Spacetime in the brain: rapid brain network reorganization in visual processing and recovery.

Functional connectivity networks (FCN) are the physiological basis of brain synchronization to integrating neural activity. They are not rigid but can reorganize under pathological conditions or during mental or behavioral states. However, because mental acts can be very fast, like the blink of an eye, we now used the visual system as a model to explore rapid FCN reorganization and its functional impact in normal, abnormal and post treatment vision. EEG-recordings were time-locked to visual stimulus presentation; graph analysis of neurophysiological oscillations were used to characterize millisecond FCN dynamics in healthy subjects and in patients with optic nerve damage before and after neuromodulation with alternating currents stimulation and were correlated with visual performance. We showed that rapid and transient FCN synchronization patterns in humans can evolve and dissolve in millisecond speed during visual processing. This rapid FCN reorganization is functionally relevant because disruption and recovery after treatment in optic nerve patients correlated with impaired and recovered visual performance, respectively. Because FCN hub and node interactions can evolve and dissolve in millisecond speed to manage spatial and temporal neural synchronization during visual processing and recovery, we propose "Brain Spacetime" as a fundamental principle of the human mind not only in visual cognition but also in vision restoration.

Gamma-band synchronisation in a frontotemporal auditory information processing network.

Neural oscillations are fundamental mechanisms of the human brain that enable coordinated activity of different brain regions during perceptual and cognitive processes. A frontotemporal network generated by means of gamma oscillations and comprising the auditory cortex (AC) and the anterior cingulate cortex (ACC) has been shown to be involved in the cognitively demanding auditory information processing. This study aims to reveal patterns of functional and effective connectivity within this network in healthy subjects by means of simultaneously recorded electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). We simultaneously recorded EEG and fMRI in 28 healthy subjects during the performance of a cognitively demanding auditory choice reaction task. Connectivity between the ACC and AC was analysed employing EEG and fMRI connectivity measures. We found a significant BOLD signal correlation between the ACC and AC, a significant task-dependant increase of fMRI connectivity (gPPI) and a significant increase in functional coupling in the gamma frequency range between these regions (LPS), which was increased in top-down direction (granger analysis). EEG and fMRI connectivity measures were positively correlated. The results of these study point to a role of a top-down influence of the ACC on the AC executed by means of gamma synchronisation. The replication of fMRI connectivity patterns in simultaneously recorded EEG data and the correlation between connectivity measures from both domains found in our study show, that brain connectivity based on the synchronisation of gamma oscillations is mirrored in fMRI connectivity patterns.

Analysis of selective attention processing on experienced simultaneous interpreters using EEG phase synchronization.

This study analyzed the selective attention processing related to cognitive load on simultaneous interpretation (SI). We tested simultaneous interpreter's brain function using EEG signals and calculated inter-trial coherence (ITC) extracted by the 40-Hz auditory steady-state response (ASSR). In this experiment, we set two conditions as Japanese-English translation and Japanese shadowing cognition. We also compared two subject groups: S rank with more than 15 years of SI experience (n=7) and C rank with less than one year experience (n=15). As a result, the ITCs for S rank in interpreting conditions were more significantly increased than C rank in the shadowing conditions (ITC: p<0.001). Our results demonstrate that 40-Hz ASSR might be a good indicator of selective attention and cognitive load during SI in ecologically valid environmental conditions. It can also be used to detect attention and cognitive control dysfunction in ADHD or schizophrenia.

Music as a scaffold for listening to speech: Better neural phase-locking to song than speech.

Neural activity synchronizes with the rhythmic input of many environmental signals, but the capacity of neural activity to entrain to the slow rhythms of speech is particularly important for successful communication. Compared to speech, song has greater rhythmic regularity, a more stable fundamental frequency, discrete pitch movements, and a metrical structure, this may provide a temporal framework that helps listeners neurally track information better than the rhythmically irregular rhythms of speech. The current study used EEG to examine whether entrainment to the syllable rate of linguistic utterances, as indexed by cerebro-acoustic phase coherence, was greater when listeners heard sung than spoken sentences. We assessed listeners phase-locking in both easy (no time compression) and hard (50% time-compression) utterance conditions. Adults phase-locked equally well to speech and song in the easy listening condition. However, in the time-compressed condition, phase-locking was greater for sung than spoken utterances in the theta band (3.67-5 â€‹Hz). Thus, the musical temporal and spectral characteristics of song related to better phase-locking to the slow phrasal and syllable information (4-7 â€‹Hz) in the speech stream. These results highlight the possibility of using song as a tool for improving speech processing in individuals with language processing deficits, such as dyslexia.

