical patterns have emerged, possibly due to varying arousal levels of the stimuli. In addition, recent studies suggest neural oscillations in delta, theta, alpha, and beta-band frequencies play a functional role in information processing in the brain. This study implemented a data-driven PCA based analysis investigating the spatiotemporal dynamics of electroencephalographic delta, theta, alpha, and beta-band frequencies during an implicit visual threat processing task. While controlling for the arousal dimension (the intensity of emotional activation), we found several spatial and temporal differences for threatening compared to nonthreatening visual images. We detected an early posterior increase in theta power followed by a later frontal increase in theta power, greatest for the threatening condition. There was also a consistent left lateralized beta desynchronization for the threatening condition. Our results provide support for a dynamic corticolimbic network, with theta and beta band activity indexing processes pivotal in visual threat processing.     

Theta synchronizes the activity of medial prefrontal neurons during learning

Memory consolidation is thought to involve the gradual transfer of transient hippocampal-dependent traces to distributed neocortical sites via the rhinal cortices. Recently, medial prefrontal (mPFC) neurons were shown to facilitate this process when their activity becomes synchronized. However, the mechanisms underlying this enhanced synchrony remain unclear. Because the hippocampus projects to the mPFC, we tested whether theta oscillations contribute to synchronize mPFC neurons during learning. Thus, we obtained field (LFP) and unit recordings from multiple mPFC sites during the acquisition of a trace-conditioning task, where a visual conditioned stimulus (CS) predicted reward delivery. In quiet waking, the activity of mPFC neurons was modulated by theta oscillations. During conditioning, CS presentation caused an increase in mPFC theta power that augmented as the CS gained predictive value for reward delivery. This increased theta power coincided with a transient theta phase locking at distributed mPFC sites, an effect that was also manifest in the timing of mPFC unit activity. Overall, these results show that theta oscillations contribute to synchronize neuronal activity at distributed mPFC sites, suggesting that the hippocampus, by generating a stronger theta source during learning, can synchronize mPFC activity, in turn facilitating rhinal transfer of its activity to the neocortex.     

Conscious, preconscious, and subliminal processing: a testable taxonomy

Of the many brain events evoked by a visual stimulus, which are specifically associated with conscious perception, and which merely reflect non-conscious processing? Several recent neuroimaging studies have contrasted conscious and non-conscious visual processing, but their results appear inconsistent. Some support a correlation of conscious perception with early occipital events, others with late parieto-frontal activity. Here we attempt to make sense of these dissenting results. On the basis of the global neuronal workspace hypothesis, we propose a taxonomy that distinguishes between vigilance and access to conscious report, as well as between subliminal, preconscious and conscious processing. We suggest that these distinctions map onto different neural mechanisms, and that conscious perception is systematically associated with surges of parieto-frontal activity causing top-down amplification.     

Shadows of music-language interaction on low frequency brain oscillatory patterns

Electrophysiological studies investigating similarities between music and language perception have relied exclusively on the signal averaging technique, which does not adequately represent oscillatory aspects of electrical brain activity that are relevant for higher cognition. The current study investigated the patterns of brain oscillations during simultaneous processing of music and language using visually presented sentences and auditorily presented chord sequences. Music-syntactically regular or irregular chord functions were presented in sync with syntactically or semantically correct or incorrect words. Irregular chord functions (presented simultaneously with a syntactically correct word) produced an early (150-250 ms) spectral power decrease over anterior frontal regions in the theta band (5-7 Hz) and a late (350-700 ms) power increase in both the delta and the theta band (2-7 Hz) over parietal regions. Syntactically incorrect words (presented simultaneously with a regular chord) elicited a similar late power increase in delta-theta band over parietal sites, but no early effect. Interestingly, the late effect was significantly diminished when the language-syntactic and music-syntactic irregularities occurred at the same time. Further, the presence of a semantic violation occurring simultaneously with regular chords produced a significant increase in later delta-theta power at posterior regions; this effect was marginally decreased when the identical semantic violation occurred simultaneously with a music syntactical violation. Altogether, these results show that low frequency oscillatory networks get activated during the syntactic processing of both music and language, and further, these networks may possibly be shared.     

