Cued spatial attention drives functionally relevant modulation of the mu rhythm in primary somatosensory cortex

Cortically-controlled population stochastic facilitation as a plausible substrate for guiding sensory transfer across the thalamic gateway

The thalamus is the primary gateway that relays sensory information to the cerebral cortex. While a single recipient cortical cell receives the convergence of many principal relay cells of the thalamus, each thalamic cell in turn integrates a dense and distributed synaptic feedback from the cortex. During sensory processing, the influence of this functional loop remains largely ignored. Using dynamic-clamp techniques in thalamic slices in vitro, we combined theoretical and experimental approaches to implement a realistic hybrid retino-thalamo-cortical pathway mixing biological cells and simulated circuits. The synaptic bombardment of cortical origin was mimicked through the injection of a stochastic mixture of excitatory and inhibitory conductances, resulting in a gradable correlation level of afferent activity shared by thalamic cells. The study of the impact of the simulated cortical input on the global retinocortical signal transfer efficiency revealed a novel control mechanism resulting from the collective resonance of all thalamic relay neurons. We show here that the transfer efficiency of sensory input transmission depends on three key features: i) the number of thalamocortical cells involved in the many-to-one convergence from thalamus to cortex, ii) the statistics of the corticothalamic synaptic bombardment and iii) the level of correlation imposed between converging thalamic relay cells. In particular, our results demonstrate counterintuitively that the retinocortical signal transfer efficiency increases when the level of correlation across thalamic cells decreases. This suggests that the transfer efficiency of relay cells could be selectively amplified when they become simultaneously desynchronized by the cortical feedback. When applied to the intact brain, this network regulation mechanism could direct an attentional focus to specific thalamic subassemblies and select the appropriate input lines to the cortex according to the descending influence of cortically-defined “priors”.

Most of the sensory information in the early visual system is relayed from the retina to the primary visual cortex through principal relay cells in the thalamus. While relay cells receive ∼7–16% of their synapses from retina, they integrate the synaptic barrage of a dense cortical feedback, which accounts for more than 60% of their total input. This feedback is thought to carry some form of “prior” resulting from the computation performed in cortical areas, which influences the response of relay cells, presumably by regulating the transfer of sensory information to cortical areas. Nevertheless, its statistical nature (input synchronization, excitation/inhibition ratio, etc.) and the cellular mechanisms gating thalamic transfer are largely ignored. Here we implemented hybrid circuits (biological and modeled cells) reproducing the main features of the thalamic gate and explored the functional impact of various statistics of the cortical input. We found that the regulation of sensory information is critically determined by the statistical coherence of the cortical synaptic bombardment associated with a stochastic facilitation process. We propose that this tuning mechanism could operate in the intact brain to selectively filter the sensory information reaching cortical areas according to attended features predesignated by the cortical feedback.

Distinguishing mechanisms of gamma frequency oscillations in human current source signals using a computational model of a laminar neocortical network

Gamma frequency rhythms have been implicated in numerous studies for their role in healthy and abnormal brain function. The frequency band has been described to encompass as broad a range as 30-150 Hz. Crucial to understanding the role of gamma in brain function is an identification of the underlying neural mechanisms, which is particularly difficult in the absence of invasive recordings in macroscopic human signals such as those from magnetoencephalography (MEG) and electroencephalography (EEG). Here, we studied features of current dipole (CD) signals from two distinct mechanisms of gamma generation, using a computational model of a laminar cortical circuit designed specifically to simulate CDs in a biophysically principled manner (Jones et al., 2007, 2009). We simulated spiking pyramidal interneuronal gamma (PING) whose period is regulated by the decay time constant of GABAA-mediated synaptic inhibition and also subthreshold gamma driven by gamma-periodic exogenous excitatory synaptic drive. Our model predicts distinguishable CD features created by spiking PING compared to subthreshold driven gamma that can help to disambiguate mechanisms of gamma oscillations in human signals. We found that gamma rhythms in neocortical layer 5 can obscure a simultaneous, independent gamma in layer 2/3. Further, we arrived at a novel interpretation of the origin of high gamma frequency rhythms (100-150 Hz), showing that they emerged from a specific temporal feature of CDs associated with single cycles of PING activity and did not reflect a separate rhythmic process. Last we show that the emergence of observable subthreshold gamma required highly coherent exogenous drive. Our results are the first to demonstrate features of gamma oscillations in human current source signals that distinguish cellular and circuit level mechanisms of these rhythms and may help to guide understanding of their functional role.

Listening to the human voice alters sensorimotor brain rhythms

While neuronal desynchronization in the mu (≈ 10 Hz) and beta (≈ 20 Hz) frequency bands has long been known to be an EEG index of sensorimotor activity, this method has rarely been employed to study auditory perception. In the present study, we measured mu and beta event-related desynchronisation (ERD) while participants were asked to listen to vocal and triangle-wave melodies and to sing them back. Results showed that mu and beta ERD began earlier and were stronger when listening to vocal compared to non-vocal melodies. Interestingly, this humanness effect was stronger for less accurate singers. These results show that voice perception favors an early involvement of motor representations.

Task-related changes in functional properties of the human brain network underlying attentional control

Previous studies have demonstrated task-related changes in brain activation and inter-regional connectivity but the temporal dynamics of functional properties of the brain during task execution is still unclear. In the present study, we investigated task-related changes in functional properties of the human brain network by applying graph-theoretical analysis to magnetoencephalography (MEG). Subjects performed a cue-target attention task in which a visual cue informed them of the direction of focus for incoming auditory or tactile target stimuli, but not the sensory modality. We analyzed the MEG signal in the cue-target interval to examine network properties during attentional control. Cluster-based non-parametric permutation tests with the Monte-Carlo method showed that in the cue-target interval, beta activity was desynchronized in the sensori-motor region including premotor and posterior parietal regions in the hemisphere contralateral to the attended side. Graph-theoretical analysis revealed that, in beta frequency, global hubs were found around the sensori-motor and prefrontal regions, and functional segregation over the entire network was decreased during attentional control compared to the baseline. Thus, network measures revealed task-related temporal changes in functional properties of the human brain network, leading to the understanding of how the brain dynamically responds to task execution as a network.

Set and setting: how behavioral state regulates sensory function and plasticity

Recently developed neuroimaging and electrophysiological techniques are allowing us to answer fundamental questions about how behavioral states regulate our perception of the external environment. Studies using these techniques have yielded surprising insights into how sensory processing is affected at the earliest stages by attention and motivation, and how new sensory information received during wakefulness (e.g., during learning) continues to affect sensory brain circuits (leading to plastic changes) during subsequent sleep. This review aims to describe how brain states affect sensory response properties among neurons in primary and secondary sensory cortices, and how this relates to psychophysical detection thresholds and performance on sensory discrimination tasks. This is not intended to serve as a comprehensive overview of all brain states, or all sensory systems, but instead as an illustrative description of how three specific state variables (attention, motivation, and vigilance [i.e., sleep vs. wakefulness]) affect sensory systems in which they have been best studied.

