Program

Download SAMBA 2017 Program

Program

To the abstracts of the talks.

Time13.07.1714.07.17
08:30Registration & coffee
09:15Opening remarks
09:30Talk: Catherine Tallon-Baudry

Visceral inputs, brain dynamics and subjectivity
Talk: Pascal Fries

Rhythms for Cognition: Communication through Coherence
10:00
10:30CoffeeCoffee
11:00Talk: Christian-G. Bénar

Brain mapping at two scales: simultaneous recordings of MEG and intracerebral EEG
Talk: Tobias Donner

Distinct Catecholaminergic and Cholinergic Shaping of Large-scale Cortical Population Dynamics
11:30
12:00LunchLunch
12:30
13:00
13:30Talk: Jan Mathijs Schoffelen

How (not) to study directed interactions in brain networks using MEG
Talk: Angelika Lingnau

The organization of actions in the human brain
14:30
14:45Talk: Anne-Lise Giraud

The spatio-temporal geometry of speech processing
Talk: Rosalyn J. Moran

Probing Predictive Models in the Mind with Dynamic Causal Modeling
15:15
15:45Coffee & Poster Session 1 Coffee & Poster Session 2
16:15
17:00Talk: Paul Sauseng

Coordinating distributed cortical activity: significance of prefrontal slow(ish) brain oscillations
Talk: Sylvain Baillet

Mechanisms & dynamical structure of brain rhythms: from rest to perception
17:30
18:00Closing Remarks & Poster Awards

Abstracts

Baillet, Sylvain
Bénar, Christian-G.
Donner, Tobias
Fries, Pascal
Giraud, Anne-Lise
Lingnau, Angelika
Moran, Rosalyn
Sauseng, Paul
Schoffelen, Jan Mathijs
Tallon-Baudry, Catherine


Mechanisms & dynamical structure of brain rhythms: from rest to perception

Sylvain Baillet

McGill University, Montreal, Canada

One broad objective in neuroscience is to comprehend the mechanisms of large-scale, oscillatory neural dynamics: how they enable functions by shaping communication in brain networks, and how the earliest detection of their alterations in disease can contribute to improved healthcare prevention and interventions. We will review how the ubiquitous polyrhythmic activity of the brain has been approached empirically so far, with underlying mechanisms that remain not understood. This hinders our comprehension of how 1) perception and behaviour emerge from brain network activity, and 2) the pathophysiological developments of brain and mental-health disorders increasingly studied as network diseases, affect large-scale neural communication.
In this lecture, we will introduce how these difficult questions can benefit from a bottom-up approach: We aim to understand how basic physiological factors of neural integrity and function shape the dynamical structure of oscillatory brain rhythms, such as their interdependence across multiple frequencies through cross-frequency coupling. These phenomena represent a deep source of uncharted markers of neural excitability, activity and connectivity. I will illustrate these principles with our latest results concerning the resting brain, multimodal perception and pathophysiological markers of epilepsy and neurodegenerative syndromes.


Brain mapping at two scales: simultaneous recordings of MEG and intracerebral EEG.

Christian-G. Bénar

Institut de Neurosciences des Systèmes, Aix-Marseille Université, Marseille, France

Intracerebral EEG (stereotaxic EEG, SEEG), performed in patients during presurgical evaluation of epilepsy, provides a formidable opportunity for recording directly from brain structures in humans. From a neuroscientific point of view, this allows investigating brain networks at a mesoscopic scale, with high spatial precision and time-frequency sensitivity. From a methodological perspective, this provides a “ground truth” to which non-invasive results (EEG, MEG) can be compared. Several studies have thus validated non-invasive measures thanks to SEEG. This was however mostly performed on separate recordings, which is not optimal as brain activity fluctuates in time. The only way to ensure that the exact same activity is recorded at the two levels is thus to perform simultaneous recordings.

We performed simultaneous MEG-SEEG or EEG-MEG-SEEG recordings in as series of patients. I will present the technical challenges associated with such set-ups. I will show initial results on the detection of deep structures (amygdala, hippocampus) on MEG signals, as well as brain mapping application as a “meta modality” providing both a local and a global view on brain networks. Implications for computational modelling, methodological investigations and basic neuroscience will be discussed.


