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.     

Coordination dynamics of the horse-rider system

The authors studied the interaction between rider and horse by measuring their ensemble motions in a trot sequence, comparing 1 expert and 1 novice rider. Whereas the novice's movements displayed transient departures from phase synchrony, the expert's motions were continuously phase-matched with those of the horse. The tight ensemble synchrony between the expert and the horse was accompanied by an increase in the temporal regularity of the oscillations of the trunk of the horse. Observed differences between expert and novice riders indicated that phase synchronization is by no means perfect but requires extended practice. Points of contact between horse and rider may haptically convey effective communication between them.     

Synchrony and the social tuning of compassion

Although evidence has suggested that synchronized movement can foster cooperation, the ability of synchrony to increase costly altruism and to operate as a function of emotional mechanisms remains unexplored. We predicted that synchrony, due to an ability to elicit low-level appraisals of similarity, would enhance a basic compassionate response toward victims of moral transgressions and thereby increase subsequent costly helping behavior on their behalf. Using a manipulation of rhythmic synchrony, we show that synchronous others are not only perceived to be more similar to oneself but also evoke more compassion and altruistic behavior than asynchronous others experiencing the same plight. These findings both support the view that a primary function of synchrony is to mark others as similar to the self and provide the first empirical demonstration that synchrony-induced affiliation modulates emotional responding and altruism.     

Infants' intermodal perception of two levels of temporal structure in natural events

Infants' intermodal perception of two levels of temporal structure uniting the visual and acoustic stimulation from natural, complex events was investigated in four experiments. Films depicting a single object (single, large marble) and a compound object (group of smaller marbles) colliding against a surface in an erratic pattern were presented to infants between 3 and months of age using an intermodal preference and search method. These stimulus events portrayed two levels of invariant temporal structure: (a) temporal synchrony united the sights and sounds of object impact, and (b) temporal microstructure, the internal temporal structure of each impact sound and motion, specified the composition of the object (single vs. compound). Experiment 1 demonstrated that by 6 months infants detected a relation between the audible and visible stimulation from these events when both levels of invariant temporal structure guided their intermodal exploration. Experiment 2 revealed that by 6 months infants detected the bimodal temporal microstructure specifying object composition. They looked predominantly to the film whose natural soundtrack was played even though the motions of objects in both films were synchronized with the soundtrack. Experiment 3 assessed infants' sensitivity to temporal synchrony relations. Two films depicting objects of the same composition were presented while the motions of only one of them was synchronized with the appropriate soundtrack. Both 6-month-olds showed evidence of detecting temporal synchrony relations under some conditions. Experiment 4 examined how temporal synchrony and temporal microstructure interact in directing intermodal exploration. The natural soundtrack to one of the objects was played out-of-synchrony with the motions of both. In contrast with the results of Experiment 2, infants at 6 months showed no evidence of detecting a relationship between the film and its appropriate soundtrack. This suggests that the temporal asynchrony disrupted their detection of the temporal microstructure specifying object composition. Results of these studies support on invariant-detection view of the development of intermodal perception.     

Coordination Dynamics of the Horse-Rider System

The authors studied the interaction between rider and horse by measuring their ensemble motions in a trot sequence, comparing 1 expert and 1 novice rider. Whereas the novice's movements displayed transient departures from phase synchrony, the expert's motions were continuously phase-matched with those of the horse. The tight ensemble synchrony between the expert and the horse was accompanied by an increase in the temporal regularity of the oscillations of the trunk of the horse. Observed differences between expert and novice riders indicated that phase synchronization is by no means perfect but requires extended practice. Points of contact between horse and rider may haptically convey effective communication between them.     

Temporal binding and the neural correlates of sensory awareness

Theories of binding have recently come into the focus of the consciousness debate. In this review, we discuss the potential relevance of temporal binding mechanisms for sensory awareness. Specifically, we suggest that neural synchrony with a precision in the millisecond range may be crucial for conscious processing, and may be involved in arousal, perceptual integration, attentional selection and working memory. Recent evidence from both animal and human studies demonstrates that specific changes in neuronal synchrony occur during all of these processes and that they are distinguished by the emergence of fast oscillations with frequencies in the gamma-range.     