Infants' somatotopic neural responses to seeing human actions: I've got you under my skin

Human infants rapidly learn new skills and customs via imitation, but the neural linkages between action perception and production are not well understood. Neuroscience studies in adults suggest that a key component of imitation–identifying the corresponding body part used in the acts of self and other–has an organized neural signature. In adults, perceiving someone using a specific body part (e.g., hand vs. foot) is associated with activation of the corresponding area of the sensory and/or motor strip in the observer’s brain–a phenomenon called neural somatotopy. Here we examine whether preverbal infants also exhibit somatotopic neural responses during the observation of others’ actions. 14-month-old infants were randomly assigned to watch an adult reach towards and touch an object using either her hand or her foot. The scalp electroencephalogram (EEG) was recorded and event-related changes in the sensorimotor mu rhythm were analyzed. Mu rhythm desynchronization was greater over hand areas of sensorimotor cortex during observation of hand actions and was greater over the foot area for observation of foot actions. This provides the first evidence that infants’ observation of someone else using a particular body part activates the corresponding areas of sensorimotor cortex. We hypothesize that this somatotopic organization in the developing brain supports imitation and cultural learning. The findings connect developmental cognitive neuroscience, adult neuroscience, action representation, and behavioral imitation.

Reinforcement learning of two-joint virtual arm reaching in a computer model of sensorimotor cortex

Neocortical mechanisms of learning sensorimotor control involve a complex series of interactions at multiple levels, from synaptic mechanisms to cellular dynamics to network connectomics. We developed a model of sensory and motor neocortex consisting of 704 spiking model neurons. Sensory and motor populations included excitatory cells and two types of interneurons. Neurons were interconnected with AMPA/NMDA and GABAA synapses. We trained our model using spike-timing-dependent reinforcement learning to control a two-joint virtual arm to reach to a fixed target. For each of 125 trained networks, we used 200 training sessions, each involving 15 s reaches to the target from 16 starting positions. Learning altered network dynamics, with enhancements to neuronal synchrony and behaviorally relevant information flow between neurons. After learning, networks demonstrated retention of behaviorally relevant memories by using proprioceptive information to perform reach-to-target from multiple starting positions. Networks dynamically controlled which joint rotations to use to reach a target, depending on current arm position. Learning-dependent network reorganization was evident in both sensory and motor populations: learned synaptic weights showed target-specific patterning optimized for particular reach movements. Our model embodies an integrative hypothesis of sensorimotor cortical learning that could be used to interpret future electrophysiological data recorded in vivo from sensorimotor learning experiments. We used our model to make the following predictions: learning enhances synchrony in neuronal populations and behaviorally relevant information flow across neuronal populations, enhanced sensory processing aids task-relevant motor performance and the relative ease of a particular movement in vivo depends on the amount of sensory information required to complete the movement.

Somatosensory demands modulate muscular Beta oscillations, independent of motor demands

Neural oscillations in the beta band (15-30 Hz) occur coherently throughout the primate somatomotor network, comprising somatomotor cortices, basal ganglia, thalamus, cerebellum, and spinal cord, with the latter resulting in beta oscillations in muscular activity. In accordance with the anatomy of this network, these oscillations have traditionally been associated strictly with motor function. Here we show in humans that somatosensory demands, both in anticipation and during the processing of tactile stimuli, also modulate beta oscillations throughout this network. Specifically, somatosensory demands suppress the degree to which not only cortical activity but also muscular activity oscillates in the beta band. This suppression of muscular beta oscillations by perceptual demands is specific to demands in the somatosensory modality and occurs independent of movement preparation and execution: it occurs even when no movement is required at all. This places touch perception as an important computation within this widely distributed somatomotor beta network and suggests that, at least in healthy subjects, somatosensation and action should not be considered as separable processes, not even at the level of the muscles.

Attention-modulated alpha-band oscillations protect against intrusion of irrelevant information

Combining high-density scalp EEG recordings with a sensitive analog measure of STM's fidelity, we characterized the temporal dynamics of intentional ignoring and related those dynamics to the intrusion of task-irrelevant information. On each trial of the task, two study Gabors were briefly presented in succession. A green or red disc preceding each Gabor signified whether that Gabor should be remembered or ignored, respectively. With cue-stimulus intervals of 300, 600, or 900 msec presented in separate sessions, we found that the onset of posterior, prestimulus alpha oscillations varied with the length of the interval. Although stimulus onset time was entirely predictable, the longer the cue-stimulus interval, the earlier the increase in prestimulus alpha power. However, the alpha-band modulation was not simply locked to the cue offset. The temporal envelopes of posterior alpha-band modulation were strikingly similar for both cued attending and cued ignoring and differed only in magnitude. This similarity suggests that cued attending includes suppression of task-irrelevant, spatial processing. Supporting the view that alpha-band oscillations represent inhibition, our graded measure of recall revealed that, when the stimulus to be ignored appears second in the sequence, peristimulus alpha power predicted the degree to which that irrelevant stimulus distorted subsequent recall of the stimulus that was to be remembered. These results demonstrate that timely deployment of attention-related alpha-band oscillations can aid STM by filtering out task-irrelevant information.

Local and remote effects of transcranial direct current stimulation on the electrical activity of the motor cortical network

We systematically investigated the effects of cathodal and anodal Transcranial Direct Current Stimulation (CtDCS, AtDCS) on the electric activity of primary motor cortex during a motor task. High-density electroencephalography was used to define the spatial diffusion of tDCS after effects. Ten healthy subjects performed a finger tapping task with the right hand before and after three separate sessions of 20 minutes of Sham, AtDCS or CtDCS over left primary motor cortex (M1). During movement, we found an increment of low alpha band Event-Related Desynchronization (ERD) in bilateral central, frontal areas and in the left inferior parietal region, as well as an increment of beta ERD in fronto-central and parieto-occipital regions, after AtDCs compared to Sham and CtDCS. In the rest pre-movement period, after Sham as well as AtDCS, we documented an increment of low alpha band power over the course of pre- and post-stimulation recording sessions, localized in the sensorimotor and parieto-occipital regions. On the contrary, after CtDCS no increment of low alpha power was found. Finally beta band coherence among signals from left sensorimotor cortex and activity of bilateral parietal, occipital and right frontal regions was higher after AtDCS compared with Sham condition. Similarly, theta coherence with parietal and frontal regions was enhanced after AtDCS. We hypothesize that the local modulation of membrane polarization, as well as long-lasting synaptic modification induced by tDCS over M1, could result in changes of both local band power and functional architecture of the motor network.