Linking alpha oscillations, attention and inhibitory control in adult ADHD with EEG neurofeedback.

Abnormal patterns of electrical oscillatory activity have been repeatedly described in adult ADHD. In particular, the alpha rhythm (8-12 Hz), known to be modulated during attention, has previously been considered as candidate biomarker for ADHD. In the present study, we asked adult ADHD patients to self-regulate their own alpha rhythm using neurofeedback (NFB), in order to examine the modulation of alpha oscillations on attentional performance and brain plasticity. Twenty-five adult ADHD patients and 22 healthy controls underwent a 64-channel EEG-recording at resting-state and during a Go/NoGo task, before and after a 30 min-NFB session designed to reduce (desynchronize) the power of the alpha rhythm. Alpha power was compared across conditions and groups, and the effects of NFB were statistically assessed by comparing behavioral and EEG measures pre-to-post NFB. Firstly, we found that relative alpha power was attenuated in our ADHD cohort compared to control subjects at baseline and across experimental conditions, suggesting a signature of cortical hyper-activation. Both groups demonstrated a significant and targeted reduction of alpha power during NFB. Interestingly, we observed a post-NFB increase in resting-state alpha (i.e. rebound) in the ADHD group, which restored alpha power towards levels of the normal population. Importantly, the degree of post-NFB alpha normalization during the Go/NoGo task correlated with individual improvements in motor inhibition (i.e. reduced commission errors) only in the ADHD group. Overall, our findings offer novel supporting evidence implicating alpha oscillations in inhibitory control, as well as their potential role in the homeostatic regulation of cortical excitatory/inhibitory balance.

Evidence that alpha blocking is due to increases in system-level oscillatory damping not neuronal population desynchronisation.

The attenuation of the alpha rhythm following eyes-opening (alpha blocking) is among the most robust features of the human electroencephalogram with the prevailing view being that it is caused by changes in neuronal population synchrony. To further study the basis for this phenomenon we use theoretically motivated fixed-order Auto-Regressive Moving-Average (ARMA) time series modelling to study the oscillatory dynamics of spontaneous alpha-band electroencephalographic activity in eyes-open and eyes-closed conditions and its modulation by the NMDA antagonist ketamine. We find that the reduction in alpha-band power between eyes-closed and eyes-open states is explicable in terms of an increase in the damping of stochastically perturbed alpha-band relaxation oscillatory activity. These changes in damping are putatively modified by the antagonism of NMDA-mediated glutamatergic neurotransmission but are not directly driven by changes in input to cortex nor by reductions in the phase synchronisation of populations of near identical oscillators. These results not only provide a direct challenge to the dominant view of the role that thalamus and neuronal population de-/synchronisation have in the genesis and modulation of alpha electro-/magnetoencephalographic activity but also suggest potentially important physiological determinants underlying its dynamical control and regulation.

Modulation Effect of Acupuncture on Functional Brain Networks and Classification of Its Manipulation With EEG Signals.

Acupuncture manipulation is the key of Chinese medicine acupuncture therapy. In clinical practice, different acupuncture manipulations are required to achieve different therapeutic effects, which means it is crucial to distinguish different acupuncture manipulations. In this paper, we proposed a classification framework for different acupuncture manipulations, which employed the graph theory and machine learning method. Multichannel EEG signals evoked by acupuncture at "Zusanli" acupoint were recorded from healthy humans by two acupuncture manipulations: twirling-rotating (TR) and lifting-thrusting (LT). Phase locking value was used to estimate the phase synchronization of pair-wise EEG channels. It was found that acupunctured by TR manipulation exhibit significantly higher synchronization degree than acupunctured by LT manipulation. With the construction of functional brain network, the topological features of graph theory were extracted. Taken the network features as inputs, machine learning classifiers were established to classify acupuncture manipulations. The highest accuracy can achieve 92.14% with support vector machine. By further optimizing the network features utilized in machine learning classifiers, it was found that the combination of node betweenness and small world network index is the most effective factor for acupuncture manipulations classification. These findings suggested that our approach provides new ideas for automatically identify acupuncture manipulations from the perspective of functional brain networks and machine learning methods.

Neurophysiological Correlates of Gait Retraining With Real-Time Visual and Auditory Feedback.