情绪面孔的意识神经相关物及其无意识自动加工：来自事件相关电位的证据

意识的神经相关物尚有争议, 且个体能否无意识自动检测视觉环境变化尚不清楚。本研究采用非注意视盲范式操控视觉意识, 并引入具有社会信息的情绪面孔, 探讨意识的神经相关物以及视觉意识与自动检测变化机制的关系。在A阶段, 部分被试对任务无关的情绪面孔处于无意识水平; 在B阶段, 所有被试对任务无关的情绪面孔处于意识水平; 在C阶段, 所有被试对任务相关的情绪面孔处于意识水平。结果显示, 任务无关的情绪面孔的意识过程诱发视觉意识负波(visual awareness negativity, VAN)、晚期正成分(late positivity, LP)和晚期枕区正成分(late occipital positivity, LOP)。此外, 无意识的情绪面孔能诱发视觉失匹配负波(visual mismatch negativity, vMMN), 且其幅值不受意识影响, 但是受任务相关性调制。这些结果提示对情绪面孔的视觉意识在不同的时间进程上有不同的ERP指标——VAN反映早期知觉经验, 而LP和LOP反映晚期意识过程, 而且面孔情绪信息的自动加工独立于视觉意识, 但是受视觉注意调制。     

Toward ecologically realistic theories in visual short-term memory research

Recent evidence from neuroimaging and psychophysics suggests common neural and representational substrates for visual perception and visual short-term memory (VSTM). Visual perception is adapted to a rich set of statistical regularities present in the natural visual environment. Common neural and representational substrates for visual perception and VSTM suggest that VSTM is adapted to these same statistical regularities too. This article discusses how the study of VSTM can be extended to stimuli that are ecologically more realistic than those commonly used in standard VSTM experiments and what the implications of such an extension could be for our current view of VSTM. We advocate for the development of unified models of visual perception and VSTM—probabilistic and hierarchical in nature—incorporating prior knowledge of natural scene statistics.     

Theta oscillations predict the detrimental effects of memory retrieval

Retrieving a target item from episodic memory typically enhances later memory for the retrieved item but causes forgetting of competing irrelevant memories. This finding is termed retrieval-induced forgetting (RIF) and is assumed to be the consequence of an inhibitory mechanism resolving retrieval competition. In the present study, we examined brain oscillatory processes related to RIF, as induced by competitive memory retrieval. Contrasting a competitive with a noncompetitive retrieval condition, we found a stronger increase in early evoked theta (4–7 Hz) activity, which specifically predicted RIF, but not retrieval-induced enhancement. Within the cognitive framework of RIF, these findings suggest that theta oscillations reflect arising interference and its resolution during competitive retrieval in episodic memory. Supplemental materials for this article may be downloaded from http://cabn.psychonomic-journals.org/content/supplemental.     

Brain oscillatory activity associated with task switching and feedback processing

In this study, we sought to dissociate event-related potentials (ERPs) and the oscillatory activity associated with signals indicating feedback about performance (outcome-based behavioral adjustment) and the signals indicating the need to change or maintain a task set (rule-based behavioral adjustment). With this purpose in mind, we noninvasively recorded electroencephalographic signals, using a modified version of the Wisconsin card sorting task, in which feedback processing and task switching could be studied separately. A similar late positive component was observed for the switch and correct feedback signals on the first trials of a series, but feedback-related negativity was observed only for incorrect feedback. Moreover, whereas theta power showed a significant increase after a switch cue and after the first positive feedback of a new series, a selective frontal beta–gamma increase was observed exclusively in the first positive feedback (i.e., after the selection of the new rule). Importantly, for the switch cue, beta–alpha activity was suppressed rather than increased. This clear dissociation between the cue and feedback stimuli in task switching emphasizes the need to accurately study brain oscillatory activity to disentangle the role of different cognitive control processes.     