Neocortical correlates of vibrotactile detection in humans

This study examined the cortical representation of vibrotactile detection in humans using event-related fMRI paired with psychophysics. Suprathreshold vibrotactile stimulation activated several areas, including primary (SI) and second somatosensory cortices (SII/PV). For threshold-level stimuli, poststimulus activity in contralateral and ipsilateral SII/PV was the best correlate of detection success. In these areas, evoked signals on hit trials were significantly greater than on missed trials in all participants, and the relative activity level across stimulation amplitudes matched perceptual performance. Activity in the anterior insula and superior temporal gyrus also correlated with hits and misses, suggesting that a "ventral stream" of somatosensory representations may play a crucial role in detection. In contrast, poststimulus activity in Area SI was not well correlated with perception and showed an overall negative response profile for threshold-level stimulation. A different correlate of detection success was, however, observed in SI. Activity in this representation immediately before stimulus onset predicted performance, a finding that was unique to SI. These findings emphasize the potential role of SII/PV in detection, the importance of state dynamics in SI for perception, and the possibility that changes in the temporal and spatial pattern of SI activity may be essential to the optimal representation of threshold-level stimuli for detection.

Oscillatory alpha modulations in right auditory regions reflect the validity of acoustic cues in an auditory spatial attention task

Anticipation of targets in the left or right hemifield leads to alpha modulations in posterior brain areas. Recently using magnetoencephalography, we showed increased right auditory alpha activity when attention was cued ipsilaterally. Here, we investigated the issue how cue validity itself influences oscillatory alpha activity. Acoustic cues were presented either to the right or left ear, followed by a compound dichotically presented target plus distractor. The preceding cue was either informative (75% validity) or uninformative (50%) about the location of the upcoming target. Cue validity × side-related alpha modulations were identified in pre- and posttarget periods in a right lateralized network, comprising auditory and nonauditory regions. This replicates and extends our previous finding of the right hemispheric dominance of auditory attentional modulations. Importantly, effective connectivity analysis showed that, in the pretarget period, this effect is accompanied by a pronounced and time-varying connectivity pattern of the right auditory cortex to the right intraparietal sulcus (IPS), with influence of IPS on superior temporal gyrus dominating at earlier intervals of the cue-target period. Our study underlines the assumption that alpha oscillations may play a similar functional role in auditory cortical regions as reported in other sensory modalities and suggests that these effects may be mediated via IPS.

Anticipation increases tactile stimulus processing in the ipsilateral primary somatosensory cortex

Stimulus anticipation improves perception. To account for this improvement, we investigated how stimulus processing is altered by anticipation. In contrast to a large body of previous work, we employed a demanding perceptual task and investigated sensory responses that occur beyond early evoked activity in contralateral primary sensory areas: Stimulus-induced modulations of neural oscillations. For this, we recorded magnetoencephalography in 19 humans while they performed a cued tactile identification task involving the identification of either a proximal or a distal stimulation on the fingertips. We varied the cue-target interval between 0 and 1000 ms such that tactile targets occurred at various degrees of anticipation. This allowed us to investigate the influence of anticipation on stimulus processing in a parametric fashion. We observed that anticipation increases the stimulus-induced response (suppression of beta-band oscillations) originating from the ipsilateral primary somatosensory cortex. This occurs in the period in which the tactile memory trace is analyzed and is correlated with the anticipation-induced improvement in tactile perception. We propose that this ipsilateral response indicates distributed processing across bilateral primary sensory cortices, of which the extent increases with anticipation. This constitutes a new and potentially important mechanism contributing to perception and its improvement following anticipation.

Frequency specific interactions of MEG resting state activity within and across brain networks as revealed by the multivariate interaction measure

Resting state networks (RSNs) are sets of brain regions exhibiting temporally coherent activity fluctuations in the absence of imposed task structure. RSNs have been extensively studied with fMRI in the infra-slow frequency range (nominally <10(-1)Hz). The topography of fMRI RSNs reflects stationary temporal correlation over minutes. However, neuronal communication occurs on a much faster time scale, at frequencies nominally in the range of 10(0)-10(2)Hz. We examined phase-shifted interactions in the delta (2-3.5 Hz), theta (4-7 Hz), alpha (8-12 Hz) and beta (13-30 Hz) frequency bands of resting-state source space MEG signals. These analyses were conducted between nodes of the dorsal attention network (DAN), one of the most robust RSNs, and between the DAN and other networks. Phase shifted interactions were mapped by the multivariate interaction measure (MIM), a measure of true interaction constructed from the maximization of imaginary coherency in the virtual channels comprised of voxel signals in source space. Non-zero-phase interactions occurred between homologous left and right hemisphere regions of the DAN in the delta and alpha frequency bands. Even stronger non-zero-phase interactions were detected between networks. Visual regions bilaterally showed phase-shifted interactions in the alpha band with regions of the DAN. Bilateral somatomotor regions interacted with DAN nodes in the beta band. These results demonstrate the existence of consistent, frequency specific phase-shifted interactions on a millisecond time scale between cortical regions within RSN as well as across RSNs.

Mindfulness starts with the body: somatosensory attention and top-down modulation of cortical alpha rhythms in mindfulness meditation

Using a common set of mindfulness exercises, mindfulness based stress reduction (MBSR) and mindfulness based cognitive therapy (MBCT) have been shown to reduce distress in chronic pain and decrease risk of depression relapse. These standardized mindfulness (ST-Mindfulness) practices predominantly require attending to breath and body sensations. Here, we offer a novel view of ST-Mindfulness's somatic focus as a form of training for optimizing attentional modulation of 7-14 Hz alpha rhythms that play a key role in filtering inputs to primary sensory neocortex and organizing the flow of sensory information in the brain. In support of the framework, we describe our previous finding that ST-Mindfulness enhanced attentional regulation of alpha in primary somatosensory cortex (SI). The framework allows us to make several predictions. In chronic pain, we predict somatic attention in ST-Mindfulness "de-biases" alpha in SI, freeing up pain-focused attentional resources. In depression relapse, we predict ST-Mindfulness's somatic attention competes with internally focused rumination, as internally focused cognitive processes (including working memory) rely on alpha filtering of sensory input. Our computational model predicts ST-Mindfulness enhances top-down modulation of alpha by facilitating precise alterations in timing and efficacy of SI thalamocortical inputs. We conclude by considering how the framework aligns with Buddhist teachings that mindfulness starts with "mindfulness of the body." Translating this theory into neurophysiology, we hypothesize that with its somatic focus, mindfulness' top-down alpha rhythm modulation in SI enhances gain control which, in turn, sensitizes practitioners to better detect and regulate when the mind wanders from its somatic focus. This enhanced regulation of somatic mind-wandering may be an important early stage of mindfulness training that leads to enhanced cognitive regulation and metacognition.