Distinct Catecholaminergic and Cholinergic Shaping of Large-scale Cortical Population Dynamics

Tobias H. Donner

University Medical Center Hamburg-Eppendorf, Hamburg, Germany

The dopaminergic, noradrenergic, and cholinergic systems have long been implicated in the regulation of behavioral state. The brainstem centers of these neuromodulatory systems receive top-down projections from frontal cortex and send widespread projections to large parts of the brain. Despite this similar organization, influential models postulate distinct computational roles for these systems in the orchestration of cognition and behavior. Yet, direct evidence for dissociated effects on their downstream targets is missing.

I will present physiological evidence for distinct roles of catecholamines (dopamine and noradrenaline) and acetylcholine in shaping the intrinsic dynamics of large-scale cortical population activity and cognition. We manipulated the levels of these neuromodulators with selective pharmacological interventions in humans and measured the resulting changes in the temporal and spatial correlation structure of intrinsic fluctuations in MEG activity. To this end, we compared two steady-state tasks differing in external drive: (i) blank fixation and (ii) silent counting of the alternations of perception of a continuously presented visual stimulus (3D structure-from-motion).

Catecholamines, but not acetylcholine, increased both, the rate of perceptual alternations, as well as the long-range temporal correlation structure alpha-band activity in parietal and occipital cortex. Computational modeling showed that both effects could be accounted for by a net increase in the ratio between excitation and inhibition in cortex. At the same time, catecholamines increased cortex-wide correlations in the low beta-band during task, whereas acetylcholine decreased these correlations, but during rest.

Our results reveal novel dissociations between the large-scale functional effects of key neuromodulatory systems, and set the stage for disentangling these systems’ computational roles.


Rhythms for Cognition: Communication through Coherence

Pascal Fries

Ernst Strüngmann Institute (ESI) for Neuroscience in Cooperation with Max Planck Society, Frankfurt, Germany

I will show that free viewing induces gamma-band oscillations in early visual cortex. If the gamma rhythm in a lower visual area entrains a gamma rhythm in a higher visual area, this might establish an effective communication protocol: The lower area sends a representation of the visual stimulus rhythmically, and the higher area is most excitable precisely when this representation arrives. At other times, the higher area is inhibited, which excludes competing stimuli. I refer to this scenario as the Communication-through-Coherence (CTC) hypothesis. I will show that the gamma rhythm in awake macaque V4 modulates the gain of synaptic inputs. I will further show that constant optogenetic stimulation in anesthetized cat area 21a (homologue to V4) induces a local gamma rhythm, and that this isolated gamma is sufficient to produce similar gain modulation. These gain modulation effects would be ideal to lend enhanced effective connectivity to attended stimuli. I will show that this is indeed the case between macaque V1 and V4. When two visual stimuli induce two local gamma rhythms in V1, only the one induced by the attended stimulus entrains V4. I will then investigate how these changes in gamma synchronization between visual areas are controlled by influences from parietal cortex. I will show that posterior parietal cortex influences visual areas primarily via beta-band synchronization. I will show that generally, beta-band influences are stronger in the top-down direction, while gamma-band influences are stronger in the bottom-up direction. This holds across macaques and human subjects, and in both species it allows building a hierarchy of visual areas based on the directed influences. Finally, I will show that attentional selection occurs at a theta rhythm. When two objects are monitored simultaneously, attentional benefits alternate at 4 Hz, consistent with an 8 Hz sampling rhythm, sampling them in alternation.


The spatio-temporal geometry of speech processing

Anne-Lise Giraud

University of Geneva, Switzerland

A review of a series of recent studies that critically explore different principles of neural coding in speech processing both theoretically with computational models and experimentally with MEG, fMRI and intracortical EEG recordings.