Longitudinal study of perception of structured optic flow and random visual motion in infants using high‐density EEG

Electroencephalogram (EEG) was used in infants at 3–4 months and 11–12 months to longitudinally study brain electrical activity as the infants were exposed to structured forwards and reversed optic flow, and non‐structured random visual motion. Analyses of visual evoked potential (VEP) and temporal spectral evolution (TSE, time‐dependent amplitude changes) were performed on EEG data recorded with a 128‐channel sensor array. VEP results showed infants to significantly differentiate between the radial motion conditions, but only at 11–12 months where they showed shortest latency for forwards optic flow and longest latency for random visual motion. When the TSE results of the motion conditions were compared with those of a static non‐flow dot pattern, infants at 3–4 and 11–12 months both showed significant differences in induced activity. A decrease in amplitudes at 5–7 Hz was observed as desynchronized theta‐band activity at both 3–4 and 11–12 months, while an increase in amplitudes at 9–13 Hz was observed as synchronized alpha‐band activity only at 11–12 months. It was concluded that brain electrical activities related to visual motion perception change during the first year of life, and these changes can be observed both in the VEP and induced activities of EEG. With adequate neurobiological development and locomotor experience infants around 1 year of age rely, more so than when they were younger, on structured optic flow and show a more adult‐like specialization for motion where faster oscillating cell assemblies have fewer but more specialized neurons, resulting in improved visual motion perception.     

Oscillatory brain responses evoked by video game events: the case of super monkey ball 2.

Electroencephalography (EEG) was recorded while the subjects played a video game where the player had to steer a monkey into a goal while collecting bananas for extra points and had to avoid falling off the edge of the game board. Each of these three studied events evoked differential EEG oscillatory changes. Picking up bananas evoked decreased theta activation on central electrodes, decreased high alpha activation on frontal electrodes, and increased beta activation on frontal electrodes. Falling off the game board evoked decreased central theta activation and increased fronto-central beta activation. Reaching the goal evoked increased theta activation on parietal electrodes, increased low alpha activation on frontal electrodes, increased high alpha activation on frontal, central, and parietal electrodes, and increased beta activation on frontal and central electrodes. It is suggested that the EEG oscillations evoked by picking up bananas reflect increased cortical activation and arousal; the oscillations evoked by falling off the edge of the game board reflect motor functions; and the oscillations evoked by reaching the goal reflect a relaxed state. Thus, EEG may turn out to be a valuable tool when examining psychological responses to video game events.     

Action goal selection and motor planning can be dissociated by tool use

The preparation of eye or hand movements enhances visual perception at the upcoming movement end position. The spatial location of this influence of action on perception could be determined either by goal selection or by motor planning. We employed a tool use task to dissociate these two alternatives. The instructed goal location was a visual target to which participants pointed with the tip of a triangular hand-held tool. The motor endpoint was defined by the final fingertip position necessary to bring the tool tip onto the goal. We tested perceptual performance at both locations (tool tip endpoint, motor endpoint) with a visual discrimination task. Discrimination performance was enhanced in parallel at both spatial locations, but not at nearby and intermediate locations, suggesting that both action goal selection and motor planning contribute to visual perception. In addition, our results challenge the widely held view that tools extend the body schema and suggest instead that tool use enhances perception at those precise locations which are most relevant during tool action: the body part used to manipulate the tool, and the active tool tip.     

Neural correlates of object indeterminacy in art compositions

Indeterminate art invokes a perceptual dilemma in which apparently detailed and vivid images resist identification. We used event-related fMRI to study visual perception of representational, indeterminate and abstract paintings. We hypothesized increased activation along a gradient of posterior-to-anterior ventral visual areas with increased object resolution, and postulated that object resolution would be associated with visual imagery. Behaviorally, subjects were faster to recognize familiar objects in representational than in both indeterminate and abstract paintings. We found activation within a distributed cortical network that includes visual, parietal, limbic and prefrontal regions. Representational paintings, which depict scenes cluttered with familiar objects, evoked stronger activation than indeterminate and abstract paintings in higher-tier visual areas. Perception of scrambled paintings was associated with imagery-related activation in the precuneus and prefrontal cortex. Finally, representational paintings evoked stronger activation than indeterminate paintings in the temporoparietal junction. Our results suggest that perception of familiar content in art works is mediated by object recognition, memory recall and mental imagery, cognitive processes that evoke activation within a distributed cortical network.     

