dinsdag 26 april 2011

Inter-area correlations in the ventral visual pathway reflect feature integr...

 
 

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via Journal of Vision recent issues door Freeman, J., Donner, T. H., Heeger, D. J. op 26-4-11

During object perception, the brain integrates simple features into representations of complex objects. A perceptual phenomenon known as visual crowding selectively interferes with this process. Here, we use crowding to characterize a neural correlate of feature integration. Cortical activity was measured with functional magnetic resonance imaging, simultaneously in multiple areas of the ventral visual pathway (V1–V4 and the visual word form area, VWFA, which responds preferentially to familiar letters), while human subjects viewed crowded and uncrowded letters. Temporal correlations between cortical areas were lower for crowded letters than for uncrowded letters, especially between V1 and VWFA. These differences in correlation were retinotopically specific, and persisted when attention was diverted from the letters. But correlation differences were not evident when we substituted the letters with grating patches that were not crowded under our stimulus conditions. We conclude that inter-area correlations reflect feature integration and are disrupted by crowding. We propose that crowding may perturb the transformations between neural representations along the ventral pathway that underlie the integration of features into objects.


 
 

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dinsdag 7 december 2010

The surface area of human V1 predicts the subjective experience of object size.

The bigger your V1, the less illusions you see...

 
 

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per pubmed: top authors autorius Schwarzkopf DS, Song C, Rees G 10.12.7

Related Articles

The surface area of human V1 predicts the subjective experience of object size.

Nat Neurosci. 2010 Dec 5;

Authors: Schwarzkopf DS, Song C, Rees G

The surface area of human primary visual cortex (V1) varies substantially between individuals for unknown reasons. We found that this variability was strongly and negatively correlated with the magnitude of two common visual illusions, where two physically identical objects appear different in size as a result of their context. Because such illusions dissociate conscious perception from physical stimulation, our findings indicate that the surface area of V1 predicts variability in conscious experience.

PMID: 21131954 [PubMed - as supplied by publisher]


 
 

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maandag 25 oktober 2010

Cognitive neuroscience 2.0: building a cumulative science of human brain function

 

http://www.cell.com/trends/cognitive-sciences/abstract/S1364-6613(10)00201-9

 

maandag 11 oktober 2010

Interpreting brain images: reflections on an adolescent field

Book review; the book might be interesting.

 

 

Feed: TRENDS IN COGNITIVE SCIENCES
Posted on: dinsdag 28 september 2010 6:00
Author: TRENDS IN COGNITIVE SCIENCES
Subject: Interpreting brain images: reflections on an adolescent field

 

Nikolaus Kriegeskorte.


View article...

Suggested by Maarten

dinsdag 5 oktober 2010

Optogenetic interrogation of neural circuits: technology for probing mammalian brain structures

http://www.nature.com/nprot/journal/v5/n3/full/nprot.2009.226.html

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Naoki Kogo, PhD
Laboratory of Experimental Psychology
Department of Psychology, University of Leuven, Belgium
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Optogenetic fMRI Sheds Light on the Neural Basis of the BOLD Signal

 
 

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via Journal of Neurophysiology current issue by Palmer, H. S. on 10/4/10

Blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) is widely used as a measure of neuronal activity, despite an incomplete understanding of the hemodynamic and neural bases for BOLD signals. Recent work by Lee and colleagues investigated whether activating genetically specified neurons elicits BOLD responses. Integrating optogenetic control of specific cells and fMRI showed that stimulating excitatory neurons triggers a positive BOLD signal with conventional kinetics locally and delayed weaker BOLD signals distally.


 
 

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Global and local fMRI signals driven by neurons defined optogenetically by t...

 
 

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via Nature - Issue - nature.com science feeds by Karl Deisseroth on 5/16/10

Global and local fMRI signals driven by neurons defined optogenetically by type and wiring

Nature 465, 788 (2010). doi:10.1038/nature09108

Authors: Jin Hyung Lee, Remy Durand, Viviana Gradinaru, Feng Zhang, Inbal Goshen, Dae-Shik Kim, Lief E. Fenno, Charu Ramakrishnan & Karl Deisseroth

Despite a rapidly-growing scientific and clinical brain imaging literature based on functional magnetic resonance imaging (fMRI) using blood oxygenation level-dependent (BOLD) signals, it remains controversial whether BOLD signals in a particular region can be caused by activation of local excitatory neurons. This difficult question is central to the interpretation and utility of BOLD, with major significance for fMRI studies in basic research and clinical applications. Using a novel integrated technology unifying optogenetic control of inputs with high-field fMRI signal readouts, we show here that specific stimulation of local CaMKIIα-expressing excitatory neurons, either in the neocortex or thalamus, elicits positive BOLD signals at the stimulus location with classical kinetics. We also show that optogenetic fMRI (ofMRI) allows visualization of the causal effects of specific cell types defined not only by genetic identity and cell body location, but also by axonal projection target. Finally, we show that ofMRI within the living and intact mammalian brain reveals BOLD signals in downstream targets distant from the stimulus, indicating that this approach can be used to map the global effects of controlling a local cell population. In this respect, unlike both conventional fMRI studies based on correlations and fMRI with electrical stimulation that will also directly drive afferent and nearby axons, this ofMRI approach provides causal information about the global circuits recruited by defined local neuronal activity patterns. Together these findings provide an empirical foundation for the widely-used fMRI BOLD signal, and the features of ofMRI define a potent tool that may be suitable for functional circuit analysis as well as global phenotyping of dysfunctional circuitry.


 
 

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