- Visual BOLD Response in Late Blind Subjects with Argus II Retinal Prosthesis. [Journal Article]
- PBPLoS Biol 2016; 14(10):e1002569
- Retinal prosthesis technologies require that the visual system downstream of the retinal circuitry be capable of transmitting and elaborating visual signals. We studied the capability of plastic remo...
Retinal prosthesis technologies require that the visual system downstream of the retinal circuitry be capable of transmitting and elaborating visual signals. We studied the capability of plastic remodeling in late blind subjects implanted with the Argus II Retinal Prosthesis with psychophysics and functional MRI (fMRI). After surgery, six out of seven retinitis pigmentosa (RP) blind subjects were able to detect high-contrast stimuli using the prosthetic implant. However, direction discrimination to contrast modulated stimuli remained at chance level in all of them. No subject showed any improvement of contrast sensitivity in either eye when not using the Argus II. Before the implant, the Blood Oxygenation Level Dependent (BOLD) activity in V1 and the lateral geniculate nucleus (LGN) was very weak or absent. Surprisingly, after prolonged use of Argus II, BOLD responses to visual input were enhanced. This is, to our knowledge, the first study tracking the neural changes of visual areas in patients after retinal implant, revealing a capacity to respond to restored visual input even after years of deprivation.
- Morphology of visual sector thalamic reticular neurons in the macaque monkey suggests retinotopically-specialized, parallel stream-mixed input to the lateral geniculate nucleus. [Journal Article]
- JCJ Comp Neurol 2016 Oct 25
- The thalamic reticular nucleus (TRN) is a unique brain structure at the interface between the thalamus and the cortex. Because the TRN receives bottom-up sensory input and top-down cortical input, it...
The thalamic reticular nucleus (TRN) is a unique brain structure at the interface between the thalamus and the cortex. Because the TRN receives bottom-up sensory input and top-down cortical input, it could serve as an integration hub for sensory and cognitive signals. Functional evidence supports broad roles for the TRN in arousal, attention, and sensory selection. How specific circuits connecting the TRN with sensory thalamic structures implement these functions is not known. The structural organization and function of the TRN is particularly interesting in the context of highly organized sensory systems, such as the primate visual system, where neurons in the retina and dorsal lateral geniculate nucleus of the thalamus (dLGN) are morphologically and physiologically distinct and also specialized for processing particular features of the visual environment. To gain insight into the functional relationship between the visual sector of the TRN and the dLGN, we reconstructed a large number of TRN neurons that were retrogradely labeled following injections of rabies virus expressing EGFP into the dLGN. An independent cluster analysis, based on 10 morphological metrics measured for each reconstructed neuron, revealed three clusters of TRN neurons that differed in cell body shape and size, dendritic arborization patterns, and medial-lateral position within the TRN. TRN dendritic and axonal morphologies are inconsistent with visual stream-specific projections to the dLGN. Instead, TRN neuronal organization could facilitate transmission of global arousal and/or cognitive signals to the dLGN with retinotopic precision that preserves specialized processing of foveal versus peripheral visual information. This article is protected by copyright. All rights reserved.
- A neural mechanism of dynamic gating of task-relevant information by top-down influence in primary visual cortex. [Journal Article]
- BBiosystems 2016 Sep 28; 150:138-148
- Visual recognition involves bidirectional information flow, which consists of bottom-up information coding from retina and top-down information coding from higher visual areas. Recent studies have de...
Visual recognition involves bidirectional information flow, which consists of bottom-up information coding from retina and top-down information coding from higher visual areas. Recent studies have demonstrated the involvement of early visual areas such as primary visual area (V1) in recognition and memory formation. V1 neurons are not passive transformers of sensory inputs but work as adaptive processor, changing their function according to behavioral context. Top-down signals affect tuning property of V1 neurons and contribute to the gating of sensory information relevant to behavior. However, little is known about the neuronal mechanism underlying the gating of task-relevant information in V1. To address this issue, we focus on task-dependent tuning modulations of V1 neurons in two tasks of perceptual learning. We develop a model of the V1, which receives feedforward input from lateral geniculate nucleus and top-down input from a higher visual area. We show here that the change in a balance between excitation and inhibition in V1 connectivity is necessary for gating task-relevant information in V1. The balance change well accounts for the modulations of tuning characteristic and temporal properties of V1 neuronal responses. We also show that the balance change of V1 connectivity is shaped by top-down signals with temporal correlations reflecting the perceptual strategies of the two tasks. We propose a learning mechanism by which synaptic balance is modulated. To conclude, top-down signal changes the synaptic balance between excitation and inhibition in V1 connectivity, enabling early visual area such as V1 to gate context-dependent information under multiple task performances.
- In Vivo Evaluation of the Visual Pathway in Streptozotocin-Induced Diabetes by Diffusion Tensor MRI and Contrast Enhanced MRI. [Journal Article]
- PlosPLoS One 2016; 11(10):e0165169
- Visual function has been shown to deteriorate prior to the onset of retinopathy in some diabetic patients and experimental animal models. This suggests the involvement of the brain's visual system in...