Most people acquire motor skills through feedback-based training. How the human brain processes sensory feedbacks during training, especially in a gait training, remain largely unclear. The purpose of this paper is to explore how humans adopt a new gait pattern to reduce impacts during walking-with the aid of visual and audio feedbacks. This paper demonstrates the features of underlying brain activity in incorporating the visual or auditory cues to acquire a new gait pattern. Electroencephalography (EEG) and peak positive acceleration (PPA) of the heel were collected from 23 participants during walking on a treadmill with no feedback, with visual feedback, or with audio feedback. The feedbacks were presented after each foot strike, where a sub-threshold PPA triggered a positive feedback (green/low-pitched), and a suprathreshold PPA triggered a negative feedback (red/high-pitched). The participants were instructed to voluntarily control their gait, so that low PPA could be achieved. This control was perturbed in some sessions by an additional cognitive task, and the influence of such distraction was also explored. The PPA was significantly lower in the sessions with visual or audio feedback than in sessions without feedback, showing an immediate improvement in gait pattern, when the feedback was provided. Different feedbacks modulated neural activities at different locations and/or levels during training. Alpha event-related synchronization (ERS) was particularly increased during the encoding of auditory feedback or the introduction of a distracting task. In the meantime, prominent frontal and posterior theta ERS were coupled with negative feedback, and strong beta event-related desynchronization (ERD) was observed only in sessions with feedbacks. Our results indicate that feedback effectively enhances motor planning when acquiring a new gait.

BCI Monitor Enhances Electroencephalographic and Cerebral Hemodynamic Activations During Motor Training.

Motor imagery-based brain-computer interface (MI-BCI) controlling functional electrical stimulation (FES) is promising for disabled patients to restore their motor functions. However, it remains unclear how much the BCI part can contribute to the functional coupling between the brain and muscle. Specifically, whether it can enhance the cerebral activation for motor training? Here, we investigate the electroencephalographic and cerebral hemodynamic responses for MI-BCI-FES training and MI-FES training, respectively. Twelve healthy subjects were recruited in the motor training study when concurrent electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) were recorded. Compared with the MI-FES training conditions, the MI-BCI-FES could induce significantly stronger event-related desynchronization (ERD) and blood oxygen response, which demonstrates that BCI indeed plays a functional role in the closed-loop motor training. Therefore, this paper verifies the feasibility of using BCI to train motor functions in a closed-loop manner.

Phase synchrony in slow cortical potentials is decreased in both expert and trained novice meditators.

Neuronal interactions coupled by phase synchronization have been studied in a wide range of frequency bands, but fluctuations below the delta frequency have often been neglected. In the present study, phase synchrony in slow cortical potentials (SCPs, 0.01-0.1 Hz) was examined during two different mental states; a resting state and a breath-focused mindfulness meditation. SCP phase synchrony in 9 long-term expert meditators (on average 22 years of experience) were compared with the data obtained from 11 novices. Additionally, after the novices attended an 8-week mindfulness-based stress reduction (MBSR) program, SCP phase synchrony was measured again. While expert meditators and novices exhibited the same amount of SCP phase synchrony in the resting state, decreased synchronization was found during meditation among expert meditators as well as novices who had participated in the MBSR program (but not prior to the program). These findings suggest that phase synchrony in slow cortical activity is context-dependent and could provide crucial information in the study of the human mind.

Significance and Translational Value of High-Frequency Cortico-Basal Ganglia Oscillations in Parkinson's Disease.

The mechanisms and significance of basal ganglia oscillations is a fundamental research question engaging both clinical and basic investigators. In Parkinson's disease (PD), neural activity in basal ganglia nuclei is characterized by oscillatory patterns that are believed to disrupt the dynamic processing of movement-related information and thus generate motor symptoms. Beta-band oscillations associated with hypokinetic states have been reviewed in several excellent previous articles. Here we focus on faster oscillatory phenomena that have been reported in association with a diverse range of motor states. We review the occurrence of different types of fast oscillations and the evidence supporting their pathophysiological role. We also provide a general discussion on the definition, possible mechanisms, and translational value of synchronized oscillations of different frequencies in cortico-basal ganglia structures. Revealing how oscillatory phenomena are caused and spread in cortico-basal ganglia-thalamocortical networks will offer a key to unlock the neural codes of both motor and non-motor symptoms in PD. In preclinical therapeutic research, recording of oscillatory neural activities holds the promise to unravel mechanisms of action of current and future treatments.

