Séminaire - LPP, Daniel Baldauf: Cortical Mechanisms of Attention, Paris, 6 mars 2017

Publié le par ANAE

LPP seminar: Daniel Baldauf, CIMeC - Centre for Mind and Brain Sciences, University of Trento

 

6 March 2017, at 11h

 

Salle de réunion du LPP, H432, 4ème étage, Centre Biomédical des Saints Pères 45 rue des Sts Pères, 75006 Paris

 

Cortical Mechanisms of Attention

 

Over the last years, the neural mechanisms of spatial attention, via feedback signals from spatially-mapped control areas in frontal / parietal cortex, have been described in much detail. For non-spatial attention to different sensory modalities, complex objects, and so on, the control mechanisms seem much more complex and experimental work has just begun to identify possible sources of top-down control in the inferior part of frontal cortex.

 

Obviously, however, spatial and non-spatial attention are often combined in everyday tasks. How these different control networks work together is a major question in cognitive neuroscience.

 

To answer these remaining questions, we combined MEG and fMRI data in human subjects to identify not only the sources for spatial and non-spatial feedback signals, but also the mechanisms by which these different networks interact with sensory areas in attention.

 

We identified two separable networks in the superior- and inferior-frontal cortex, mediating spatial versus non-spatial attention, respectively. Using multi-voxel pattern analysis, we found spatial and non-spatial information are represented in different subpopulations of frontal cortex.

 

Most importantly, our analyses of temporally high-resolving MEG data also show that both control structures engage selectively in coherent interactions with sensory areas that represent the attended stimulus. Rather than a zero-phase lag connection, which would indicate common input, the interactions between frontal cortex and sensory areas are phase-shifted to allow for a 20ms transmission time. This seems to be just the right time for signals in one area to arrive at a time of maximum depolarization in the connected area, increasing their impact. Further, we were able to identify top-down directionality of these oscillatory interactions, establishing the superior- versus inferior-frontal cortex as key sources of spatial versus non-spatial attentional inputs, respectively. Finally, we combined transcranial current stimulation (tACS) with MEG recordings to directly test the causal role of local oscillation patterns in visual attention. After stimulating visual cortex we used evoked responses to evaluate the effects of frequency entrainment on the attentional weighting of visual input. By analyzing both phase and power spectra of the entrained rhythms we show how experimentally induced alpha rhythms lead to lasting inhibition and, in consequence, to suppressed visual responses, mimicking effects of visual attention.

 

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