Regional and inter-regional theta oscillation during episodic novelty processing

Recent event-related potential (ERP) and functional magnetic resonance imaging (fMRI) studies suggest that novelty processing may be involved in processes that recognize the meaning of a novel sound, during which widespread cortical regions including the right prefrontal cortex are engaged. However, it remains unclear how those cortical regions are functionally integrated during novelty processing. Because theta oscillation has been assumed to have a crucial role in memory operations, we examined local and inter-regional neural synchrony of theta band activity during novelty processing. Fifteen right-handed healthy university students participated in this study. Subjects performed an auditory novelty oddball task that consisted of the random sequence of three types of stimuli such as a target (1000 Hz pure tone), novel (familiar environmental sounds such as dog bark, buzz, car crashing sound and so on), and standard sounds (950 Hz pure tone). Event-related spectra perturbation (ERSP) and the phase-locking value (PLV) were measured from human scalp EEG during task. Non-parametric statistical tests were applied to test for significant differences between stimulus novelty and stimulus targets in ERSP and PLV. The novelty P3 showed significant higher amplitude and shorter latency compared with target P3 in frontocentral regions. Overall, theta activity was significantly higher in the novel stimuli compared with the target stimuli. Specifically, the difference in theta power between novel and target stimuli was most significant in the right frontal region. This right frontal theta activity was accompanied by phase synchronization with the left temporal region. Our results imply that theta phase synchronization between right frontal and left temporal regions underlie the retrieval of memory traces for unexpected but familiar sounds from long term memory in addition to working memory retrieval or novelty encoding.     

A synchronization effect and its application to stuttering by a portable apparatus

The present study attempted to determine how a rhythmic beat affects ongoing behavior. A regular stimulus beat was presented to normal subjects who had been instructed to push a bar from side to side. Other subjects had been instructed to emit a vocal response. The individual vocal and motor responses became synchronized with the individual beats of the rhythm. The time between stimulus beats determined the modal interresponse time. These results indicate a synchronization effect: ongoing behavior tends to become synchronized with an ongoing stimulus rhythm. An attempt was made to apply these findings to the problem of stuttering, which can be considered as a disturbance of the natural rhythm of speech. Stutterers were instructed to synchronize their speech with a simple regular beat presented to them tactually by a portable apparatus. The result was a reduction of 90% or more of the stuttering for each subject during the period of synchronization. This effect endured for extended periods of spontaneous speech as well as for reading aloud and was found to be attributable to the rhythmic nature of the stimulus and not to other factors.     

Mechanisms and evolution of synchronous chorusing: emergent properties and adaptive functions in Neoconocephalus katydids (Orthoptera: Tettigoniidae)

Synchronous interactions arise in various animal species that rhythmically broadcast acoustic, vibratory, and visual signals. These interactions are characterized by a coincidence in both rate and phase of the rhythms of neighboring signalers. Theory predicts several ways in which synchronized rhythms may specifically benefit the interacting signalers. However, synchrony may also arise as an emergent property, a default phenomenon that is neither preferred by conspecific receivers evaluating the signals nor advantageous to the signalers themselves. Here, we examine several well-studied cases of acoustic synchrony in Neoconocephalus katydids (Orthoptera: Tettigoniidae), a New World genus wherein males broadcast loud advertisement songs. We report that call synchrony found in N. spiza and N. nebrascensis results from two rather different mechanisms of rhythm adjustment. Moreover, synchrony in the former species appears to represent an incidental byproduct of signal competition between evenly matched males, whereas in the latter species synchrony functions as a specific adaptation in which cooperating males ensure that critical call features can be perceived by females. We discuss the separate evolutionary trajectories that may have led to similar outcomes, synchronous chorusing by advertising males, in these closely related species.     

