Bernstein Center for Computational Neuroscience

Berlin, Germany

Bernstein Center for Computational Neuroscience

Berlin, Germany
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Cichy R.M.,Massachusetts Institute of Technology | Ramirez F.M.,Bernstein Center for Computational Neuroscience | Pantazis D.,Massachusetts Institute of Technology
NeuroImage | Year: 2015

It is a principal open question whether noninvasive imaging methods in humans can decode information encoded at a spatial scale as fine as the basic functional unit of cortex: cortical columns. We addressed this question in five magnetoencephalography (MEG) experiments by investigating a columnar-level encoded visual feature: contrast edge orientation. We found that MEG signals contained orientation-specific information as early as approximately 50. ms after stimulus onset even when controlling for confounds, such as overrepresentation of particular orientations, stimulus edge interactions, and global form-related signals. Theoretical modeling confirmed the plausibility of this empirical result. An essential consequence of our results is that information encoded in the human brain at the level of cortical columns should in general be accessible by multivariate analysis of electrophysiological signals. © 2015 Elsevier Inc.

Haufe S.,TU Berlin | Nikulin V.V.,Franklin University | Nikulin V.V.,Bernstein Center for Computational Neuroscience | Muller K.-R.,TU Berlin | And 2 more authors.
NeuroImage | Year: 2013

Information flow between brain areas is difficult to estimate from EEG measurements due to the presence of noise as well as due to volume conduction. We here test the ability of popular measures of effective connectivity to detect an underlying neuronal interaction from simulated EEG data, as well as the ability of commonly used inverse source reconstruction techniques to improve the connectivity estimation. We find that volume conduction severely limits the neurophysiological interpretability of sensor-space connectivity analyses. Moreover, it may generally lead to conflicting results depending on the connectivity measure and statistical testing approach used. In particular, we note that the application of Granger-causal (GC) measures combined with standard significance testing leads to the detection of spurious connectivity regardless of whether the analysis is performed on sensor-space data or on sources estimated using three different established inverse methods. This empirical result follows from the definition of GC. The phase-slope index (PSI) does not suffer from this theoretical limitation and therefore performs well on our simulated data.We develop a theoretical framework to characterize artifacts of volume conduction, which may still be present even in reconstructed source time series as zero-lag correlations, and to distinguish their time-delayed brain interaction. Based on this theory we derive a procedure which suppresses the influence of volume conduction, but preserves effects related to time-lagged brain interaction in connectivity estimates. This is achieved by using time-reversed data as surrogates for statistical testing. We demonstrate that this robustification makes Granger-causal connectivity measures applicable to EEG data, achieving similar results as PSI. Integrating the insights of our study, we provide a guidance for measuring brain interaction from EEG data. Software for generating benchmark data is made available. © 2012 Elsevier Inc.

Hesselmann G.,Weizmann Institute of Science | Hebart M.,Bernstein Center for Computational Neuroscience | Malach R.,Weizmann Institute of Science
Journal of Neuroscience | Year: 2011

The study of conscious visual perception invariably necessitates some means of report. Report can be either subjective, i.e., an introspective evaluation of conscious experience, or objective, i.e., a forced-choice discrimination regarding different stimulus states. However, the link between report type and fMRI-BOLD signals has remained unknown. Here we used continuous flash suppression to render target images invisible, and observed a long-lasting dissociation between subjective report of visibility and human subjects' forced-choice localization of targets ("blindsight"). Our results show a robust dissociation between brain regions and type of report.Wefind subjective visibility effects in high-order visual areas even under equal objective performance. No significant BOLD difference was found between correct and incorrect trials in these areas when subjective report was constant.Onthe other hand, objective performance was linked to the accuracy of multivariate pattern classification mainly in early visual areas. Together, our data support the notion that subjective and objective reports tap cortical signals of different location and amplitude within the visual cortex. © 2011 the authors.

Einevoll G.T.,Norwegian University of Life Sciences | Kayser C.,University of Glasgow | Kayser C.,Bernstein Center for Computational Neuroscience | Logothetis N.K.,Max Planck Institute for Biological Cybernetics | And 3 more authors.
Nature Reviews Neuroscience | Year: 2013

The past decade has witnessed a renewed interest in cortical local field potentials (LFPs)-that is, extracellularly recorded potentials with frequencies of up to ~500 Hz. This is due to both the advent of multielectrodes, which has enabled recording of LFPs at tens to hundreds of sites simultaneously, and the insight that LFPs offer a unique window into key integrative synaptic processes in cortical populations. However, owing to its numerous potential neural sources, the LFP is more difficult to interpret than are spikes. Careful mathematical modelling and analysis are needed to take full advantage of the opportunities that this signal offers in understanding signal processing in cortical circuits and, ultimately, the neural basis of perception and cognition. © 2013 Macmillan Publishers Limited.