Oscillatory alpha-band suppression mechanisms during the rapid attentional shifts required to perform an anti-saccade task

Neuroimaging has demonstrated anatomical overlap between covert and overt attention systems, although behavioral and electrophysiological studies have suggested that the two systems do not rely on entirely identical circuits or mechanisms. In a parallel line of research, topographically-specific modulations of alpha-band power (~8-14 Hz) have been consistently correlated with anticipatory states during tasks requiring covert attention shifts. These tasks, however, typically employ cue-target-interval paradigms where attentional processes are examined across relatively protracted periods of time and not at the rapid timescales implicated during overt attention tasks. The anti-saccade task, where one must first covertly attend for a peripheral target, before executing a rapid overt attention shift (i.e. a saccade) to the opposite side of space, is particularly well-suited for examining the rapid dynamics of overt attentional deployments. Here, we asked whether alpha-band oscillatory mechanisms would also be associated with these very rapid overt shifts, potentially representing a common neural mechanism across overt and covert attention systems. High-density electroencephalography in conjunction with infra-red eye-tracking was recorded while participants engaged in both pro- and anti-saccade task blocks. Alpha power, time-locked to saccade onset, showed three distinct phases of significantly lateralized topographic shifts, all occurring within a period of less than 1s, closely reflecting the temporal dynamics of anti-saccade performance. Only two such phases were observed during the pro-saccade task. These data point to substantially more rapid temporal dynamics of alpha-band suppressive mechanisms than previously established, and implicate oscillatory alpha-band activity as a common mechanism across both overt and covert attentional deployments.

Task-dependent modulation of SI physiological responses to targets and distractors

Selective attention experimental designs have shown that neural responses to stimuli in primary somatosensory cortex are stronger when the sensory stimuli are task relevant. Other studies have used animals under no task demands for data collection. The relationship between neural responses in the brain during behavior, and while an animal has no task demands, remains underexplored. We trained two animals to perform somatosensory detection for several weeks, followed by somatosensory discrimination for several weeks. Data in response to physically identical stimuli were collected from cortical implants while the animal was under no task demands before each behavioral session and also during that behavioral session. The Fourier spectra of the field potentials during detection or discrimination compared with the no task condition demonstrated suppression of the somatosensory μ-rhythm that is associated with readiness and anticipation of cognitive use of somatosensory and motor inputs. Responses to the task target were stronger during detection and discrimination than in the no task condition. The amplitude normalized time course of the target evoked response was similar in both cases. Evoked responses to the task distractor were not significantly stronger during behavior than in recordings under no task demands. The normalized time course of the distractor responses showed a suppression that peaks 30-35 ms after the onset of the response. The selectivity of this within trial suppression is the same as the selectivity of enduring suppression evident in studies of sensory cortical plasticity, which suggests the same neural process may be responsible for both.

The human somatosensory system: from perception to decision making

Pioneering human and animal research has yielded a better understanding of the brain networks involved in somatosensory perception and decision making. New methodical achievements in combination with computational formalization allow research questions to be addressed which increasingly reflect not only the complex sensory demands of real environments, but also the cognitive ones. Here, we review the latest research on somatosensory perception and decision making with a special focus on the recruitment of supplementary brain networks which are dependent on the situation-associated sensory and cognitive demands. We also refer to literature on sensory-motor integration processes during visual decision making to delineate the complexity and dynamics of how sensory information is relayed to the motor output system. Finally, we review the latest literature which provides novel evidence that other everyday life situations, such as semantic decision making or social interactions, appear to depend on tactile experiences; suggesting that the sense of touch, being the first sense to develop ontogenetically, may essentially support later development of other conceptual knowledge.

Attentional cues affect accuracy and reaction time via different cognitive and neural processes

We investigated whether symbolic endogenous attentional cues affect perceptual accuracy and reaction time (RT) via different cognitive and neural processes. We recorded magnetoencephalography in 19 humans while they performed a cued somatosensory discrimination task in which the cue-target interval was varied between 0 and 1000 ms. Comparing behavioral and neural measures, we show that (1) attentional cueing affects accuracy and RT with different time courses and (2) the time course of our neural measure (anticipatory suppression of neuronal oscillations in stimulus-receiving sensory cortex) only accounts for the accuracy time course. A model is proposed in which the effect on accuracy is explained by a single process (preparatory excitability increase in sensory cortex), whereas the effect on RT is explained by an additional process that is sensitive to cue-target compatibility (post-target comparison between expected and actual stimulus location). These data provide new insights into the mechanisms underlying behavioral consequences of attentional cueing.

Thalamic model of awake alpha oscillations and implications for stimulus processing

We describe a unique conductance-based model of awake thalamic alpha and some of its implications for function. The full model includes a model for a specialized class of high-threshold thalamocortical cells (HTC cells), which burst at the alpha frequency at depolarized membrane potentials (~-56 mV). Our model generates alpha activity when the actions of either muscarinic acetylcholine receptor (mAChR) or metabotropic glutamate receptor 1 (mGluR1) agonists on thalamic reticular (RE), thalamocortical (TC), and HTC cells are mimicked. In our model of mGluR1-induced alpha, TC cells are equally likely to fire during any phase of alpha, consistent with in vitro experiments. By contrast, in our model of mAChR-induced alpha, TC cells tend to fire either at the peak or the trough of alpha, depending on conditions. Our modeling suggests that low levels of mGluR1 activation on a background of mAChR agonists may be able to initiate alpha activity that biases TC cells to fire at certain phases of alpha, offering a pathway for cortical control. If we introduce a strong stimulus by increasing the frequency of excitatory postsynaptic potentials (EPSPs) to TC cells, an increase in alpha power is needed to mimic the level of phasing of TC cells observed in vivo. This increased alpha power reduces the probability that TC cells spike near the trough of alpha. We suggest that mAChR-induced alpha may contribute to grouping TC activity into discrete perceptual units for processing, whereas mGluR1-induced alpha may serve the purpose of blocking unwanted stimuli from reaching the cortex.