Rapid motor adaptations to subliminal frequency shifts during syncopated rhythmic sensorimotor synchronization

The synchronization of rhythmic arm movements to a syncopated metronome cue was studied in a step-change design whereby small tempo shifts were inserted at fixed time points into the metronome frequency. The cueing sequence involved three stimulus types: (1) target contact in synchrony with the metronome beats, (2) syncopated target contact midway in time between audible beats, and (3) syncopated target contact following either a +2% or -2% change in stimulus frequency. Analysis of normalized and aggregated data revealed that (1) during the syncopation condition the response period showed a rapid adaptation to the frequency-incremented stimulus period, (2) response period was less variable during syncopated movement, (3) mean synchronization error and variability, calculated during syncopation relative to the mathematical midpoint of the stimulus cycle, were reduced during syncopated movements, and (4) synchronization error following the frequency increment showed trends to return linearly to pre-increment values which was fully achieved in the -2% change condition only. The results suggest that frequency entrainment to stimulus period was possible during syncopated movement with the response and stimulus onsets 180 degrees out of phase. Most remarkably, 70-80% of the adaptation of the response period to the new stimulus period was immediately attained during the second half cycle of the syncopated movement. Finally, a mathematical model, based on recursion, was introduced that accurately modeled actual data as a function of the previous stimulus and response intervals and a weighted response of period error and synchronization error, which showed dominance of frequency entrainment over phase entrainment during rhythmic synchronization.     

Neural Mechanisms of Visual Feature Binding Investigated with Microelectrodes and Models

A single object generally activates neurones in many visual cortical areas corresponding to a distributed representation of its features. Itis still under debate how the distributed representation of an objectis bound intoa coherent whole and how unrelated features are separated. Synchronization of neural signals has been proposed to code spatial feature binding, supported by the discovery of synchronized assemblies in visual cortex. Synchronizations are either fast oscillatory (30–90 Hz) cortically generated events, or non-rhythmical stimulus-locked responses, depending on the visual stimulation. The cortical range over which synchronizations occur, transformed to visual space, is generally several times larger than the classical receptive fields (CRF) of neurones in lower visual cortex areas. However, the cortical regions synchronized by fastoscillations do notspan the representational range of larger objects but only parts of it. To relate such restricted segments to perceptual processes the concept of the association field (AF) of local neural assemblies was introduced in accordance with CRFs of single neurones. Here an AF is composed of the aggregate of CRFs of an assembly engaged in a common synchronized state. Itis argued thatspatial continuity of an object is coded by a continuum of overlapping AFs, that is, by overlapping regions of phase coupled neurones. Hence, object continuity would be represented by phase continuity. Besides feature binding, feature separation is necessary for scene segmentation. Separation may be coded by functional decoupling causing uncorrelated activities or by mutual inhibition leading to alternating activations in assemblies of separate representations. A third temporal coding aspect is temporal segmentation by the shortactivation-inhibition cycles of fast oscillations orshorttransientstimulus-locked responses, which may preventperceptual “smearing” by interrupting the flow of visual information into precisely defined frames. The presentpaperalso aims atrelating signals of stimulus dependentsynchronization and desynchronization with basic neural mechanisms and circuits. Finally, the synchronization hypothesis is critically discussed with respect to contradictory psychophysical work and supportive new recording results, including evidence for perception-related synchronizations.     

Synchronized cortical potentials and wavelet packets: a potential mechanism for perceptual binding and conveying information

Temporal synchronization in neuronal assemblies has been linked to the functional roles of perceptual binding, sensory-motor integration, attention, and information coding. We report new evidence for a common underlying mechanism that uses specific temporal patterns of synchronized neuronal activity as a basis for conveying information. The temporal patterns of stimulus-related synchronized neuronal discharges are structured to closely resemble specific members of the Symlet wavelet packet family employed in a computational framework. Together, these results suggest that temporal patterns of synchronized activity may act as a parallel, distributed code for information through a mechanism computationally equivalent to wavelet packet analysis.     

Adaptation to altered visual—vestibular feedback: Mechanisms of maintenance and recovery

Adaptation of perceived movement during head motion (apparent concomitant motion, ACM) and the subsequent elimination of adaptation were studied in two experiments. During the adaptation phase of both experiments, subjects performed voluntary 1-Hz head oscillations for 6 min while fixating a stimulus moving either in the same (with) direction as or the opposite (against) direction of head movements. In Experiment 1, ACM adaptation was measured following either a 1- or a 4-min delay after the adaptation phase. Results indicated some loss of adaptation during the additional 3-min delay, demonstrating a tendency of the system linking head and image to return to its preadaptation state following removal of an adaptation stimulus. In Experiment 2, subjects viewed a stimulus after adaptation that appeared to move minimally in the same manner as the adaptation stimulus during 3 min of head oscillations. No loss of adaptation was measured in these subjects between the beginning and the end of the 3-min interval. In another condition, subjects viewed a stimulus that appeared to move alternately in the same direction as and in the opposite direction of the adaptation stimulus during a similar 3-min interval following adaptation. ACM adaptation was substantially reduced during this 3-min interval. These results implicate two mechanisms that operate to either maintain or eliminate ACM adaptation. One is passive and operates in the absence of visual feedback to eliminate the short-term adapted state, and the other responds to postadaptation visual feedback.     

