ORCID Profile
0000-0003-1765-3502
Current Organisation
University of Reading
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Publisher: Elsevier BV
Date: 05-2011
Publisher: Springer Science and Business Media LLC
Date: 23-09-2008
Publisher: Springer Netherlands
Date: 2012
Publisher: Frontiers Media SA
Date: 2012
Publisher: Frontiers Media SA
Date: 26-02-2015
Publisher: American Physical Society (APS)
Date: 1996
Publisher: Elsevier BV
Date: 03-2000
Publisher: WORLD SCIENTIFIC
Date: 10-2001
Publisher: Elsevier BV
Date: 04-1997
Publisher: Elsevier BV
Date: 12-1997
Publisher: Elsevier BV
Date: 06-2004
Publisher: Springer New York
Date: 2011
Publisher: American Physical Society (APS)
Date: 11-2007
Publisher: Elsevier BV
Date: 02-2013
DOI: 10.1016/J.NEUROIMAGE.2012.10.024
Abstract: Spontaneous activity of the brain at rest frequently has been considered a mere backdrop to the salient activity evoked by external stimuli or tasks. However, the resting state of the brain consumes most of its energy budget, which suggests a far more important role. An intriguing hint comes from experimental observations of spontaneous activity patterns, which closely resemble those evoked by visual stimulation with oriented gratings, except that cortex appeared to cycle between different orientation maps. Moreover, patterns similar to those evoked by the behaviorally most relevant horizontal and vertical orientations occurred more often than those corresponding to oblique angles. We hypothesize that this kind of spontaneous activity develops at least to some degree autonomously, providing a dynamical reservoir of cortical states, which are then associated with visual stimuli through learning. To test this hypothesis, we use a biologically inspired neural mass model to simulate a patch of cat visual cortex. Spontaneous transitions between orientation states were induced by modest modifications of the neural connectivity, establishing a stable heteroclinic channel. Significantly, the experimentally observed greater frequency of states representing the behaviorally important horizontal and vertical orientations emerged spontaneously from these simulations. We then applied bar-shaped inputs to the model cortex and used Hebbian learning rules to modify the corresponding synaptic strengths. After unsupervised learning, different bar inputs reliably and exclusively evoked their associated orientation state whereas in the absence of input, the model cortex resumed its spontaneous cycling. We conclude that the experimentally observed similarities between spontaneous and evoked activity in visual cortex can be explained as the outcome of a learning process that associates external stimuli with a preexisting reservoir of autonomous neural activity states. Our findings hence demonstrate how cortical connectivity can link the maintenance of spontaneous activity in the brain mechanistically to its core cognitive functions.
Publisher: WORLD SCIENTIFIC
Date: 10-2002
Publisher: Frontiers Media SA
Date: 05-03-2015
Publisher: Frontiers Media SA
Date: 2013
Publisher: Frontiers Media SA
Date: 2014
Publisher: Springer Science and Business Media LLC
Date: 13-07-2009
Publisher: Springer New York
Date: 2013
Publisher: Springer New York
Date: 2013
Publisher: American Physical Society (APS)
Date: 18-02-2020
Publisher: Springer Science and Business Media LLC
Date: 26-02-2014
Publisher: Public Library of Science (PLoS)
Date: 29-01-2010
Publisher: Springer Science and Business Media LLC
Date: 04-04-2010
DOI: 10.1007/S10548-010-0140-3
Abstract: Progress in functional neuroimaging of the brain increasingly relies on the integration of data from complementary imaging modalities in order to improve spatiotemporal resolution and interpretability. However, the usefulness of merely statistical combinations is limited, since neural signal sources differ between modalities and are related non-trivially. We demonstrate here that a mean field model of brain activity can simultaneously predict EEG and fMRI BOLD with proper signal generation and expression. Simulations are shown using a realistic head model based on structural MRI, which includes both dense short-range background connectivity and long-range specific connectivity between brain regions. The distribution of modeled neural masses is comparable to the spatial resolution of fMRI BOLD, and the temporal resolution of the modeled dynamics, importantly including activity conduction, matches the fastest known EEG phenomena. The creation of a cortical mean field model with anatomically sound geometry, extensive connectivity, and proper signal expression is an important first step towards the model-based integration of multimodal neuroimages.