Intensive training induces longitudinal changes in meditation state-related EEG oscillatory activity

The capacity to focus one's attention for an extended period of time can be increased through training in contemplative practices. However, the cognitive processes engaged during meditation that support trait changes in cognition are not well characterized. We conducted a longitudinal wait-list controlled study of intensive meditation training. Retreat participants practiced focused attention (FA) meditation techniques for three months during an initial retreat. Wait-list participants later undertook formally identical training during a second retreat. Dense-array scalp-recorded electroencephalogram (EEG) data were collected during 6 min of mindfulness of breathing meditation at three assessment points during each retreat. Second-order blind source separation, along with a novel semi-automatic artifact removal tool (SMART), was used for data preprocessing. We observed replicable reductions in meditative state-related beta-band power bilaterally over anteriocentral and posterior scalp regions. In addition, individual alpha frequency (IAF) decreased across both retreats and in direct relation to the amount of meditative practice. These findings provide evidence for replicable longitudinal changes in brain oscillatory activity during meditation and increase our understanding of the cortical processes engaged during meditation that may support long-term improvements in cognition.

Intended actions and unexpected outcomes: automatic and controlled processing in a rapid motor task

Human action involves a combination of controlled and automatic behavior. These processes may interact in tasks requiring rapid response selection or inhibition, where temporal constraints preclude timely intervention by conscious, controlled processes over automatized prepotent responses. Such contexts tend to produce frequent errors, but also rapidly executed correct responses, both of which may sometimes be perceived as surprising, unintended, or “automatic”. In order to identify neural processes underlying these two aspects of cognitive control, we measured neuromagnetic brain activity in 12 right-handed subjects during manual responses to rapidly presented digits, with an infrequent target digit that required switching response hand (bimanual task) or response finger (unimanual task). Automaticity of responding was evidenced by response speeding (shorter response times) prior to both failed and fast correct switches. Consistent with this automaticity interpretation of fast correct switches, we observed bilateral motor preparation, as indexed by suppression of beta band (15–30 Hz) oscillations in motor cortex, prior to processing of the switch cue in the bimanual task. In contrast, right frontal theta activity (4–8 Hz) accompanying correct switch responses began after cue onset, suggesting that it reflected controlled inhibition of the default response. Further, this activity was reduced on fast correct switch trials suggesting a more automatic mode of inhibitory control. We also observed post-movement (event-related negativity) ERN-like responses and theta band increases in medial and anterior frontal regions that were significantly larger on error trials, and may reflect a combination of error and delayed inhibitory signals. We conclude that both automatic and controlled processes are engaged in parallel during rapid motor tasks, and that the relative strength and timing of these processes may underlie both optimal task performance and subjective experiences of automaticity or control.

Beyond establishing involvement: quantifying the contribution of anticipatory α- and β-band suppression to perceptual improvement with attention

Systems and cognitive neuroscience aim at understanding the neurophysiological mechanisms that underlie cognition and behavior. Many studies have revealed the involvement of many types of neural signals in diverse cognitive and behavioral phenomena. Here, we go beyond establishing such involvement and address two fundamental, yet largely unaddressed, questions: 1) exactly how much does a given neural signal contribute to a cognitive or behavioral phenomenon of interest; and 2) to what extent are distinct neural signals independently related to this phenomenon? We recorded brain activity using magnetoencephalography while human participants performed a cued somatosensory detection task. Using a novel method, we then quantified the contribution (in a predictive but not causal sense) of two well-established neural phenomena to the improvement in perception with attentional orienting. In our sample, the anticipatory suppression of extracranially recorded oscillatory α- and β-band amplitudes from contralateral primary somatosensory cortex could account for maximally 29% of the attention-induced improvement in tactile perception. In addition, although amplitude suppressions in the α- and β-frequency bands both contributed to this improvement, their contribution was largely shared. These data reveal the upper limit of the cognitive/behavioral relevance of this type of signal and show that at least 71% of the perceptual improvement with attention must be accounted for by other signals.

Pre- and post-stimulus alpha activity shows differential modulation with spatial attention during the processing of pain

Extensive work using magneto- and electroencephalography (M/EEG) suggests that cortical alpha activity represents a top-down controlled gating mechanism employed by processes like attention across different modalities. However, it is not yet clear to what extent this presumed gating function of alpha activity also applies to the processing of pain. In the current study, a spatial attention paradigm was employed requiring subjects to attend to painful laser stimuli on one hand while ignoring stimuli on the other hand. Simultaneously, brain activity was recorded with MEG. In order to disentangle pre- and post-stimulus effects of attention, alpha activity was analyzed during time windows in anticipation of and in response to painful laser stimulation. Painful laser stimuli led to a suppression of alpha activity over both ipsi- and contralateral primary somatosensory areas irrespective if they were attended or ignored. Spatial attention was associated with a lateralization of anticipatory pre-stimulus alpha activity. Alpha activity was lower over primary somatosensory areas when the contralateral hand was attended compared to when the ipsilateral hand was attended, in line with the notion that oscillatory alpha activity regulates the flow of incoming information by engaging and/or disengaging early sensory areas. On the contrary, post-stimulus alpha activity, for stimuli on either hand, was consistently decreased with attention over contralateral areas. Most likely, this finding reflects an increased cortical activation and enhanced alerting if a painful stimulus is attended. The present results show that spatial attention results in a modulation of both pre- and post-stimulus alpha activity associated with pain. This flexible regulation of alpha activity matches findings from other modalities. We conclude that the assumed functional role of alpha activity as a top-down controlled gating mechanism includes pain processing and most likely represents a unified mechanism used throughout the brain.

Repetitive tactile stimulation changes resting-state functional connectivity-implications for treatment of sensorimotor decline

Neurological disorders and physiological aging can lead to a decline of perceptual abilities. In contrast to the conventional therapeutic approach that comprises intensive training and practicing, passive repetitive sensory stimulation (RSS) has recently gained increasing attention as an alternative to countervail the sensory decline by improving perceptual abilities without the need of active participation. A particularly effective type of high-frequency RSS, utilizing Hebbian learning principles, improves perceptual acuity as well as sensorimotor functions and has been successfully applied to treat chronic stroke patients and elderly subjects. High-frequency RSS has been shown to induce plastic changes of somatosensory cortex such as representational map reorganization, but its impact on the brain's ongoing network activity and resting-state functional connectivity has not been investigated so far. Here, we applied high-frequency RSS in healthy human subjects and analyzed resting state Electroencephalography (EEG) functional connectivity patterns before and after RSS by means of imaginary coherency (ImCoh), a frequency-specific connectivity measure which is known to reduce over-estimation biases due to volume conduction and common reference. Thirty minutes of passive high-frequency RSS lead to significant ImCoh-changes of the resting state mu-rhythm in the individual upper alpha frequency band within distributed sensory and motor cortical areas. These stimulation induced distributed functional connectivity changes likely underlie the previously observed improvement in sensorimotor integration.