Visual function has been shown to deteriorate prior to the onset of retinopathy in some diabetic patients and experimental animal models. This suggests the involvement of the brain's visual system in the early stages of diabetes. In this study, we tested this hypothesis by examining the integrity of the visual pathway in a diabetic rat model using in vivo multi-modal magnetic resonance imaging (MRI). Ten-week-old Sprague-Dawley rats were divided into an experimental diabetic group by intraperitoneal injection of 65 mg/kg streptozotocin in 0.01 M citric acid, and a sham control group by intraperitoneal injection of citric acid only. One month later, diffusion tensor MRI (DTI) was performed to examine the white matter integrity in the brain, followed by chromium-enhanced MRI of retinal integrity and manganese-enhanced MRI of anterograde manganese transport along the visual pathway. Prior to MRI experiments, the streptozotocin-induced diabetic rats showed significantly smaller weight gain and higher blood glucose level than the control rats. DTI revealed significantly lower fractional anisotropy and higher radial diffusivity in the prechiasmatic optic nerve of the diabetic rats compared to the control rats. No apparent difference was observed in the axial diffusivity of the optic nerve, the chromium enhancement in the retina, or the manganese enhancement in the lateral geniculate nucleus and superior colliculus between groups. Our results suggest that streptozotocin-induced diabetes leads to early injury in the optic nerve when no substantial change in retinal integrity or anterograde transport along the visual pathways was observed in MRI using contrast agent enhancement. DTI may be a useful tool for detecting and monitoring early pathophysiological changes in the visual system of experimental diabetes non-invasively.
- Does the treatment of amblyopia normalise subfoveal choroidal thickness in amblyopic children? [Journal Article]
- CEClin Exp Optom 2016 Oct 18
- CONCLUSIONS: Although a six-month treatment of amblyopia increased the visual acuity of the anisometropic hyperopic amblyopic eyes, it could not significantly change choroidal thickness. Our results were in accordance with the conventional explanation, which suggests visual cortex and lateral geniculate nucleus abnormalities in the pathophysiology of amblyopia.
- Exploring Visual Attention Functions of the Human Extrageniculate Pathways Through Behavioral Cues. [Journal Article]
- PRPsychol Rev 2016 Oct 10
- Over the past few decades, evidence has accumulated showing that, at subcortical levels, visual attention depends partly on the extrageniculate neural pathways, that is, those pathways that bypass th...
Over the past few decades, evidence has accumulated showing that, at subcortical levels, visual attention depends partly on the extrageniculate neural pathways, that is, those pathways that bypass the lateral geniculate nucleus and circumvent the primary visual cortex. Working in concert with neuroscience, experimental psychology has contributed considerably to the understanding of the role these pathways play through the use of 3 behavioral cues: nasal-temporal asymmetries, responses to S-cone stimuli, and responses to perceptually suppressed stimuli. In this article, after presenting the extrageniculate pathways and the role of each of the component structures in visual attention, we review findings from studies that have used these behavioral cues, as well as what they tell us about the role of the extrageniculate pathways in visual attention. We conclude that nasal-temporal asymmetries and responses to S-cone stimuli are plausible probes of extrageniculate functions, because they are consistent with neurophysiological, neuropsychological, and neuroimaging findings. By contrast, despite promising perspectives, the literature is yet too scarce for responses to perceptually suppressed stimuli to be considered as a plausible probe of extrageniculate-dependent attention functions. (PsycINFO Database Record
- Skellam process with resetting: a neural spike train model. [Journal Article]
- SMStat Med 2016 Sep 26
- This paper introduces the Skellam process with resetting. Resetting is a modification that accommodates the modeling of neural spike trains. We show this as a biologically plausible model, which code...
This paper introduces the Skellam process with resetting. Resetting is a modification that accommodates the modeling of neural spike trains. We show this as a biologically plausible model, which codes the information content of neural spike trains with three, potentially, time-varying functions. We show that the interspike interval distribution under this model follows a mixture of gamma distributions, a flexible class covering a wide range of commonly used models. Through simulation studies and the analyses of connected retinal ganglion and lateral geniculate nucleus cells, we evaluate the performance of this model. Copyright © 2016 John Wiley & Sons, Ltd.
- Achromatic temporal-frequency responses of human lateral geniculate nucleus and primary visual cortex. [Journal Article]
- VRVision Res 2016; 127:177-85
- The sensitivity of the sensory systems to temporal changes of the environment constitutes one of the critical issues in perception. In the present study, we investigated the human early visual system...