The organization of actions in the human brain

Angelika Lingnau

Royal Holloway University of London, UK
Center for Mind/ Brain Sciences, University of Trento, Italy

Being able to understand other people’s actions is fundamental for social interacions. One important problem our brain needs to resolve to achieve this task is to distinguish between different actions while generalizing across the way these actions are performed. In this talk I will present a number of recent studies using multivarite pattern analysis (MVPA) and representational similarity analysis (RSA) of functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) data to identify action representations that show generalization across effectors, kinematics and objects. I will discuss the results, which highlight the importance of the lateral occipito-temporal cortex for such abstract representations, in light of the ongoing debates on the neural basis of action understanding.


Probing Predictive Models in the Mind with Dynamic Causal Modeling

Rosalyn J Moran

University of Bristol, UK

Prediction and predictive codes are now ubiquitous computational viewpoints from which we may better understand neural circuit organization and signal transmission in the brain.

In this talk I will present a predictive view of changing brains, over lifespans, based on the Free Energy Principle, a theory of hierarchical empirical Bayesian inference in the brain (Friston 2013). This particular formulation of the Bayesian brain produces predictive coding schemes that have been used to inform the principles of perception, action and decision-making, accounting for how sensory information combines with our own prior beliefs about the world to shape brain activity and behavior. There are many ways that a brain could perform Bayesian inference and the hypothesized scheme under the Free Energy Principle in the perceptual domain posits a variational algorithm where posterior density estimation is recast as an optimization problem. In this guise the scheme becomes a predictive coding algorithm, with hierarchical structure and attribution of optimization dynamics to particular components of neuronal circuits.

In this talk I will present evidence from neuroimaging studies of brain circuits (using dynamic causal models) that age-related connectivity changes are commensurate with long-term Free-Energy minimization. I will present work from sensory learning, memory and decision making paradigms that show that the neurobiological implementations of prior beliefs grow stronger in older brains. I will explore how this relates to faster timescales of prediction in terms of electrophysiological correlates.


Coordinating distributed cortical activity: significance of prefrontal slow(ish) brain oscillations

Paul Sauseng

Department of Psychology, Ludwig-Maximilian-University Munich, Germany

Depending on which kind of information needs to be retained in working memory, and dependent on what exact mental transformation this information has to undergo, different working memory sub-processes will be necessary. These sub-processes are supposed to be implemented within different cortical networks. But how are these networks coordinated? How is communication in one reinforced and coupling of another one reduced depending on the task-requirements? Here I will provide a theoretical framework and empirical data arguing that slow brain oscillations in the prefrontal cortex – and specifically their phase to which fast frequency brain activity is locked – allow a simple and efficient mechanism by which fronto-parietal brain networks can be dynamically coupled or desynchronized, and hence, working memory processes can be coordinated. Electroencephalographic and combined EEG and non-invasive brain stimulation data from healthy participants, elderly volunteers and psychiatric patients will be presented.


How (not) to study directed interactions in brain networks using MEG

Jan-Mathijs Schoffelen

Radboud University, Nijmegen, Netherlands

Recent years have witnessed a rapid development of advanced signal processing techniques to explore dynamic interactions between brain regions using MEG-recordings. Also, the availability of state-of-the-art tools in open source data visualization and analysis packages (e.g. AnyWave, Brainstorm, SPM, Fieldtrip) has enabled researchers in the wider community to interrogate their data with connectivity-colored glasses. This in itself is a good thing, because studying the dynamics of connectivity is the way to go if we want to explore the coordinated interplay between brain regions that underlies perception, cognition and behavior. Yet, in order to get a good interpretation of the data, one needs to be aware of the limitations of the analysis techniques. In this talk, I will discuss my view on how directed interactions can be studied, and somewhat meaningfully interpreted. As an illustration, I will show some recent results showing frequency-specific directed interactions in the human brain network for language.


Visceral inputs, brain dynamics and subjectivity

Catherine Tallon-Baudry

Ecole Normale Supérieure Paris, France

Visceral organs such as the heart and the stomach constantly send information up to the cortex, thus potentially constraining brain dynamics. In addition, the brain might use visceral inputs to create a subject-centered reference frame, from which the first person perspective inherent to consciousness can develop. I will present recent evidence, gathered using MEG but also unit recordings and fMRI, that visceral inputs shape brain dynamics and contribute to subjective experience.