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Cortical synchronization suggests neural principles of visual feature grouping

100%
Eckhorn R.
Acta Neurobiologiae Experimentalis
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2000
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vol. 60
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issue 2
261-269
EN
Compositions of visual scenes are related here to neural signals in visual cortex and to cortical circuit models to understand neural mechanisms of perceptual feature grouping. Starting from the hypothesis that synchronization and decoupling of cortical gamma-activities (35-90 Hz) define the relations among visual objects, we concentrate on synchronization related to (1) static retinal stimulation during ocular fixation, and (2) transient stimulation by sudden shifts in object position. The synchronization hypothesis has been tested by analyzing signal correlations in visual cortex of monkeys with the following results: Static retinal stimuli induce loosely phase-coupled gamma-activities among neurons of an object's cortical representation. Patches of gamma-synchronization become decoupled across the representation of an object's contour, and therby can code figure-ground segregation. Transient stimuli evoke synchronized volleys of stimulus-locked activities that are typically non-rhythmic and include low frequency components in addition to those in the gamma-range. It is argued that stimulus-induced and stimulus-locked synchronizations may play different roles in perceptual feature grouping.
2
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Surface-view connectivity patterns of area 18 in cats

88%
Pospichal M. W., Wimborne B. M., Stepniewska I., Kaas J. H.
Acta Neurobiologiae Experimentalis
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1996
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vol. 56
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issue 3
657-671
EN
To determine surface-view connectivity patterns of area 18, separate injections of up to six anatomical tracers were delivered to various rostrocaudal locations of area 18 in six normal cats.Subsequently, cortex was separated from subcortical structures, mannually flattened, and cut parallel to the surface.Result reveal that ipsilateral cortical connections of area 18 with three region of cortex are topological. In areas 17 and 19, separate patches of cells labeled with different tracers progressed in a rostrocaudal sequence corresponding to the order of the injections.A similar but less precise pattern of rostrocaudal labelling occured in more lateral visual cortex, even though several presumptive visual areas were involved.Thus anteromedial suprasylvian cortex projected to anterior area 18 while more posterolateral suprasylvian cortex projected to postrior area 18.There was no evidence of double-labelled cells projecting to separate regions in area 18.These results are more consistent with the concept of a single suprasylvian area projecting to area 18 cortex than several.
3
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20 Hz rhythm of activity in visual system of perceiving cat

88%
Bekisz M., Wrobel A.
Acta Neurobiologiae Experimentalis
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1993
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vol. 53
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issue 1
175-182
EN
Cats attended to either visual or acoustic moving stimuli in order to pereceive the location of their disappearance, with signaled reward in left or right foodwell. The analysis of concomitant electroencephalograms revealed an elevation of the 20 Hz band in the Fourier spectra of activity of respective visual and auditory projection cortices. These oscillations appeared only on the trials that ended with a successful response. With use of directed transfer functions we were able to show that during the visual task, the 20 Hz frequency was propagated from the spot of appearance along the visual cortex, as well as towards the lateral geniculate nucleus.
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