Enhancing non-noxious perception: behavioural and neurophysiological correlates of a placebo-like manipulation

Sensory perception can be influenced by cognitive functions like attention and expectation. An emblematic case of this is the placebo effect, where a reduction in pain perception can be obtained by inducing expectation of benefit following a treatment. The current study assessed the behavioural and brain activity correlates of a placebo procedure inducing an enhancement of non-noxious somatic sensation. An experimental group was verbally suggested and surreptitiously conditioned about the effect of an inert cream in enhancing tactile perception, while a control group was informed about the actual inefficacy of the cream. Both groups received non-noxious electric shocks activating A-Beta fibres on the right index finger, before and after application of the cream in the same site. The behavioural and neurophysiological effects of this procedure were measured by a numerical rating scale of subjective perception and by recording cortical and subcortical somatosensory-evoked potentials (SEPs). Although the intensity of stimulation was physically identical in the two sessions, the experimental group reported stronger tactile sensation after cream treatment than before. In parallel, the experimental group showed enhanced somatosensory cortical responses (N140, P200) after treatment, whereas subcortical and early-cortical SEP components did not change. We suggest that these findings reflect top-down modulation on tactile perception probably due to an interplay between expectation and attention and might rely on interactions between prefrontal and parietal brain regions.

Supramodal parametric working memory processing in humans

Previous studies of delayed-match-to-sample (DMTS) frequency discrimination in animals and humans have succeeded in delineating the neural signature of frequency processing in somatosensory working memory (WM). During retention of vibrotactile frequencies, stimulus-dependent single-cell and population activity in prefrontal cortex was found to reflect the task-relevant memory content, whereas increases in occipital alpha activity signaled the disengagement of areas not relevant for the tactile task. Here, we recorded EEG from human participants to determine the extent to which these mechanisms can be generalized to frequency retention in the visual and auditory domains. Subjects performed analogous variants of a DMTS frequency discrimination task, with the frequency information presented either visually, auditorily, or by vibrotactile stimulation. Examining oscillatory EEG activity during frequency retention, we found characteristic topographical distributions of alpha power over visual, auditory, and somatosensory cortices, indicating systematic patterns of inhibition and engagement of early sensory areas, depending on stimulus modality. The task-relevant frequency information, in contrast, was found to be represented in right prefrontal cortex, independent of presentation mode. In each of the three modality conditions, parametric modulations of prefrontal upper beta activity (20-30 Hz) emerged, in a very similar manner as recently found in vibrotactile tasks. Together, the findings corroborate a view of parametric WM as supramodal internal scaling of abstract quantity information and suggest strong relevance of previous evidence from vibrotactile work for a more general framework of quantity processing in human working memory.

Somatosensory Anticipatory Alpha Activity Increases to Suppress Distracting Input

Effective processing of sensory input in daily life requires attentional selection and amplification of relevant input and, just as importantly, attenuation of irrelevant information. It has been proposed that top–down modulation of oscillatory alpha band activity (8–14 Hz) serves to allocate resources to various regions, depending on task demands. In previous work, we showed that contralateral somatosensory alpha activity decreases to facilitate processing of an anticipated target stimulus in a tactile discrimination task. In the current study, we asked whether somatosensory alpha activity is also modulated when expecting incoming distracting stimuli on the nonattended side. We hypothesized that an ipsilateral increase of alpha to suppress distracters would be required for optimal task performance. We recorded magneto-encephalography while subjects performed a tactile stimulus discrimination task where a cue directed attention either to their left or right hand. Distracters were presented simultaneously to the unattended hand. We found that alpha power contralateral to the attended hand decreased, whereas ipsilateral alpha power increased. In addition, posterior alpha power showed a general increase. Importantly, these three alpha components all contributed to discrimination performance. This study further extends the notion that alpha band activity is involved in shaping the functional architecture of the working brain by determining the engagement and disengagement of specific regions: Contralateral alpha decreases to facilitate stimulus detection, whereas ipsilateral alpha increases when active suppression of distracters is required. Importantly, the ipsilateral alpha increase is crucial for optimal task performance.

Attentional selection of location and modality in vision and touch modulates low-frequency activity in associated sensory cortices

Selective attention allows us to focus on particular sensory modalities and locations. Relatively little is known about how attention to a sensory modality may relate to selection of other features, such as spatial location, in terms of brain oscillations, although it has been proposed that low-frequency modulation (α- and β-bands) may be key. Here, we investigated how attention to space (left or right) and attention to modality (vision or touch) affect ongoing low-frequency oscillatory brain activity over human sensory cortex. Magnetoencephalography was recorded while participants performed a visual or tactile task. In different blocks, touch or vision was task-relevant, whereas spatial attention was cued to the left or right on each trial. Attending to one or other modality suppressed α-oscillations over the corresponding sensory cortex. Spatial attention led to reduced α-oscillations over both sensorimotor and occipital cortex contralateral to the attended location in the cue-target interval, when either modality was task-relevant. Even modality-selective sensors also showed spatial-attention effects for both modalities. The visual and sensorimotor results were generally highly convergent, yet, although attention effects in occipital cortex were dominant in the α-band, in sensorimotor cortex, these were also clearly present in the β-band. These results extend previous findings that spatial attention can operate in a multimodal fashion and indicate that attention to space and modality both rely on similar mechanisms that modulate low-frequency oscillations.

α-Oscillations in the monkey sensorimotor network influence discrimination performance by rhythmical inhibition of neuronal spiking

Extensive work in humans using magneto- and electroencephalography strongly suggests that decreased oscillatory α-activity (8-14 Hz) facilitates processing in a given region, whereas increased α-activity serves to actively suppress irrelevant or interfering processing. However, little work has been done to understand how α-activity is linked to neuronal firing. Here, we simultaneously recorded local field potentials and spikes from somatosensory, premotor, and motor regions while a trained monkey performed a vibrotactile discrimination task. In the local field potentials we observed strong activity in the α-band, which decreased in the sensorimotor regions during the discrimination task. This α-power decrease predicted better discrimination performance. Furthermore, the α-oscillations demonstrated a rhythmic relation with the spiking, such that firing was highest at the trough of the α-cycle. Firing rates increased with a decrease in α-power. These findings suggest that α-oscillations exercise a strong inhibitory influence on both spike timing and firing rate. Thus, the pulsed inhibition by α-oscillations plays an important functional role in the extended sensorimotor system.

