Feedback of visual object information to foveal retinotopic cortex

Williams, Mark A.; Baker, Chris I.; Beeck, Hans Op de; Shim, Won Mok; Dang, Sabin; Triantafyllou, Christina; Kanwisher, Nancy

doi:10.1038/nn.2218

Cited by 193 publications

(260 citation statements)

References 36 publications

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“…More recent work indicates that nonstimulated regions of V1 contain information about stimuli presented elsewhere in the visual field and that they receive this information via corticocortical top-down (rather than lateral) projections. 69,70 Early visual cortices also encode information about stimuli presented in modalities other than the visual, 71,72 and analogous findings exist for the early auditory 71,73 and somatosensory 71,74 cortices. All of these findings indicate that top-down signals can induce, in their target areas, activity patterns of considerable resolution.…”

Section: Top-down Signals and Conscious Perception: What We Already Knowmentioning

confidence: 60%

The Role of Dendritic Signaling in the Anesthetic Suppression of Consciousness

Meyer

2015

Anesthesiology

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Despite considerable progress in the identification of the molecular targets of general anesthetics, it remains unclear how these drugs affect the brain at the systems level to suppress consciousness. According to recent proposals, anesthetics may achieve this feat by interfering with corticocortical topdown processes, that is, by interrupting information flow from association to early sensory cortices. Such a view entails two immediate questions. First, at which anatomical site, and by virtue of which physiological mechanism, do anesthetics interfere with top-down signals? Second, why does a breakdown of top-down signaling cause unconsciousness? While an answer to the first question can be gleaned from emerging neurophysiological evidence on dendritic signaling in cortical pyramidal neurons, a response to the second is offered by increasingly popular theoretical frameworks that place the element of prediction at the heart of conscious perception. Science magazine posed this question in a special section titled "What don't we know?," dedicated to the greatest challenges of contemporary science. 1 "Scientists are chipping away at the drugs' effects on individual neurons," the article reads, "but understanding how they render us unconscious will be a tougher nut to crack." This prediction proved correct: a decade later, we have expanded considerably our knowledge of the molecular targets of general anesthetics, but it remains enigmatic how these drugs affect the brain at the systems level. Why does the potentiation of γ-aminobutyric acid (GABA) receptors caused by propofol or desflurane cause unconsciousness? How are the brain's computational processes affected by this and other molecular mechanisms of anesthetics, so that patients undergoing surgery cease to experience their surrounds in terms of sight, sound, and touch? Anesthesiologists and cognitive neuroscientists alike have been captivated by these questions and have proposed a number of models in an attempt to answer them, such as Flohr's "information processing theory of anesthesia," 2 Alkire's "thalamic consciousness switch hypothesis," 3-6 Mashour's "cognitive unbinding paradigm," 7,8 John and Prichep's "anesthetic cascade," 9 or Hudetz's "forgotten present." 10,11 We shall return to some of these frameworks in a later section of the article.One recent development is particularly intriguing. Given that the most striking feature of general anesthesia is an interruption of the patient's ability to perceive the environment, it would appear intuitive for anesthetics to interfere primarily with bottom-up information flow along the sensory pathways, that is, with the signals that carry perceptual information from the thalamus to the primary sensory cortices and on to unimodal and multimodal association cortices. However, the very opposite appears to be the case. Several recent studies-carried out in both humans and animals, and using a variety of different anesthetic agents-have investigated differences in directional corticocortical connectivity bet...

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Section: Top-down Signals and Conscious Perception: What We Already Knowmentioning

confidence: 60%

The Role of Dendritic Signaling in the Anesthetic Suppression of Consciousness

Meyer

2015

Anesthesiology

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“…These differences may have arisen from variations in (i) measurement methodology (traveling wave vs. pRF modeling), (ii) signal-to-noise ratios, and (iii) effects arising from the stimulus types, such as perceptual filling in. Our moving bar stimulus, for example, likely produced a greater effect of filling in, which might be reflected in top-down influences producing activity in foveal V2, V3, hV4, and VO-1 (19,47). Along these lines, a recent study by Williams et al (19) showed that feedback from higher cortical areas can produce differential effects in the fovea vs. the periphery of early visual cortex.…”

Section: Comparisons With Studies On the Cortical Effects Of Other Rementioning

confidence: 83%

“…Third, it is expected that neurons with RFs partially eclipsed by the SPZ may show a scaling of their RF sizes, although whether these increase or decrease in size is difficult to predict. Such neurons' new RF spans will necessarily be reduced by the overlap with the SPZ, but their RF sizes may also be increased because of changes in feedback activity or a reduction in lateral inhibitory connections to nearby neurons that have also been silenced or shifted to ectopic locations by the scotoma (1,2,(17)(18)(19)(20). The combination of these effects could also lead to no observable change at this level of measurement.…”

Section: Significancementioning

confidence: 99%

fMRI of the rod scotoma elucidates cortical rod pathways and implications for lesion measurements

Barton

Brewer

2015

Proc. Natl. Acad. Sci. U.S.A.

