How the brain stays in sync with the real world

The brain can predict the location of a moving object to compensate for the delays caused by the processing of neural signals

Attention rhythmically samples multi-feature objects in working memory

Attention allows us to selectively enhance processing of specific locations or features in our external environment while filtering out irrelevant information. It is currently hypothesized that this is achieved through boosting of relevant sensory signals which biases the competition between neural representations. Recent neurophysiological and behavioral studies revealed that attention is a fundamentally rhythmic process, tightly linked to neural oscillations in frontoparietal networks. Instead of continuously highlighting a single object or location, attention rhythmically alternates between multiple relevant representations at a frequency of 3–8 Hz. However, attention cannot only be directed towards the external world but also towards internal visual working memory (VWM) representations, e.g. when selecting one of several search templates to find corresponding objects in the external world. Two recent studies demonstrate that single-feature objects in VWM are attended in a similar rhythmic fashion as perceived objects. Here we add to the literature by showing that non-spatial retro-cues initiate comparable theta-rhythmic sampling of multi-feature objects in VWM. Our findings add to the converging body of evidence that external and internal visual representations are accessed by similar rhythmic attentional mechanisms and present a potential solution to the binding problem in working memory

A matter of availability: sharper tuning for memorized than for perceived stimulus features

Our visual environment is relatively stable over time. An optimized visual system could capitalize on this by devoting less representational resources to objects that are physically present. The vividness of subjective experience, however, suggests that externally available (perceived) information is more strongly represented in neural signals than memorized information. To distinguish between these opposing predictions, we use EEG multivariate pattern analysis to quantify the representational strength of task-relevant features in anticipation of a change-detection task. Perceptual availability was manipulated between experimental blocks by either keeping the stimulus available on the screen during a 2-s delay period (perception) or removing it shortly after its initial presentation (memory). We find that task-relevant (attended) memorized features are more strongly represented than irrelevant (unattended) features. More importantly, we find that task-relevant features evoke significantly weaker representations when they are perceptually available compared with when they are unavailable. These findings demonstrate that, contrary to what subjective experience suggests, vividly perceived stimuli elicit weaker neural representations (in terms of detectable multivariate information) than the same stimuli maintained in visual working memory. We hypothesize that an efficient visual system spends little of its limited resources on the internal representation of information that is externally available anyway

Étude de la relation causale entre les oscillations cérébrales et la perception en utilisant des techniques non invasives de stimulation cérébrale