The effects of subthreshold synchrony on the perception of simultaneity

We aimed to examine the effects of subthreshold synchrony and asynchrony on the perception of simultaneity. We rendered simultaneous or asynchronous luminance changes below detection thresholds by embedding them in a sequence of rapidly onsetting flankers. Still, simultaneity of subthreshold luminance changes can influence decisions concerning the simultaneity of clearly visible changes in luminance: across a range of very brief target SOAs, subthreshold synchrony was found to increase the tendency to report ‘simultaneity’, although simultaneity thresholds themselves remained largely uninfluenced. These effects are discussed in terms of the early synchronization of sensory mechanisms and the extent to which this pattern of synchronization influences the perception of relations between events in time.     

Induced motion considered as a visually induced oculogyral illusion

The possibility that nystagmus suppression contributes to illusory motion was investigated by measuring perceived motion of a stationary stimulus following the removal of an optokinetic stimulus. This was done because optokinetic nystagmus typically outlasts cessation of an optokinetic stimulus. Therefore, it would be expected that a stationary fixated stimulus should appear to move after removal of an optokinetic stimulus if illusory motion results from nystagmus suppression. Illusory motion was reported for a stationary fixation target following optokinetic stimulation. This motion was reported first in the same direction as the preceding induced motion, then in the opposite direction. The two directions of illusory motion following optokinetic stimulation are interpreted as resulting from the use of smooth ocular pursuit to suppress first one phase of optokinetic after nystagmus and then the reverse phase. Implications for the origins of induced motion are discussed.     

Judgments of synchrony between auditory and moving or still visual stimuli.

The flash-lag effect is a visual illusion wherein intermittently flashed, stationary stimuli seem to trail after a moving visual stimulus despite being flashed synchronously. We tested hypotheses that the flash-lag effect is due to spatial extrapolation, shortened perceptual lags, or accelerated acquisition of moving stimuli, all of which call for an earlier awareness of moving visual stimuli over stationary ones. Participants judged synchrony of a click either to a stationary flash of light or to a series of adjacent flashes that seemingly bounced off or bumped into the edge of the visual display. To be judged synchronous with a stationary flash, audio clicks had to be presented earlier--not later--than clicks that went with events, like a simulated bounce (Experiment 1) or crash (Experiments 2-4), of a moving visual target. Click synchrony to the initial appearance of a moving stimulus was no different than to a flash, but clicks had to be delayed by 30-40 ms to seem synchronous with the final (crash) positions (Experiment 2). The temporal difference was constant over a wide range of motion velocity (Experiment 3). Interrupting the apparent motion by omitting two illumination positions before the last one did not alter subjective synchrony, nor did their occlusion, so the shift in subjective synchrony seems not to be due to brightness contrast (Experiment 4). Click synchrony to the offset of a long duration stationary illumination was also delayed relative to its onset (Experiment 5). Visual stimuli in motion enter awareness no sooner than do stationary flashes, so motion extrapolation, latency difference, and motion acceleration cannot explain the flash-lag effect.     

Peak velocity as a cue in audiovisual synchrony perception of rhythmic stimuli

This study investigated audiovisual synchrony perception in a rhythmic context, where the sound was not consequent upon the observed movement. Participants judged synchrony between a bouncing point-light figure and an auditory rhythm in two experiments. Two questions were of interest: (1) whether the reference in the visual movement, with which the auditory beat should coincide, relies on a position or a velocity cue; (2) whether the figure form and motion profile affect synchrony perception. Experiment 1 required synchrony judgment with regard to the same (lowest) position of the movement in four visual conditions: two figure forms (human or non-human) combined with two motion profiles (human or ball trajectory). Whereas figure form did not affect synchrony perception, the point of subjective simultaneity differed between the two motions, suggesting that participants adopted the peak velocity in each downward trajectory as their visual reference. Experiment 2 further demonstrated that, when judgment was required with regard to the highest position, the maximal synchrony response was considerably low for ball motion, which lacked a peak velocity in the upward trajectory. The finding of peak velocity as a cue parallels results of visuomotor synchronization tasks employing biological stimuli, suggesting that synchrony judgment with rhythmic motions relies on the perceived visual beat.     