The sensitivity of the sensory systems to temporal changes of the environment constitutes one of the critical issues in perception. In the present study, we investigated the human early visual system's dependency on the temporal frequency of visual input using fMRI. Blood oxygen level-dependent (BOLD) responses of the lateral geniculate nucleus (LGN) and primary visual cortex (V1) were investigated in a wide frequency range (6-46Hz) with fine frequency sampling (13 frequencies). Subject-specific functional-anatomic ROIs were derived from the combination of the anatomic template masks and the functional maps derived from multi-session fMRI analyses across all 13 stimulation conditions. Using functional-anatomic ROIs, average responses of LGN and V1 were calculated for each frequency. The V1 surface area was further parsed into 7 eccentricity sectors to detail central and peripheral responses. LGN's response revealed fluctuations on a background of non-significant decrease of the BOLD response with increasing stimulation frequency, while V1 response displayed similar fluctuations with a global maximum in the range of 8-12Hz, but a rapid and significant decrease with increasing stimulation frequency especially above 14Hz. This behavior of V1 response valid for both central and peripheral vision emphasizes that the profound low-pass effect of the visual system to visual input emerges in V1, presumably generated by the intra-cortical circuitry of V1 or projections from extra-striate areas. Besides, the high correlation between LGN and V1 BOLD responses across all visual stimulation frequencies supports the oscillatory tuning in thalamo-cortical interactions as previously claimed in electrophysiological studies.
- Representation of Perceptual Color Space in Macaque Posterior Inferior Temporal Cortex (the V4 Complex). [Journal Article]
- EeNeuro 2016 Jul-Aug; 3(4)
- The lateral geniculate nucleus is thought to represent color using two populations of cone-opponent neurons [L vs M; S vs (L + M)], which establish the cardinal directions in color space (reddish vs ...
The lateral geniculate nucleus is thought to represent color using two populations of cone-opponent neurons [L vs M; S vs (L + M)], which establish the cardinal directions in color space (reddish vs cyan; lavender vs lime). How is this representation transformed to bring about color perception? Prior work implicates populations of glob cells in posterior inferior temporal cortex (PIT; the V4 complex), but the correspondence between the neural representation of color in PIT/V4 complex and the organization of perceptual color space is unclear. We compared color-tuning data for populations of glob cells and interglob cells to predictions obtained using models that varied in the color-tuning narrowness of the cells, and the color preference distribution across the populations. Glob cells were best accounted for by simulated neurons that have nonlinear (narrow) tuning and, as a population, represent a color space designed to be perceptually uniform (CIELUV). Multidimensional scaling and representational similarity analyses showed that the color space representations in both glob and interglob populations were correlated with the organization of CIELUV space, but glob cells showed a stronger correlation. Hue could be classified invariant to luminance with high accuracy given glob responses and above-chance accuracy given interglob responses. Luminance could be read out invariant to changes in hue in both populations, but interglob cells tended to prefer stimuli having luminance contrast, regardless of hue, whereas glob cells typically retained hue tuning as luminance contrast was modulated. The combined luminance/hue sensitivity of glob cells is predicted for neurons that can distinguish two colors of the same hue at different luminance levels (orange/brown).
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- Measuring Connectivity in the Primary Visual Pathway in Human Albinism Using Diffusion Tensor Imaging and Tractography. [Journal Article]
- JVJ Vis Exp 2016 Aug 11; (114)
- In albinism, the number of ipsilaterally projecting retinal ganglion cells (RGCs) is significantly reduced. The retina and optic chiasm have been proposed as candidate sites for misrouting. Since a c...
In albinism, the number of ipsilaterally projecting retinal ganglion cells (RGCs) is significantly reduced. The retina and optic chiasm have been proposed as candidate sites for misrouting. Since a correlation between the number of lateral geniculate nucleus (LGN) relay neurons and LGN size has been shown, and based on previously reported reductions in LGN volumes in human albinism, we suggest that fiber projections from LGN to the primary visual cortex (V1) are also reduced. Studying structural differences in the visual system of albinism can improve the understanding of the mechanism of misrouting and subsequent clinical applications. Diffusion data and tractography are useful for mapping the OR (optic radiation). This manuscript describes two algorithms for OR reconstruction in order to compare brain connectivity in albinism and controls.An MRI scanner with a 32-channel head coil was used to acquire structural scans. A T1-weighted 3D-MPRAGE sequence with 1 mm(3) isotropic voxel size was used to generate high-resolution images for V1 segmentation. Multiple proton density (PD) weighted images were acquired coronally for right and left LGN localization. Diffusion tensor imaging (DTI) scans were acquired with 64 diffusion directions. Both deterministic and probabilistic tracking methods were run and compared, with LGN as the seed mask and V1 as the target mask. Though DTI provides relatively poor spatial resolution, and accurate delineation of OR may be challenging due to its low fiber density, tractography has been shown to be advantageous both in research and clinically. Tract based spatial statistics (TBSS) revealed areas of significantly reduced white matter integrity within the OR in patients with albinism compared to controls. Pairwise comparisons revealed a significant reduction in LGN to V1 connectivity in albinism compared to controls. Comparing both tracking algorithms revealed common findings, strengthening the reliability of the technique.