Auffarth B.,Foundation for Research and Technology Hellas | Auffarth B.,Free University of Berlin | Auffarth B.,Bernstein Center for Computational Neuroscience | Auffarth B.,KTH Royal Institute of Technology
Neuroscience and Biobehavioral Reviews | Year: 2013

The main problem with sensory processing is the difficulty in relating sensory input to physiological responses and perception. This is especially problematic at higher levels of processing, where complex cues elicit highly specific responses. In olfaction, this relationship is particularly obfuscated by the difficulty of characterizing stimulus statistics and perception. The core questions in olfaction are hence the so-called stimulus problem, which refers to the understanding of the stimulus, and the structure-activity and structure-odor relationships, which refer to the molecular basis of smell. It is widely accepted that the recognition of odorants by receptors is governed by the detection of physico-chemical properties and that the physical space is highly complex. Not surprisingly, ideas differ about how odor stimuli should be classified and about the very nature of information that the brain extracts from odors. Even though there are many measures for smell, there is none that accurately describes all aspects of it. Here, we summarize recent developments in the understanding of olfaction. We argue that an approach to olfactory function where information processing is emphasized could contribute to a high degree to our understanding of smell as a perceptual phenomenon emerging from neural computations. Further, we argue that combined analysis of the stimulus, biology, physiology, and behavior and perception can provide new insights into olfactory function. We hope that the reader can use this review as a competent guide and overview of research activities in olfactory physiology, psychophysics, computation, and psychology. We propose avenues for research, particularly in the systematic characterization of receptive fields and of perception. © 2013 Elsevier Ltd.

Stein T.,University of Trento | Sterzer P.,Charite Campus Mitte | Sterzer P.,Bernstein Center for Computational Neuroscience | Peelen M.V.,University of Trento
Cognition | Year: 2012

The rapid visual detection of other people in our environment is an important first step in social cognition. Here we provide evidence for selective sensitivity of the human visual system to upright depictions of conspecifics. In a series of seven experiments, we assessed the impact of stimulus inversion on the detection of person silhouettes, headless bodies, faces and other objects from a wide range of animate and inanimate control categories. We used continuous flash suppression (CFS), a variant of binocular rivalry, to render stimuli invisible at the beginning of each trial and measured the time upright and inverted stimuli needed to overcome such interocular suppression. Inversion strongly interfered with access to awareness for human faces, headless human bodies, person silhouettes, and even highly variable body postures, while suppression durations for control objects were not (inanimate objects) or only mildly (animal faces and bodies) affected by inversion. Furthermore, inversion effects were eliminated when the normal body configuration was distorted. The absence of strong inversion effects in a binocular control condition not involving interocular suppression suggests that non-conscious mechanisms mediated the effect of inversion on body and face detection during CFS. These results indicate that perceptual mechanisms that govern access to visual awareness are highly sensitive to the presence of conspecifics. © 2012 Elsevier B.V.

Kayser C.,Max Planck Institute for Biological Cybernetics | Kayser C.,Bernstein Center for Computational Neuroscience | Ng B.S.W.,Max Planck Institute for Biological Cybernetics | Ng B.S.W.,Bernstein Center for Computational Neuroscience | Schroeder T.,Max Planck Institute for Biological Cybernetics
Journal of Neuroscience | Year: 2012

Oscillatory activity in sensory cortices reflects changes in local excitation-inhibition balance, and recent work suggests that phase signatures of ongoing oscillations predict the perceptual detection of subsequent stimuli. Low-frequency oscillations are also entrained by dynamic natural scenes, suggesting that the chance of detecting a brief target depends on the relative timing of this to the entrained rhythm. We tested this hypothesis in humans by implementing a cocktail-party-like scenario requiring subjects to detect a target embedded in a cacophony of background sounds. Using EEG to measure auditory cortical oscillations, we find that the chance of target detection systematically depends on both power and phase of theta-band (2-6 Hz) but not alpha-band (8-12 Hz) oscillations before target. Detection rates were higher and responses faster when oscillatory power was low and both detection rate and response speed were modulated by phase. Intriguingly, the phase dependency was stronger for miss than for hit trials, suggesting that phase has a inhibiting but not ensuring role for detection. Entrainment of theta range oscillations prominently occurs during the processing of attended complex stimuli, such as vocalizations and speech. Our results demonstrate that this entrainment to attended sensory environments may have negative effects on the detection of individual tokens with in the environment, and they support the notion that specific phase ranges of cortical oscillations act as gatekeepers for perception. © 2012 the authors.