Fluctuations of prestimulus oscillatory power predict subjective perception of tactile simultaneity

Oscillatory activity is modulated by sensory stimulation but can also fluctuate in the absence of sensory input. Recent studies have demonstrated that such fluctuations of oscillatory activity can have substantial influence on the perception of subsequent stimuli. In the present study, we employed a simultaneity task in the somatosensory domain to study the role of prestimulus oscillatory activity on the temporal perception of 2 events. Subjects received electrical stimulations of the left and right index finger with varying stimulus onset asynchronies (SOAs) and reported their subjective perception of simultaneity, while brain activity was recorded with magnetoencephalography. With intermediate SOAs (30 and 45 ms), subjects frequently misperceived the stimulation as simultaneously. We compared neuronal oscillatory power in these conditions and found that power in the high beta band (∼20 to 40 Hz) in primary and secondary somatosensory cortex prior to the electrical stimulation predicted subjects' reports of simultaneity. Additionally, prestimulus alpha-band power influenced perception in the condition SOA 45 ms. Our results indicate that fluctuations of ongoing oscillatory activity in the beta and alpha bands shape subjective perception of physically identical stimulation.

Dynamics of dynamics within a single data acquisition session: variation in neocortical alpha oscillations in human MEG

BACKGROUND

Behavioral paradigms applied during human recordings in electro- and magneto- encephalography (EEG and MEG) typically require 1-2 hours of data collection. Over this time scale, the natural fluctuations in brain state or rapid learning effects could impact measured signals, but are seldom analyzed.

METHODS AND FINDINGS

We investigated within-session dynamics of neocortical alpha (7-14 Hz) rhythms and their allocation with cued-attention using MEG recorded from primary somatosensory neocortex (SI) in humans. We found that there were significant and systematic changes across a single ~1 hour recording session in several dimensions, including increased alpha power, increased differentiation in attention-induced alpha allocation, increased distinction in immediate time-locked post-cue evoked responses in SI to different visual cues, and enhanced power in the immediate cue-locked alpha band frequency response. Further, comparison of two commonly used baseline methods showed that conclusions on the evolution of alpha dynamics across a session were dependent on the normalization method used.

CONCLUSIONS

These findings are important not only as they relate to studies of oscillations in SI, they also provide a robust example of the type of dynamic changes in brain measures within a single session that are overlooked in most human brain imaging/recording studies.

Trained modulation of sensorimotor rhythms can affect reaction time

OBJECTIVE

Brain-computer interface (BCI) technology might be useful for rehabilitation of motor function. This speculation is based on the premise that modifying the EEG will modify behavior, a proposition for which there is limited empirical data. The present study examined the possibility that voluntary modulation of sensorimotor rhythm (SMR) can affect motor behavior in normal human subjects.

METHODS

Six individuals performed a cued-reaction task with variable warning periods. A typical variable foreperiod effect was associated with SMR desynchronization. SMR features that correlated with reaction times were then used to control a two-target cursor movement BCI task. Following successful BCI training, an uncued reaction time task was embedded within the cursor movement task.

RESULTS

Voluntarily increasing SMR beta rhythms was associated with longer reaction times than decreasing SMR beta rhythms.

CONCLUSIONS

Voluntary modulation of EEG SMR can affect motor behavior.

SIGNIFICANCE

These results encourage studies that integrate BCI training into rehabilitation protocols and examine its capacity to augment restoration of useful motor function.

Placebo acupuncture as a form of ritual touch healing: a neurophenomenological model

Evidence that placebo acupuncture is an effective treatment for chronic pain presents a puzzle: how do placebo needles appearing to patients to penetrate the body, but instead sitting on the skin's surface in the manner of a tactile stimulus, evoke a healing response? Previous accounts of ritual touch healing in which patients often described enhanced touch sensations (including warmth, tingling or flowing sensations) suggest an embodied healing mechanism. In this qualitative study, we asked a subset of patients in a singleblind randomized trial in irritable bowel syndrome to describe their treatment experiences while undergoing placebo treament. Analysis focused on patients' unprompted descriptions of any enhanced touch sensations (e.g., warmth, tingling) and any significance patients assigned to the sensations. We found in 5/6 cases, patients associated sensations including "warmth" and "tingling" with treatment efficacy. The conclusion offers a "neurophenomenological" account of the placebo effect by considering dynamic effects of attentional filtering on early sensory cortices, possibly underlying the phenomenology of placebo acupuncture.

The Role of Alpha-Band Brain Oscillations as a Sensory Suppression Mechanism during Selective Attention

Evidence has amassed from both animal intracranial recordings and human electrophysiology that neural oscillatory mechanisms play a critical role in a number of cognitive functions such as learning, memory, feature binding and sensory gating. The wide availability of high-density electrical and magnetic recordings (64-256 channels) over the past two decades has allowed for renewed efforts in the characterization and localization of these rhythms. A variety of cognitive effects that are associated with specific brain oscillations have been reported, which range in spectral, temporal, and spatial characteristics depending on the context. Our laboratory has focused on investigating the role of alpha-band oscillatory activity (8-14 Hz) as a potential attentional suppression mechanism, and this particular oscillatory attention mechanism will be the focus of the current review. We discuss findings in the context of intersensory selective attention as well as intrasensory spatial and feature-based attention in the visual, auditory, and tactile domains. The weight of evidence suggests that alpha-band oscillations can be actively invoked within cortical regions across multiple sensory systems, particularly when these regions are involved in processing irrelevant or distracting information. That is, a central role for alpha seems to be as an attentional suppression mechanism when objects or features need to be specifically ignored or selected against.

Effects of mindfulness meditation training on anticipatory alpha modulation in primary somatosensory cortex

During selective attention, ∼7-14 Hz alpha rhythms are modulated in early sensory cortices, suggesting a mechanistic role for these dynamics in perception. Here, we investigated whether alpha modulation can be enhanced by "mindfulness" meditation (MM), a program training practitioners in sustained attention to body and breath-related sensations. We hypothesized that participants in the MM group would exhibit enhanced alpha power modulation in a localized representation in the primary somatosensory neocortex in response to a cue, as compared to participants in the control group. Healthy subjects were randomized to 8-weeks of MM training or a control group. Using magnetoencephalographic (MEG) recording of the SI finger representation, we found meditators demonstrated enhanced alpha power modulation in response to a cue. This finding is the first to show enhanced local alpha modulation following sustained attentional training, and implicates this form of enhanced dynamic neural regulation in the behavioral effects of meditative practice.