Publisher: Society for Neuroscience
Date: 09-03-2011
DOI: 10.1523/JNEUROSCI.4697-10.2011
Abstract: Using simultaneous electroencephalography as a measure of ongoing activity and functional magnetic resonance imaging (fMRI) as a measure of the stimulus-driven neural response, we examined whether the litude and phase of occipital alpha oscillations at the onset of a brief visual stimulus affects the litude of the visually evoked fMRI response. When accounting for intrinsic coupling of alpha litude and occipital fMRI signal by modeling and subtracting pseudo-trials, no significant effect of prestimulus alpha litude on the evoked fMRI response could be demonstrated. Regarding the effect of alpha phase, we found that stimuli arriving at the peak of the alpha cycle yielded a lower blood oxygenation level-dependent (BOLD) fMRI response in early visual cortex (V1/V2) than stimuli presented at the trough of the cycle. Our results therefore show that phase of occipital alpha oscillations impacts the overall strength of a visually evoked response, as indexed by the BOLD signal. This observation complements existing evidence that alpha oscillations reflect periodic variations in cortical excitability and suggests that the phase of oscillations in postsynaptic potentials can serve as a mechanism of gain control for incoming neural activity. Finally, our findings provide a putative neural basis for observations of alpha phase dependence of visual perceptual performance.
Publisher: Elsevier BV
Date: 02-1999
Publisher: IEEE
Date: 08-2011
Publisher: American Physical Society (APS)
Date: 13-02-2003
Publisher: The Royal Society
Date: 13-10-2011
Abstract: Brain activity can be measured with several non-invasive neuroimaging modalities, but each modality has inherent limitations with respect to resolution, contrast and interpretability. It is hoped that multimodal integration will address these limitations by using the complementary features of already available data. However, purely statistical integration can prove problematic owing to the disparate signal sources. As an alternative, we propose here an advanced neural population model implemented on an anatomically sound cortical mesh with freely adjustable connectivity, which features proper signal expression through a realistic head model for the electroencephalogram (EEG), as well as a haemodynamic model for functional magnetic resonance imaging based on blood oxygen level dependent contrast (fMRI BOLD). It hence allows simultaneous and realistic predictions of EEG and fMRI BOLD from the same underlying model of neural activity. As proof of principle, we investigate here the influence on simulated brain activity of strengthening visual connectivity. In the future we plan to fit multimodal data with this neural population model. This promises novel, model-based insights into the brain's activity in sleep, rest and task conditions.
Publisher: Springer Science and Business Media LLC
Date: 13-07-2009
Publisher: Elsevier BV
Date: 06-2007
Publisher: AIP
Date: 2003
DOI: 10.1063/1.1607155
Publisher: Elsevier BV
Date: 10-1999
Publisher: Springer Science and Business Media LLC
Date: 2012
Publisher: Elsevier BV
Date: 10-2009
DOI: 10.1016/J.NEUNET.2009.07.014
Abstract: The bewildering complexity of cortical microcircuits at the single cell level gives rise to surprisingly robust emergent activity patterns at the level of laminar and columnar local field potentials (LFPs) in response to targeted local stimuli. Here we report the results of our multivariate data-analytic approach based on simultaneous multi-site recordings using micro-electrode-array chips for investigation of the microcircuitry of rat somatosensory (barrel) cortex. We find high repeatability of stimulus-induced responses, and typical spatial distributions of LFP responses to stimuli in supragranular, granular, and infragranular layers, where the last form a particularly distinct class. Population spikes appear to travel with about 33 cm/s from granular to infragranular layers. Responses within barrel related columns have different profiles than those in neighbouring columns to the left or interchangeably to the right. Variations between slices occur, but can be minimized by strictly obeying controlled experimental protocols. Cluster analysis on normalized recordings indicates specific spatial distributions of time series reflecting the location of sources and sinks independent of the stimulus layer. Although the precise correspondences between single cell activity and LFPs are still far from clear, a sophisticated neuroinformatics approach in combination with multi-site LFP recordings in the standardized slice preparation is suitable for comparing normal conditions to genetically or pharmacologically altered situations based on real cortical microcircuitry.
Publisher: WORLD SCIENTIFIC
Date: 09-2002
Publisher: Springer Science and Business Media LLC
Date: 05-02-2018
Publisher: Springer New York
Date: 2013
Publisher: American Physical Society (APS)
Date: 04-04-2005
Publisher: Springer Science and Business Media LLC
Date: 13-07-2009
Publisher: Springer International Publishing
Date: 2020
Publisher: Elsevier BV
Date: 08-1998
Publisher: Springer Science and Business Media LLC
Date: 13-07-2009
Location: United Kingdom of Great Britain and Northern Ireland
Location: No location found
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: Netherlands
Location: Australia
No related grants have been discovered for Ingo Bojak.