http://precedings.nature.com/tags/visual%20cortex Recently posted documents tagged with 'visual cortex' Nature Publishing Group en Nature Precedings http://precedings.nature.com/images/header_logo.gif http://precedings.nature.com http://dx.doi.org/10.1038/npre.2009.3244.1 We reviewed the existing research linking visual mental imagery and phosphenes induced by TMS. We examined and contrasted conditions (and parameters) under which intensity and amplitude of TMS application at various cortical sites along the ventral and dorsal visual pathways: 1) induces the experience of visual images during perception and mental imagery, 2) interferes with or facilitates perception and/or imagery in concurrent and dual task conditions, 3) correlates with self-reports such as vividness ratings, and 4) reduces or has other selective effects on phosphene threshold in concomitance with perception and imagery. We propose an interpretation of the results of this mini-review within a new biophysical framework for visual mental imagery based on Bokkon’s redox molecular model of explicit optical coding of visual information in early visual areas (V1) and the propagation of conscious visual content at other levels in the stream of visual processing and in other parts of the brain. http://dx.doi.org/10.1038/npre.2009.3244.1 Thu, 14 May 2009 07:49:27 UTC TMS, phosphenes and visual mental imagery: A mini-review and a theoretical framework doi:10.1038/npre.2009.3244.1 2009-05-14 Amedeo D'Angiulli Nature Precedings 2009-05-14T07:49:27Z Poster Neuroscience http://creativecommons.org/licenses/by/3.0/ http://precedings.nature.com/documents/2246/version/1 When an image is presented to one eye and a very different image is presented to the corresponding location of the other eye, they compete for conscious representation, such that only one image is visible at a time while the other is suppressed. Called binocular rivalry, this phenomenon and its deviants have been extensively exploited to study the mechanism and neural correlates of consciousness. In this paper, we propose a framework, the unconscious binding hypothesis, to distinguish unconscious processing from conscious processing. According to this framework, the unconscious mind not only encodes individual features but also temporally binds distributed features to give rise to cortical representation, but unlike conscious binding, such unconscious binding is fragile. Under this framework, we review evidence from psychophysical and neuroimaging studies, which suggests that: (1) for invisible low level features, prolonged exposure to visual pattern and simple translational motion can alter the appearance of subsequent visible features (i.e. adaptation); for invisible high level features, although complex spiral motion cannot produce adaptation, nor can objects/words enhance subsequent processing of related stimuli (i.e. priming), images of tools can nevertheless activate the dorsal pathway; and (2) although invisible central cues cannot orient attention, invisible erotic pictures in the periphery can nevertheless guide attention, likely through emotional arousal; reciprocally, the processing of invisible information can be modulated by attention at perceptual and neural levels. http://precedings.nature.com/documents/2246/version/1 Tue, 02 Sep 2008 18:55:51 UTC Seeing the invisible: The scope and limits of unconscious processing in binocular rivalry hdl:10101/npre.2008.2246.1 2008-09-02 Zhicheng Lin Nature Precedings 2008-09-02T18:55:51Z Manuscript Neuroscience http://creativecommons.org/licenses/by/3.0/ http://precedings.nature.com/documents/1827/version/1 The neural mechanisms responsible for triggering visual hallucinations are poorly understood. Here, we report a unique patient whose hallucinations consist exclusively of faces, and which could be reliably precipitated by looking at trees. Using functional Magnetic Resonance Imaging (fMRI), we found that, while face hallucinations was associated with increased neural activity in a number of cortical regions, including low-level visual areas, there was significant decreased activity in the right fusiform face area, a region that is empirically defined by increase activity during veridical perception of faces. These findings indicate key differences in how hallucinatory and veridical perceptions lead to the same phenomenological experience of seeing faces, and are consistent with the hypothesis that hallucinations may be generated by decreased inhibitory inputs to key cortical regions, in contrast to the excitatory synaptic inputs underlying veridical perception. http://precedings.nature.com/documents/1827/version/1 Tue, 22 Apr 2008 21:21:06 UTC Seeing faces: evidence suggesting cortical disinhibition in the genesis of visual hallucinations. hdl:10101/npre.2008.1827.1 2008-05-23 Giuseppe Iaria Nature Precedings 2008-04-22T21:21:06Z Manuscript Neuroscience http://creativecommons.org/licenses/by/3.0/ http://precedings.nature.com/documents/1563/version/1 A dorsal fronto-parietal network, including regions in intra-parietal sulcus (IPS) and frontal eye field (FEF), has been hypothesized to control the allocation of spatial attention to environmental stimuli. One putative mechanism of control is the de-synchronization of electroencephalography (EEG) alpha rhythms (~8-12 Hz) in parieto-occipital cortex in anticipation of a visual target. We show that brief interference by transcranial magnetic stimulation (rTMS) with preparatory activity in right IPS or right FEF while subjects attend to a spatial location impairs identification of target stimuli ~2 seconds later. Moreover, the visual deficit relates to the disruption of anticipatory (pre-stimulus) alpha desynchronization and its topography in parieto-occipital cortex. After right IPS stimulation, the degree to which alpha desynchronization is suppressed predicts the speed of visual identification. These results demonstrate the causal role of posterior parietal cortex in the control of visuo-spatial attention exerted through the synchronization of visual neurons. http://precedings.nature.com/documents/1563/version/1 Fri, 01 Feb 2008 18:25:26 UTC Posterior parietal cortex controls spatial attention through modulation of anticipatory alpha rhythms hdl:10101/npre.2008.1563.1 2008-02-01 Paolo Capotosto Nature Precedings 2008-02-01T18:25:26Z Manuscript Neuroscience http://creativecommons.org/licenses/by/3.0/