Modulation of Spectral Power and Functional Connectivity in Human Brain by Acupuncture Stimulation.

Acupuncture, as an external stimulation, can produce clinical effects via the central nervous system. In order to investigate the modulatory efficacy of acupuncture on brain activity, multichannel EEG signals evoked by acupuncture at "Zusanli" acupoint were recorded from healthy humans in three states: pre-acupuncture, acupuncture, and post-acupuncture. Power spectral density is first used to analyze the EEG power change during acupuncture process. It is found that EEG power significantly increased in the delta and alpha bands under acupuncture and high power level remained in alpha band after acupuncture. Then, we calculated phase lag index to quantify the phase synchronization of pair-wise channels. In acupuncture state, delta and alpha bands exhibit significantly higher synchronization degree than pre-acupuncture state. Additionally, post-effect of acupuncture can be observed in alpha band as high synchronization degree remains in post-acupuncture state. Moreover, functional brain networks converted from synchronization matrix in each band are reconstructed. Acupuncture increases long-range connections between left and right hemispheres and changes the position of main nodes. Graph theory metrics are extracted to explore the change of functional connectivity in different states. The result shows the functional networks in delta and alpha bands are small world networks (SWN) and acupuncture improves the SWN efficiency of functional network.

Response properties of the human frequency-following response (FFR) to speech and non-speech sounds: level dependence, adaptation and phase-locking limits.

OBJECTIVE: The frequency-following response (FFR) is a neurophonic potential used to assess auditory neural encoding at subcortical stages. Despite the FFR's empirical and clinical utility, basic response properties of this evoked potential remain undefined. DESIGN: We measured FFRs to speech and nonspeech (pure tone, chirp sweeps) stimuli to quantify three key properties of this potential: level-dependence (I/O functions), adaptation and the upper limit of neural phase-locking. STUDY SAMPLE: n = 13 normal-hearing listeners. RESULTS: I/O functions showed FFR amplitude increased with increasing stimulus presentation level between 25 and 80 dB SPL; FFR growth was steeper for tones than speech when measured at the same frequency. FFR latency decreased 4-5 ms with decreasing presentation level from 25 and 80 dB SPL but responses were ∼2 ms earlier for speech than tones. FFR amplitudes showed a 50% reduction over 6 min of recording with the strongest adaptation in the first 60 s (250 trials). Estimates of neural synchronisation revealed FFRs contained measurable phase-locking up to ∼1200-1300 Hz, slightly higher than the single neuron limit reported in animal models. CONCLUSIONS: Findings detail fundamental response properties that will be important for using FFRs in clinical and empirical applications.

Neural responses to perturbations in visual and auditory metronomes during sensorimotor synchronization.

Tapping in synchrony to an isochronous rhythm involves several key functions of the sensorimotor system including timing, prediction and error correction. While auditory sensorimotor synchronization (SMS) has been well studied, much less is known about mechanisms involved in visual SMS. By comparing error correction in auditory and visual SMS, it can be determined if the neural mechanisms for detection and correction of synchronization errors are generalized or domain specific. To study this problem, we measured EEG while subjects tapped in synchrony to separate visual and auditory metronomes that both contained small temporal perturbations to induce errors. The metronomes had inter-onset intervals of 600 ms and the perturbations where of 4 kinds: ± 66 ms to induce period corrections, and ± 16 ms to induce phase corrections. We hypothesize that given the less precise nature of visual SMS, error correction to perturbed visual flashing rhythms will be more gradual than with the equivalent auditory perturbations. Additionally, we expect this more gradual error correction will be reflected in the visual evoked potentials. Our findings indicate that the visual system is only capable of more gradual phase corrections to even the larger induced errors. This is opposed to the swifter period correction of the auditory system to large induced errors. EEG data found the peak N1 auditory evoked potential is modulated by the size and direction of an induced error in line with previous research, while the P1 visual evoked potential was only effected by the large late-coming perturbations resulting in reduced peak latency. Looking at the error response EEG data, an Error Related Negativity (ERN) and related Error Positivity (pE) was found only in the auditory + 66 condition, while no ERN or pE were found in any of the visual perturbation conditions. In addition to the ERPs, we performed a dipole source localization and clustering analysis indicating that the anterior cingulate was active in the error detection of the perturbed stimulus for both auditory and visual conditions in addition to being involved in producing the ERN and pE induced by the auditory + 66 perturbation. Taken together, these results confirm that the visual system is less developed for synchronizing and error correction with flashing rhythms by its more gradual error correction. The reduced latency of the P1 to the visual + 66 suggests that the visual system can detect these errors, but that detection does not translate into any meaningful improvement in error correction. This indicates that the visual system is not as tightly coupled to the motor system as the auditory system is for SMS, suggesting the mechanisms of SMS are not completely domain general.