Spitzer B.,Bernstein Center for Computational Neuroscience | Wacker E.,Bernstein Center for Computational Neuroscience | Blankenburg F.,Bernstein Center for Computational Neuroscience
Journal of Neuroscience | Year: 2010

Previous animal research has revealed neuronal activity underlying short-term retention of vibrotactile stimuli, providing evidence for a parametric representation of stimulus frequency in primate tactile working memory (Romo et al., 1999). Here, we investigated the neural correlates of vibrotactile frequency processing in human working memory, using noninvasive electroencephalography (EEG). Participants judged the frequencies of vibrotactile stimuli delivered to the fingertip in a delayed match-to-sample frequency discrimination task. As expected, vibrotactile stimulation elicited pronounced steady-state evoked potentials, which were source-localized in primary somatosensory cortex. Furthermore, parametric analysis of induced EEG responses revealed that the frequency of stimulation was reflected by systematic modulations of synchronized oscillatory activity in nonprimary cortical areas. Stimulus processing was accompanied by frequency-dependent alpha-band responses (8-12 Hz) over dorsal occipital cortex. The critical new finding was that, throughout the retention interval, the stimulus frequency held in working memory was systematically represented by a modulation in prefrontal beta activity (20-25 Hz), which was source-localized to the inferior frontal gyrus. This modulation in oscillatory activity during stimulus retention was related to successful frequency discrimination, thus reflecting behaviorally relevant information. Together, the results complement previous findings of parametric working memory correlates in nonhuman primates and suggest that the quantitative representation of vibrotactile frequency in sensory memory entails systematic modulations of synchronized neural activity in human prefrontal cortex. Copyright © 2010 the authors.

Gollisch T.,Max Planck Institute of Neurobiology | Gollisch T.,Bernstein Center for Computational Neuroscience | Meister M.,Harvard University
Neuron | Year: 2010

We rely on our visual system to cope with the vast barrage of incoming light patterns and to extract features from the scene that are relevant to our well-being. The necessary reduction of visual information already begins in the eye. In this review, we summarize recent progress in understanding the computations performed in the vertebrate retina and how they are implemented by the neural circuitry. A new picture emerges from these findings that helps resolve a vexing paradox between the retina's structure and function. Whereas the conventional wisdom treats the eye as a simple prefilter for visual images, it now appears that the retina solves a diverse set of specific tasks and provides the results explicitly to downstream brain areas. © 2010 Elsevier Inc. All rights reserved.

Pamir E.,Bernstein Center for Computational Neuroscience
Learning & memory (Cold Spring Harbor, N.Y.) | Year: 2011

Conditioned behavior as observed during classical conditioning in a group of identically treated animals provides insights into the physiological process of learning and memory formation. However, several studies in vertebrates found a remarkable difference between the group-average behavioral performance and the behavioral characteristics of individual animals. Here, we analyzed a large number of data (1640 animals) on olfactory conditioning in the honeybee (Apis mellifera). The data acquired during absolute and differential classical conditioning differed with respect to the number of conditioning trials, the conditioned odors, the intertrial intervals, and the time of retention tests. We further investigated data in which animals were tested for spontaneous recovery from extinction. In all data sets we found that the gradually increasing group-average learning curve did not adequately represent the behavior of individual animals. Individual behavior was characterized by a rapid and stable acquisition of the conditioned response (CR), as well as by a rapid and stable cessation of the CR following unrewarded stimuli. In addition, we present and evaluate different model hypotheses on how honeybees form associations during classical conditioning by implementing a gradual learning process on the one hand and an all-or-none learning process on the other hand. In summary, our findings advise that individual behavior should be recognized as a meaningful predictor for the internal state of a honeybee--irrespective of the group-average behavioral performance.

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