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Are silencing, ectopic shifts, and receptive field (RF) scaling in cortical scotoma projection zones (SPZs) the result of long-term reorganization (plasticity) or short-term adaptation? Electrophysiological studies of SPZs after retinal lesions in animal models remain controversial, because they are unable to conclusively answer this question because of limitations of the methodology. Here, we used functional MRI (fMRI) visual field mapping through population RF (pRF) modeling with moving bar stimuli under photopic and scotopic conditions to measure the effects of the rod scotoma in human early visual cortex. As a naturally occurring central scotoma, it has a large cortical representation, is free of traumatic lesion complications, is completely reversible, and has not reorganized under normal conditions (but can as seen in rod monochromats). We found that the pRFs overlapping the SPZ in V1, V2, V3, hV4, and VO-1 generally (i) reduced their blood oxygen level-dependent signal coherence and (ii) shifted their pRFs more eccentric but (iii) scaled their pRF sizes in variable ways. Thus, silencing, ectopic shifts, and pRF scaling in SPZs are not unique identifiers of cortical reorganization; rather, they can be the expected result of short-term adaptation. However, are there differences between rod and cone signals in V1, V2, V3, hV4, and VO-1? We did not find differences for all five maps in more peripheral eccentricities outside of rod scotoma influence in coherence, eccentricity representation, or pRF size. Thus, rod and cone signals seem to be processed similarly in cortex. can adult human visual cortex reorganize after the removal of visual input?" This question can be studied through the effects of retinal lesions (causing scotomas), in which input from the retina has been removed, but cortical representations of the scotoma projection zone (SPZ) remain intact. Accordingly, emphasis must be placed on teasing apart effects of scotomas that relate to short-term cortical adaptation from those of long-term cortical plasticity (1) (terminology review is in ref.2). Here, we investigate this question in human cortex by using functional MRI (fMRI) to measure the immediate cortical SPZ responses in the unique paradigm of the naturally occurring rod scotoma.The photoreceptors in humans can be divided into two classes: cones, which are primarily responsible for vision under high-luminance (photopic) conditions, and rods, which are primarily responsible for vision under low-luminance (scotopic) conditions when the cones are inactive. The cones are an order of magnitude more highly concentrated in the fovea relative to the periphery, where they inform our most detailed visual experience (3). In contrast, the greatest concentrations of rods are more than ∼10°e ccentric from fixation and become increasingly sparse toward fixation until they are completely absent. This roughly circular rodfree zone covers a radius of ∼0.6-0.8°of visual angle about the fixation point (diameter = ∼1.25-1.7°) (4, 5). Under scotopic conditions, a...

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“…Instead, active predictions about upcoming sensory events continuously influence the incoming signal and interact as top-down projections with earliest perceptual processes (Bar, 2007;Carlsson, Petrovic, Skare, Petersson, & Ingvar, 2000;Churchland et al, 1994;Corbetta & Shulman, 2002;Engel, Fries, & Singer, 2001;Enns & Lleras, 2008;Gilbert & Sigman, 2007;Kastner, Pinsk, De Weerd, Desimone, & Ungerleider, 1999;Kutas, 2006;Kveraga, Ghuman, & Bar, 2007;McClelland & Rumelhart, 1981;Mechelli, Price, Friston, & Ishai, 2004;O'Connor, Fukui, Pinsk, & Kastner, 2002;Somers, Dale, Seiffert, & Tootell, 1999;Williams, Baker, Op de Beeck, Mok Shim, Dang, Triantafyllou et al, 2008).…”

Section: Predictability: Top-down Expectationsmentioning

confidence: 99%

Stimulus onset asynchrony and the timeline of word recognition: Event-related potentials during sentence reading

et al. 2012

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Article in press in Neuropsychologia [http://dx.doi.org/10.1016/j.neuropsychologia.2012.04.011] Please note that this unproofed preprint may be subject to minor changes. [May 5, 2012] SOA and the Timeline of Word Recognition 2 AbstractThree ERP experiments examined the effect of word presentation rate (i.e., stimulus onset asynchrony, SOA) on the time course of word frequency and predictability effects in sentence reading. In Experiments 1 and 2, sentences were presented word-by-word in the screen center at an SOA of 700 and 490 ms, respectively. While these rates are typical for psycholinguistic ERP research, natural reading happens at a considerably faster pace. Accordingly, Experiment 3 employed a near-normal SOA of 280 ms, which approximated the rate of normal reading. Main results can be summarized as follows: (1) The onset latency of early frequency effects decreases gradually with increasing presentation rates. (2) An early interaction between top-down and bottom-up processing is observed only under a nearnormal SOA. (3) N400 predictability effects occur later and are smaller at a near-normal (i.e., high) presentation rate than at the lower rates commonly used in ERP experiments. (4) ERP morphology is different at the shortest compared to longer SOAs. Together, the results point to a special role of a near-normal presentation rate for visual word recognition and therefore suggest that SOA should be taken into account in research of natural reading.

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Feedback of visual object information to foveal retinotopic cortex

Cited by 193 publications

References 36 publications

The Role of Dendritic Signaling in the Anesthetic Suppression of Consciousness

The Role of Dendritic Signaling in the Anesthetic Suppression of Consciousness

fMRI of the rod scotoma elucidates cortical rod pathways and implications for lesion measurements

Stimulus onset asynchrony and the timeline of word recognition: Event-related potentials during sentence reading

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