It should have become clear now that oscillatory activity has profound effects on multiple aspects of our perception and is strongly involved in the way we sample our visual environment. Many of these relationships however are poorly understood, specifically in their causal-directional nature. In this thesis, I investigate the causal role of neural oscillations in temporal sampling mechanisms. The original manuscripts in chapter II and III are dedicated to perceptual sampling in the alpha band. It is hypothesized that this form of sampling has effects on time perception in our visual system. We tested this by manipulating alpha oscillations with rhythmic stimulation while observing changes in perceived relative timing of visual stimuli. Besides behavioral oscillations there are also neural signatures that hint at the intrinsic periodicity with which sensory cortices collect information. The oscillatory nature of perceptual echoes strongly implies that the visual system selectively reverbrates the 10 Hz component of its input. If we could extend these perceptual echoes to other modalities we would have evidence that 1. these other modalities also process information periodically and 2. that they utilize similar neural mechanisms for this purpose. In the original manuscripts in chapter IV I investigated if we can find perceptual echoes in the tactile domain. The periodic sampling mechanisms of the brain seem to be dissociable into a more low-level perceptual and a more high-level attentional sampling mechanism. Attentional sampling is assumed to be more flexible, task dependent and has recently been hypothesized to be caused by theta rhythmic activity in macaques. Providing support for these findings in humans would help us to identify the oscillatory mechanism that is responsible for behavioral attentional fluctuations found in many studies. The original manuscript in chapter V presents a study in which we replicate behavioral findings of the macaque-study in humans. Which location in the visual field attentional sampling mechanisms can collect information from depends entirely on the position of our eyes. Saccades and attentional sampling need therefore be highly coordinated. One way to synchronize these two systems is through oscillatory activity. It has been proposed that saccades, and surprisingly also strong visual transients, can reset the phase of theta oscillations which in turn allow for well timed processing of relevant stimuli. If this mechanism indeed relies on rhythmic activity then we should be able to disrupt it and observe corresponding errors in attentional sampling. The original manuscript in chapter VI investigates which effects strong visual disruptions have on the perceived relative timing of two stimuli. During my doctorate I sought to answer the following research questions: 1. Is the occipital alpha rhythm causally involved in discretely sampling visual information? (chapter II and III) 2. Is there a link between oscillatory activity and rhythmic sampling in the somatosensory system? (chapter IV) 3. Can we manipulate theta rhythmic activity to modulate attentional sampling? (chapter V and VI)Dans cette thèse, j'étudie le rôle causal des oscillations neurales dans les mécanismes d'échantillonnage temporel. Les manuscrits originaux des chapitres II et III sont consacrés à l'échantillonnage perceptuel dans la bande alpha. L'hypothèse est que cette forme d'échantillonnage a des effets sur la perception du temps dans notre système visuel. Nous l'avons testé en manipulant des oscillations alpha avec une stimulation rythmique tout en observant des changements dans la perception du temps relatif des stimuli visuels. Outre les oscillations comportementales, il existe également des signatures neurales qui font allusion à la périodicité intrinsèque avec laquelle les cortex sensoriels collectent les informations. La nature oscillatoire des échos perceptifs implique fortement que le système visuel réverbère sélectivement la composante 10 Hz de son entrée. Si nous pouvions étendre ces échos perceptuels à d'autres modalités, nous aurions la preuve que ces modalités collectent également des informations de façon périodique et qu'elles utilisent des mécanismes similaires pour ce faire. Dans les manuscrits originaux du chapitre IV, j'ai cherché à savoir si nous pouvons trouver des échos perceptuels dans le domaine tactile. Les mécanismes d'échantillonnage périodique du cerveau semblent pouvoir être dissociés en un mécanisme d'échantillonnage perceptif de bas niveau et un mécanisme d'échantillonnage attentionnel de haut niveau. L'échantillonnage attentionnel est supposé être plus flexible et dépendant de la tâche et il a récemment été démontré qu'il est causé par l'activité rythmique thêta chez les macaques. La confirmation de ces résultats chez l'homme nous aiderait à identifier le mécanisme oscillatoire responsable des fluctuations de l'attention. Le manuscrit original du chapitre V présente une étude dans laquelle nous reproduisons les résultats comportementaux de l'étude sur les macaques chez les humains. L'endroit du champ visuel à partir duquel les mécanismes d'échantillonnage de l'attention peuvent recueillir des informations dépend entièrement de la position de nos yeux. Les saccades et les fluctuations de l'attention doivent donc être hautement coordonnées. Une façon de synchroniser ces deux systèmes est l'activité oscillatoire. Il a été proposé que les saccades et les fortes transitions visuelles remettent à zéro la phase des oscillations thêta, ce qui permet de traiter les stimuli pertinents en temps voulu. Si ce mécanisme repose effectivement sur une activité rythmique, nous devrions pouvoir la perturber et observer les erreurs correspondantes dans l'échantillonnage attentionnel.[...

The causal role of neural oscillations in attentional and perceptual sampling mechanisms