Increased arithmetic complexity is associated with domain-general but not domain-specific magnitude processing in children: A simultaneous fNIRS-EEG study

The investigation of the neural underpinnings of increased arithmetic complexity in children is essential for developing educational and therapeutic approaches and might provide novel measures to assess the effects of interventions. Although a few studies in adults and children have revealed the activation of bilateral brain regions during more complex calculations, little is known about children. We investigated 24 children undergoing one-digit and two-digit multiplication tasks while simultaneously recording functional near-infrared spectroscopy (fNIRS) and electroencephalography (EEG) data. FNIRS data indicated that one-digit multiplication was associated with brain activity in the left superior parietal lobule (SPL) and intraparietal sulcus (IPS) extending to the left motor area, and two-digit multiplication was associated with activity in bilateral SPL, IPS, middle frontal gyrus (MFG), left inferior parietal lobule (IPL), and motor areas. Oscillatory EEG data indicated theta increase and alpha decrease in parieto-occipital sites for both one-digit and two-digit multiplication. The contrast of two-digit versus one-digit multiplication yielded greater activity in right MFG and greater theta increase in frontocentral sites. Activation in frontal areas and theta band data jointly indicate additional domain-general cognitive control and working memory demands for heightened arithmetic complexity in children. The similarity in parietal activation between conditions suggests that children rely on domain-specific magnitude processing not only for two-digit but—in contrast to adults—also for one-digit multiplication problem solving. We conclude that in children, increased arithmetic complexity tested in an ecologically valid setting is associated with domain-general processes but not with alteration of domain-specific magnitude processing.     

Attention and consciousness: related yet different

A recent perceptual imaging experiment uses a rare 2×2 design to dissociate selective visual attention from visual consciousness. Its conclusions support the hypothesis that visual consciousness does not arise from neurons in primary visual cortex and forces a reinterpretation of numerous prior studies.     

Visual perception of markings

Markings, such as designs, writings, diagrams, and depictions, are expressive and communicative human artifacts. The conventional assumption that findings from the study of the visual perception of markings—in particular, of pictures—can be generalized to real-world perception is examined and found to be false. The processes involved in the visual perception of the world and in the visual perception of markings differ in significant ways, and generalizations from one to the other must be undertaken with caution. The visual perception of markings is an identifiable and separate area of study. Implications for a general theory of the perception of markings are examined, and the perception of markings is contrasted with real-world perception.     

Synchronous neural oscillations and cognitive processes

The central problem for cognitive neuroscience is to describe how cognitive processes arise from brain processes. This review summarizes the recent evidence that synchronous neural oscillations reveal much about the origin and nature of cognitive processes such as memory, attention and consciousness. Memory processes are most closely related to theta and gamma rhythms, whereas attention seems closely associated with alpha and gamma rhythms. Conscious awareness may arise from synchronous neural oscillations occurring globally throughout the brain rather than from the locally synchronous oscillations that occur when a sensory area encodes a stimulus. These associations between the dynamics of the brain and cognitive processes indicate progress towards a unified theory of brain and cognition.     

刺激前alpha振荡对视知觉的影响

人类对感觉阈限附近的视觉刺激的知觉不总是一致的。为探究这种视知觉不一致的现象及其神经机制, 一些研究者关注刺激前脑内自发alpha神经振荡(8~13 Hz)对视知觉的影响。近年来的研究发现, 刺激前alpha振荡能量的降低能提高被试的探测击中率, 但不能提高知觉精确度; 而刺激前alpha振荡的相位能预测被试能否成功探测刺激。刺激前alpha能量被认为调控了视皮层的基础活动强度; alpha能量的降低反映了皮层基础活动的增强, 进而提高了对较弱刺激的探测率。刺激前alpha相位则被认为调控了皮层兴奋和抑制的时间; 大脑在刺激呈现时的不同状态(兴奋/抑制)决定了最终的知觉结果。     

Does cross‐frequency phase coupling of oscillatory brain activity contribute to a better understanding of visual working memory?

Nesting of fast rhythmical brain activity (gamma) into slower brain waves (theta) has frequently been suggested as a core mechanism of multi‐item working memory (WM) retention. It provides a better understanding of WM capacity limitations, and, as we discuss in this review article, it can lead to applications for modulating memory capacity. However, could cross‐frequency coupling of brain oscillations also constructively contribute to a better understanding of the neuronal signatures of working memory compatible with theoretical approaches that assume flexible capacity limits? Could a theta‐gamma code also be considered as a neural mechanism of flexible sharing of cognitive resources between memory representations in multi‐item WM? Here, we propose potential variants of theta‐gamma coupling that could explain WM retention beyond a fixed memory capacity limit of a few visual items. Moreover, we suggest how to empirically test these predictions in the future.