Dependence of absence seizure dynamics on physiological parameter evolution.

A neural field model of the corticothalamic system is applied to investigate the temporal and spectral characteristics of absence seizures in the presence of a temporally varying connection strength between the cerebral cortex and thalamus. Increasing connection strength drives the system into an absence seizure-like state once a threshold is passed and a supercritical Hopf bifurcation occurs. The dynamics and spectral characteristics of the resulting model seizures are explored as functions of maximum connection strength, time above threshold, and the rate at which the connection strength increases (ramp rate). Our results enable spectral and temporal characteristics of seizures to be related to changes in the underlying physiological evolution of connections via nonlinear dynamics and neural field theory. Spectral analysis reveals that the power of the harmonics and the duration of the oscillations increase as the maximum connection strength and the time above threshold increase. It is also found that the time to reach the stable limit-cycle seizure oscillation from the instability threshold decreases with the square root of the ramp rate.

Long-range gamma phase synchronization as a compensatory strategy during working memory in high-performing patients with schizophrenia.

Working memory deficits in schizophrenia may be associated with impairments in the integration of neural activity across a distributed network of cortical areas. However, evaluation of the contribution of this integration to working memory impairments in patients is severely confounded by behavioral performance. In the present multidimensional-neuroimaging study, measures of neural oscillations at baseline and during a working memory task, baseline gamma-aminobutyric acid (GABA) level in the left dorsolateral prefrontal cortex (DLPFC), and behavioral performance were obtained. Controlling behavioral performance by recruiting only "high-performing" patients with schizophrenia, we investigated whether the strength of cross-area communications differs between patients with schizophrenia and healthy participants under accurate and equivalent behavioral performance. Results of phase-locking value indicated that these high-performing patients recruited significantly more between frontal and occipital regions in the left hemisphere, t(13) = -2.16, p = .05, Cohen's d = -1.20, and between frontal and temporal regions in the right hemisphere, t(13) = -2.63, p = .02, Cohen's d = -1.46. These cross-area communication patterns may be associated with visuoverbal and visuospatial working memory networks of the left and right hemispheres, respectively. Moreover, correlations of patient's cross-area communication with in vivo GABA levels of the left DLPFC revealed a significant positive relationship (r = .77, p = .04), demonstrating that the critical role of GABA functions in gamma band oscillations may go beyond local neuronal assemblies in the left DLPFC. Altogether, these exploratory findings point to the heterogeneity among schizophrenia patients and highlight the notion that high-performing patients may engage in potential compensatory mechanisms and may represent a subgroup of patients that may be categorically or dimensionally divergent in psychopathology.

Dynamic phase alignment of ongoing auditory cortex oscillations.

Neural oscillations can synchronize to external rhythmic stimuli, as for example in speech and music. While previous studies have mainly focused on elucidating the fundamental concept of neural entrainment, less is known about the time course of entrainment. In this human electroencephalography (EEG) study, we unravel the temporal evolution of neural entrainment by contrasting short and long periods of rhythmic stimulation. Listeners had to detect short silent gaps that were systematically distributed with respect to the phase of a 3 Hz frequency-modulated tone. We found that gap detection performance was modulated by the stimulus stream with a consistent stimulus phase across participants for short and long stimulation. Electrophysiological analysis confirmed neural entrainment effects at 3 Hz and the 6 Hz harmonic for both short and long stimulation lengths. 3 Hz source level analysis revealed that longer stimulation resulted in a phase shift of a participant's neural phase relative to the stimulus phase. Phase coupling increased over the first second of stimulation, but no effects for phase coupling strength were observed over time. The dynamic evolution of phase alignment suggests that the brain attunes to external rhythmic stimulation by adapting the brain's internal representation of incoming environmental stimuli.

Ipsilateral EEG mu rhythm reflects the excitability of uncrossed pathways projecting to shoulder muscles.