Dans cette thèse, j'étudie le rôle causal des oscillations neurales dans les mécanismes d'échantillonnage temporel. Les manuscrits originaux des chapitres II et III sont consacrés à l'échantillonnage perceptuel dans la bande alpha. L'hypothèse est que cette forme d'échantillonnage a des effets sur la perception du temps dans notre système visuel. Nous l'avons testé en manipulant des oscillations alpha avec une stimulation rythmique tout en observant des changements dans la perception du temps relatif des stimuli visuels. Outre les oscillations comportementales, il existe également des signatures neurales qui font allusion à la périodicité intrinsèque avec laquelle les cortex sensoriels collectent les informations. La nature oscillatoire des échos perceptifs implique fortement que le système visuel réverbère sélectivement la composante 10 Hz de son entrée. Si nous pouvions étendre ces échos perceptuels à d'autres modalités, nous aurions la preuve que ces modalités collectent également des informations de façon périodique et qu'elles utilisent des mécanismes similaires pour ce faire. Dans les manuscrits originaux du chapitre IV, j'ai cherché à savoir si nous pouvons trouver des échos perceptuels dans le domaine tactile. Les mécanismes d'échantillonnage périodique du cerveau semblent pouvoir être dissociés en un mécanisme d'échantillonnage perceptif de bas niveau et un mécanisme d'échantillonnage attentionnel de haut niveau. L'échantillonnage attentionnel est supposé être plus flexible et dépendant de la tâche et il a récemment été démontré qu'il est causé par l'activité rythmique thêta chez les macaques. La confirmation de ces résultats chez l'homme nous aiderait à identifier le mécanisme oscillatoire responsable des fluctuations de l'attention. Le manuscrit original du chapitre V présente une étude dans laquelle nous reproduisons les résultats comportementaux de l'étude sur les macaques chez les humains. L'endroit du champ visuel à partir duquel les mécanismes d'échantillonnage de l'attention peuvent recueillir des informations dépend entièrement de la position de nos yeux. Les saccades et les fluctuations de l'attention doivent donc être hautement coordonnées. Une façon de synchroniser ces deux systèmes est l'activité oscillatoire. Il a été proposé que les saccades et les fortes transitions visuelles remettent à zéro la phase des oscillations thêta, ce qui permet de traiter les stimuli pertinents en temps voulu. Si ce mécanisme repose effectivement sur une activité rythmique, nous devrions pouvoir la perturber et observer les erreurs correspondantes dans l'échantillonnage attentionnel.[...]It should have become clear now that oscillatory activity has profound effects on multiple aspects of our perception and is strongly involved in the way we sample our visual environment. Many of these relationships however are poorly understood, specifically in their causal-directional nature. In this thesis, I investigate the causal role of neural oscillations in temporal sampling mechanisms. The original manuscripts in chapter II and III are dedicated to perceptual sampling in the alpha band. It is hypothesized that this form of sampling has effects on time perception in our visual system. We tested this by manipulating alpha oscillations with rhythmic stimulation while observing changes in perceived relative timing of visual stimuli. Besides behavioral oscillations there are also neural signatures that hint at the intrinsic periodicity with which sensory cortices collect information. The oscillatory nature of perceptual echoes strongly implies that the visual system selectively reverbrates the 10 Hz component of its input. If we could extend these perceptual echoes to other modalities we would have evidence that 1. these other modalities also process information periodically and 2. that they utilize similar neural mechanisms for this purpose. In the original manuscripts in chapter IV I investigated if we can find perceptual echoes in the tactile domain. The periodic sampling mechanisms of the brain seem to be dissociable into a more low-level perceptual and a more high-level attentional sampling mechanism. Attentional sampling is assumed to be more flexible, task dependent and has recently been hypothesized to be caused by theta rhythmic activity in macaques. Providing support for these findings in humans would help us to identify the oscillatory mechanism that is responsible for behavioral attentional fluctuations found in many studies. The original manuscript in chapter V presents a study in which we replicate behavioral findings of the macaque-study in humans. Which location in the visual field attentional sampling mechanisms can collect information from depends entirely on the position of our eyes. Saccades and attentional sampling need therefore be highly coordinated. One way to synchronize these two systems is through oscillatory activity. It has been proposed that saccades, and surprisingly also strong visual transients, can reset the phase of theta oscillations which in turn allow for well timed processing of relevant stimuli. If this mechanism indeed relies on rhythmic activity then we should be able to disrupt it and observe corresponding errors in attentional sampling. The original manuscript in chapter VI investigates which effects strong visual disruptions have on the perceived relative timing of two stimuli. During my doctorate I sought to answer the following research questions: 1. Is the occipital alpha rhythm causally involved in discretely sampling visual information? (chapter II and III) 2. Is there a link between oscillatory activity and rhythmic sampling in the somatosensory system? (chapter IV) 3. Can we manipulate theta rhythmic activity to modulate attentional sampling? (chapter V and VI