Neuronal mechanisms and attentional modulation of corticothalamic α oscillations

Field potential oscillations in the ∼10 Hz range are known as the alpha rhythm. The genesis and function of alpha has been the subject of intense investigation for the past 80 years. Whereas early work focused on the thalamus as the pacemaker of alpha rhythm, subsequent slice studies revealed that pyramidal neurons in the deep layers of sensory cortices are capable of oscillating in the alpha frequency range independently. How thalamic and cortical generating mechanisms in the intact brain might interact to shape the organization and function of alpha oscillations remains unclear. We addressed this problem by analyzing laminar profiles of local field potential and multiunit activity (MUA) recorded with linear array multielectrodes from the striate cortex of two macaque monkeys performing an intermodal selective attention task. Current source density (CSD) analysis was combined with CSD-MUA coherence to identify intracortical alpha current generators and assess their potential for pacemaking. Coherence and Granger causality analysis was applied to delineate the patterns of interaction among different alpha current generators. We found that (1) separable alpha current generators are located in superficial, granular, and deep layers, with both layer 4C and deep layers containing primary local pacemaking generators, suggesting the involvement of the thalamocortical network, and (2) visual attention reduces the magnitude of alpha oscillations as well as the level of alpha interactions, consistent with numerous reports of occipital alpha reduction with visual attention in human EEG. There is also indication that alpha oscillations in the lateral geniculate cohere with those in V1.

Using brain-computer interfaces and brain-state dependent stimulation as tools in cognitive neuroscience

Large efforts are currently being made to develop and improve online analysis of brain activity which can be used, e.g., for brain-computer interfacing (BCI). A BCI allows a subject to control a device by willfully changing his/her own brain activity. BCI therefore holds the promise as a tool for aiding the disabled and for augmenting human performance. While technical developments obviously are important, we will here argue that new insight gained from cognitive neuroscience can be used to identify signatures of neural activation which reliably can be modulated by the subject at will. This review will focus mainly on oscillatory activity in the alpha band which is strongly modulated by changes in covert attention. Besides developing BCIs for their traditional purpose, they might also be used as a research tool for cognitive neuroscience. There is currently a strong interest in how brain-state fluctuations impact cognition. These state fluctuations are partly reflected by ongoing oscillatory activity. The functional role of the brain state can be investigated by introducing stimuli in real-time to subjects depending on the actual state of the brain. This principle of brain-state dependent stimulation may also be used as a practical tool for augmenting human behavior. In conclusion, new approaches based on online analysis of ongoing brain activity are currently in rapid development. These approaches are amongst others informed by new insight gained from electroencephalography/magnetoencephalography studies in cognitive neuroscience and hold the promise of providing new ways for investigating the brain at work.

Stimulus-dependent EEG activity reflects internal updating of tactile working memory in humans

Despite recent advances in uncovering the neural signature of tactile working memory processing in animals and humans, the representation of internally modified somatosensory working memory content has not been studied so far. Here, recording EEG in human participants (n = 25) performing a modified delayed match-to-sample task allowed us to disambiguate internally driven memory processing from encoding-related delay activity. After presentation of two distinct vibrotactile frequencies to different index fingers, a visual cue indicated which of the two previous stimuli had to be maintained in working memory throughout a retention interval for subsequent frequency discrimination against a probe stimulus. During cued stimulus maintenance, α activity (8-13 Hz) over early somatosensory cortices was lateralized according to the cued tactile stimulus, even though the location of the stimuli was task irrelevant. The task-relevant memory content, in contrast, was found to be represented in right prefrontal cortex. The key finding was that the visually presented instructions triggered systematic modulations of prefrontal β-band activity (20-25 Hz), which selectively reflected the to-be-maintained frequency of the cued tactile vibration. The results expand previous evidence for parametric representations of vibrotactile frequency in the prefrontal cortex and corroborate a central role of dynamic β-band synchronization during active processing of an analog stimulus quantity in human working memory. In particular, our findings suggest that such processing supports not only sustained maintenance but also purposeful modification and updating of the task-relevant working memory contents.

Top-down controlled alpha band activity in somatosensory areas determines behavioral performance in a discrimination task

The brain receives a rich flow of information which must be processed according to behavioral relevance. How is the state of the sensory system adjusted to up- or downregulate processing according to anticipation? We used magnetoencephalography to investigate whether prestimulus alpha band activity (8-14 Hz) reflects allocation of attentional resources in the human somatosensory system. Subjects performed a tactile discrimination task where a visual cue directed attention to their right or left hand. The strength of attentional modulation was controlled by varying the reliability of the cue in three experimental blocks (100%, 75%, or 50% valid cueing). While somatosensory prestimulus alpha power lateralized strongly with a fully predictive cue (100%), lateralization was decreased with lower cue reliability (75%) and virtually absent if the cue had no predictive value at all (50%). Importantly, alpha lateralization influenced the subjects' behavioral performance positively: both accuracy and speed of response improved with the degree of alpha lateralization. This study demonstrates that prestimulus alpha lateralization in the somatosensory system behaves similarly to posterior alpha activity observed in visual attention tasks. Our findings extend the notion that alpha band activity is involved in shaping the functional architecture of the working brain by determining both the engagement and disengagement of specific regions: the degree of anticipation modulates the alpha activity in sensory regions in a graded manner. Thus, the alpha activity is under top-down control and seems to play an important role for setting the state of sensory regions to optimize processing.

Orienting attention to an upcoming tactile event involves a spatially and temporally specific modulation of sensorimotor alpha- and beta-band oscillations

Our perception is facilitated if we know where and when a sensory stimulus will occur. This phenomenon is accounted for by spatial and temporal orienting of attention. Whereas spatial orienting of attention has repeatedly been shown to involve spatially specific modulations of ongoing oscillations within sensory cortex, it is not clear to what extent anticipatory modulations of ongoing oscillations are involved in temporal orienting of attention. To address this, we recorded magnetoencephalography while human participants performed a tactile discrimination task. We cued participants to the left or the right hand, after which a tactile stimulus was presented at one of several fixed temporal delays. We thus assessed whether and how ongoing sensorimotor oscillations are modulated during tactile anticipation. We provide evidence for three phenomena. First, orienting to an upcoming tactile event involves a spatially specific contralateral suppression of alpha- and beta-band oscillations within sensorimotor cortex. Second, this modulation is deployed with temporal specificity, and this is more pronounced for beta-band compared with alpha-band oscillations. Third, the contralateral suppression of beta-band oscillations is associated with faster responses to subsequently presented tactile stimuli. Control measures showed that these results cannot be explained by motor planning or execution. We conclude that the modulation of ongoing oscillations within sensory cortex reflects a unifying mechanism underlying both spatial and temporal orienting of attention.

Thalamocortical model for a propofol-induced alpha-rhythm associated with loss of consciousness

Recent data reveal that the general anesthetic propofol gives rise to a frontal α-rhythm at dose levels sufficient to induce loss of consciousness. In this work, a computational model is developed that suggests the network mechanisms responsible for such a rhythm. It is shown that propofol can alter the dynamics in thalamocortical loops, leading to persistent and synchronous α-activity. The synchrony that forms in the cortex by virtue of the involvement of the thalamus may impede responsiveness to external stimuli, thus providing a correlate for the unconscious state.