工作记忆的神经振荡调控：基于神经振荡夹带现象

工作记忆的神经振荡机制研究是当前记忆领域的研究热点之一。那么, 神经振荡仅仅是工作记忆过程的伴随现象, 还是直接参与并调控了工作记忆的加工过程?已有研究发现, 大脑内部的神经振荡活动在外界节律性刺激的驱动下, 逐步与外界刺激节律相位同步化, 这一现象被称为“神经振荡夹带”。重复经颅磁刺激(repetitive Transcranial Magnetic Stimulation, rTMS)和经颅交流电刺激(transcranial Alternating Current Stimulation, tACS)干预研究基于此现象, 对大脑局部脑区施加节律性磁、电刺激, 进而调控工作记忆过程中特定频段的神经振荡活动、跨频段的神经振荡耦合或跨脑区的神经振荡相位同步, 为神经振荡参与工作记忆加工提供较为直接的因果证据。未来研究需考虑从脑网络的角度出发, 调控多个脑区之间的神经振荡活动, 进一步考察神经振荡对工作记忆的影响。此外, 还需注意探索和优化rTMS/tACS调控工作记忆的刺激方案, 并辅以客观的脑电记录, 提高该类研究的有效性和可重复性, 最终达到提高工作记忆能力的目的。     

Simultaneous Event-Based and Emergent Timing: Synchronization,Continuation, and Phase Correction

It has been claimed that rhythmic tapping and circle drawing represent fundamentally different timing processes (event-based and emergent, respectively) and also that circle drawing is difficult to synchronize with a metronome and exhibits little phase correction. In the present study, musically trained participants tapped with their left hands, drew circles with their right (dominant) hands, and also performed both tasks simultaneously. In Experiment 1, they synchronized with a metronome and then continued on their own, whereas in Experiment 2, they synchronized with a metronome containing phase perturbations. Circle drawing generally exhibited reliable synchronization, although with greater variability than tapping, and also showed a clear phase-correction response that evolved gradually during the cycle immediately following a perturbation. When carried out simultaneously in synchrony, with or without a metronome, the two tasks affected each other in some ways but retained their distinctive timing characteristics. This shows that event-based and emergent timing can coexist in a dual-task situation. Furthermore, the authors argue that the two timing modes usually coexist in each individual task, although one mode is often dominant.     

EEG phase synchronization during semantic unification relates to individual differences in children’s vocabulary skill

As we listen to speech, our ability to understand what was said requires us to retrieve and bind together individual word meanings into a coherent discourse representation. This so‐called semantic unification is a fundamental cognitive skill, and its development relies on the integration of neural activity throughout widely distributed functional brain networks. In this proof‐of‐concept study, we examine, for the first time, how these functional brain networks develop in children. Twenty‐six children (ages 4–17) listened to well‐formed sentences and sentences containing a semantic violation, while EEG was recorded. Children with stronger vocabulary showed N400 effects that were more concentrated to centroparietal electrodes and greater EEG phase synchrony (phase lag index; PLI) between right centroparietal and bilateral frontocentral electrodes in the delta frequency band (1–3 Hz) 1.27–1.53 s after listening to well‐formed sentences compared to sentences containing a semantic violation. These effects related specifically to individual differences in receptive vocabulary, perhaps pointing to greater recruitment of functional brain networks important for top‐down semantic unification with development. Less skilled children showed greater delta phase synchrony for violation sentences 3.41–3.64 s after critical word onset. This later effect was partly driven by individual differences in nonverbal reasoning, perhaps pointing to non‐verbal compensatory processing to extract meaning from speech in children with less developed vocabulary. We suggest that functional brain network communication, as measured by momentary changes in the phase synchrony of EEG oscillations, develops throughout the school years to support language comprehension in different ways depending on children's verbal and nonverbal skill levels.