Random Tactile Noise Stimulation Reveals Beta-Rhythmic Impulse Response Function of the Somatosensory System

Both passive tactile stimulation and motor actions result in dynamic changes in beta band (15-30 Hz Hz) oscillations over somatosensory cortex. Similar to alpha band (8-12 Hz) power decrease in the visual system, beta band power also decreases following stimulation of the somatosensory system. This relative suppression of α and β oscillations is generally interpreted as an increase in cortical excitability. Here, next to traditional single-pulse stimuli, we employed a random intensity continuous right index finger tactile stimulation (white noise), which enabled us to uncover an impulse response function (IRF) of the somatosensory system. Contrary to previous findings, we demonstrate a burst-like initial increase rather than decrease of beta activity following white noise stimulation (human participants, N = 18, 8 female). These β bursts, on average, lasted for three cycles and their frequency was correlated with resonant frequency of somatosensory cortex, as measured by a multi-frequency steady-state somatosensory evoked potential (SSSEP) paradigm. Furthermore, beta band bursts shared spectro-temporal characteristics with evoked and resting-state β oscillations. Taken together, our findings not only reveal a novel oscillatory signature of somatosensory processing that mimics the previously reported visual IRFs, but also point to a common oscillatory generator underlying spontaneous β bursts in the absence of tactile stimulation and phase-locked β bursts following stimulation, the frequency of which is determined by the resonance properties of the somatosensory system.SIGNIFICANCE STATEMENTThe investigation of the transient nature of oscillations has gained great popularity in recent years. The findings of bursting activity rather than sustained oscillations in the beta band has provided important insights into its role in movement planning, working memory, inhibition and reactivation of neural ensembles. In this study, we show that also in response to tactile stimulation the somatosensory system responds with ∼3 cycle oscillatory beta band bursts, whose spectro-temporal characteristics are shared with evoked and resting-state beta band oscillatory signatures of the somatosensory system. As similar bursts have been observed in the visual domain, these oscillatory signatures might reflect an important supramodal mechanism in sensory processing

Occipital Alpha-TMS causally modulates Temporal Order Judgements: Evidence for discrete temporal windows in vision

International audienceRecent advances in neuroscience have challenged the view of conscious visual perception as a continuous process. Behavioral performance, reaction times and some visual illusions all undergo periodic fluctuations that can be traced back to oscillatory activity in the brain. These findings have given rise to the idea of a discrete sampling mechanism in the visual system. In this study we seek to investigate the causal relationship between occipital alpha oscillations and Temporal Order Judgements using neural entrainment via rhythmic TMS in 18 human subjects (9 females). We find that certain phases of the entrained oscillation facilitate temporal order perception of two visual stimuli, whereas others hinder it. Our findings support the idea that the visual system periodically compresses information into discrete packages within which temporal order information is lost

Dynamic and flexible transformation and reallocation of visual working memory representations

In their recent review, Xu critically assesses the role of early visual areas in VWM storage in the light of new fMRI-decoding studies that seemingly support the sensory storage account. We would like to extend the discussion by highlighting recent findings which suggest that early visual areas can dynamically transform active VWM representations e.g., to activity silent or long-term memory representations. These latent codes evade detection via traditional paradigms as well as decoding methods and hence limit the conclusions that can be drawn about the role of certain brain regions in WM storage. More precisely we claim that a lack or a temporary disappearance of multivariate VWM evidence from early visual brain regions does not imply that these areas are not essentially required to store and maintain active, or currently attended, VWM representations

Dynamic and flexible transformation and reallocation of visual working memory representations

In their recent review, Xu critically assesses the role of early visual areas in VWM storage in the light of new fMRI-decoding studies that seemingly support the sensory storage account. We would like to extend the discussion by highlighting recent findings which suggest that early visual areas can dynamically transform active VWM representations e.g., to activity silent or long-term memory representations. These latent codes evade detection via traditional paradigms as well as decoding methods and hence limit the conclusions that can be drawn about the role of certain brain regions in WM storage. More precisely we claim that a lack or a temporary disappearance of multivariate VWM evidence from early visual brain regions does not imply that these areas are not essentially required to store and maintain active, or currently attended, VWM representations