BACKGROUND: Motor planning, imagery or execution is associated with event-related desynchronization (ERD) of mu rhythm oscillations (8-13 Hz) recordable over sensorimotor areas using electroencephalography (EEG). It was shown that motor imagery involving distal muscles, e.g. finger movements, results in contralateral ERD correlating with increased excitability of the contralateral corticospinal tract (c-CST). Following the rationale that purposefully increasing c-CST excitability might facilitate motor recovery after stroke, ERD recently became an attractive target for brain-computer interface (BCI)-based neurorehabilitation training. It was unclear, however, whether ERD would also reflect excitability of the ipsilateral corticospinal tract (i-CST) that mainly innervates proximal muscles involved in e.g. shoulder movements. Such knowledge would be important to optimize and extend ERD-based BCI neurorehabilitation protocols, e.g. to restore shoulder movements after stroke. Here we used single-pulse transcranial magnetic stimulation (TMS) targeting the ipsilateral primary motor cortex to elicit motor evoked potentials (MEPs) of the trapezius muscle. To assess whether ERD reflects excitability of the i-CST, a correlation analysis between between MEP amplitudes and ipsilateral ERD was performed. METHODS: Experiment 1 consisted of a motor execution task during which 10 healthy volunteers performed elevations of the shoulder girdle or finger pinching while a 128-channel EEG was recorded. Experiment 2 consisted of a motor imagery task during which 16 healthy volunteers imagined shoulder girdle elevations or finger pinching while an EEG was recorded; the participants simultaneously received randomly timed, single-pulse TMS to the ipsilateral primary motor cortex. The spatial pattern and amplitude of ERD and the amplitude of the agonist muscle's TMS-induced MEPs were analyzed. RESULTS: ERDs occurred bilaterally during both execution and imagery of shoulder girdle elevations, but were lateralized to the contralateral hemisphere during finger pinching. We found that trapezius MEPs increased during motor imagery of shoulder elevations and correlated with ipsilateral ERD amplitudes. CONCLUSIONS: Ipsilateral ERD during execution and imagery of shoulder girdle elevations appears to reflect the excitability of uncrossed pathways projecting to the shoulder muscles. As such, ipsilateral ERD could be used for neurofeedback training of shoulder movement, aiming at reanimation of the i-CST.

Spatio-temporal patterns of event-related potentials related to audiovisual synchrony judgments in older adults.

Older adults have altered perception of the relative timing between auditory and visual stimuli, even when stimuli are scaled to equate detectability. To help understand why, this study investigated the neural correlates of audiovisual synchrony judgments in older adults using electroencephalography (EEG). Fourteen younger (18-32 year old) and 16 older (61-74 year old) adults performed an audiovisual synchrony judgment task on flash-pip stimuli while EEG was recorded. All participants were assessed to have healthy vision and hearing for their age. Observers responded to whether audiovisual pairs were perceived as synchronous or asynchronous via a button press. The results showed that the onset of predictive sensory information for synchrony judgments was not different between groups. Channels over auditory areas contributed more to this predictive sensory information than visual areas. The spatial-temporal profile of the EEG activity also indicates that older adults used different resources to maintain a similar level of performance in audiovisual synchrony judgments compared with younger adults.

Characterization of neural entrainment to speech with and without slow spectral energy fluctuations in laminar recordings in monkey A1.

Neural entrainment, the alignment between neural oscillations and rhythmic stimulation, is omnipresent in current theories of speech processing - nevertheless, the underlying neural mechanisms are still largely unknown. Here, we hypothesized that laminar recordings in non-human primates provide us with important insight into these mechanisms, in particular with respect to processing in cortical layers. We presented one monkey with human everyday speech sounds and recorded neural (as current-source density, CSD) oscillations in primary auditory cortex (A1). We observed that the high-excitability phase of neural oscillations was only aligned with those spectral components of speech the recording site was tuned to; the opposite, low-excitability phase was aligned with other spectral components. As low- and high-frequency components in speech alternate, this finding might reflect a particularly efficient way of stimulus processing that includes the preparation of the relevant neuronal populations to the upcoming input. Moreover, presenting speech/noise sounds without systematic fluctuations in amplitude and spectral content and their time-reversed versions, we found significant entrainment in all conditions and cortical layers. When compared with everyday speech, the entrainment in the speech/noise conditions was characterized by a change in the phase relation between neural signal and stimulus and the low-frequency neural phase was dominantly coupled to activity in a lower gamma-band. These results show that neural entrainment in response to speech without slow fluctuations in spectral energy includes a process with specific characteristics that is presumably preserved across species.