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Michael R Ibbotson - One of the best experts on this subject based on the ideXlab platform.

  • contrast and temporal frequency related adaptation in the pretectal nucleus of the Optic Tract
    Journal of Neurophysiology, 2005
    Co-Authors: Michael R Ibbotson
    Abstract:

    In mammals, many cells in the retino-geniculate-cortical pathway adapt during stimulation with high contrast gratings. In the visual cortex, adaptation to high contrast images reduces sensitivity at low contrasts while only moderately affecting sensitivity at high contrasts, thus generating rightward shifts in the contrast response functions (contrast gain control). Similarly, motion adaptation at particular temporal frequencies (TFs) alters the temporal tuning properties of cortical cells. For the first time in any species, this paper investigates the influence of motion adaptation on both the contrast and TF responses of neurons in the retino-pretectal pathway by recording from direction-selective neurons in the nucleus of the Optic Tract (NOT) of the marsupial wallaby, Macropus eugenii. This species is of interest because its NOT receives almost all input directly from the retina, with virtually none from the visual cortex (unlike cats and primates). All NOT cells show changes in their contrast response functions after adaptation, many revealing contrast gain control. Contrast adaptation is direction-dependent, preferred directions producing the largest changes. The lack of cortical input suggests that contrast adaptation is generated independently from the cortex in the NOT or retina. Motion adaptation also produces direction-selective effects on the TF tuning of NOT neurons by shifting the location of the optimum TF. Cells that show strong adaptation to contrast also tend to show large changes in TF tuning, suggesting similar intracellular mechanisms. The data are discussed in terms of the generality of contrast adaptation across mammalian species and across unconnected brain regions within the same species.

  • adaptation to visual motion in directional neurons of the nucleus of the Optic Tract
    Journal of Neurophysiology, 1998
    Co-Authors: Michael R Ibbotson, Colin W G Clifford, R F Mark
    Abstract:

    Ibbotson, Michael R., Colin W. G. Clifford, and Richard F. Mark. Adaptation to visual motion in directional neurons of the nucleus of the Optic Tract. J. Neurophysiol. 79: 1481–1493, 1998. Extracel...

  • spatiotemporal response properties of direction selective neurons in the nucleus of the Optic Tract and dorsal terminal nucleus of the wallaby macropus eugenii
    Journal of Neurophysiology, 1994
    Co-Authors: Michael R Ibbotson, R F Mark, Ted Maddess
    Abstract:

    1. The spatial and temporal response characteristics of direction-selective neurons in the nucleus of the Optic Tract and dorsal terminal nucleus of the accessory Optic system (NOT-DTN) of the wall...

Akira Yamaura - One of the best experts on this subject based on the ideXlab platform.

  • histologic characteristics of normal perivascular spaces along the Optic Tract new pathogenetic mechanism for edema in tumors in the pituitary region
    American Journal of Neuroradiology, 2004
    Co-Authors: Naokatsu Saeki, Yoshio Uchino, Hisayuki Murai, Motoo Kubota, Yuichiro Nagai, Iichiro Matsuura, Hiroshi Ishikura, Hiroo Ikehira, Akira Yamaura
    Abstract:

    BACKGROUND AND PURPOSE: Perivascular (PV) spaces are known to distend and cause edema along the Optic Tract (OT) in pituitary-region tumors. Interstitial fluid may be retained in PV spaces when tumors block their drainage outlets to subarachnoid spaces. However, these spaces and their outlets have not been anatomically elucidated. Our purpose was to evaluate how often large PV spaces are present along the OT and demonstrate their superficial communication points to adjacent subarachnoid spaces. METHODS: We examined serial histologic sections of 10 hemispheric blocks obtained from cadavers without cerebral abnormality. RESULTS: Large PV spaces, 0.5–1.5 mm in maximum height, were always present along the middle portion of the OT. Perforation points of the largest spaces were noted at the medial sulcus of the OT in seven hemispheres and through the OT in three. CONCLUSION: Large PV spaces are present along the middle portion of the OT. Their communication point to adjacent subarachnoid spaces was histologically demonstrated. The locations and variations of the outlet of large PV spaces explain the clinical features of edemas; these findings anatomically support the hypothesis that blockage of the outlets to subarachnoid spaces may play a role in distending the PV spaces and in causing edema in pituitary-region tumors. Only MR imaging has revealed this change; further pathologic investigations are awaited.

  • mr imaging study of edema like change along the Optic Tract in patients with pituitary region tumors
    American Journal of Neuroradiology, 2003
    Co-Authors: Naokatsu Saeki, Yoshio Uchino, Hisayuki Murai, Motoo Kubota, Kouichi Isobe, Takashi Uno, Kenro Sunami, Akira Yamaura
    Abstract:

    BACKGROUND AND PURPOSE: Edema-like change along the Optic Tract commonly occurs in association with craniopharyngiomas. The aim of this study was to clarify whether it occurs in association with other common pituitary region tumors and to elucidate its mechanism as seen on MR images. METHODS: Fifty patients with pituitary region tumors that were touching or compressing the Optic pathway underwent heavily T2-weighted MR imaging before and after treatment. RESULTS: Edema-like change along the Optic Tract was visible on the images of four of 25 pituitary adenomas, eight of 11 craniopharyngiomas, one germ cell tumor, and one malignant lymphoma and was not visible on the images of seven meningiomas and five Rathke’s cleft cysts. After therapeutic decompression of the Optic pathway, the edema-like change disappeared and large Virchow-Robin spaces, present under normal conditions, became visible along the Optic Tract. Comparison of pre- and post-treatment coronal and axial view MR images revealed that the edema-like change had been located at, along, and/or around the large Virchow-Robin spaces along the Optic Tract. CONCLUSION: Edema-like change occurs in association with pituitary region tumors other than craniopharyngiomas. It is related with distension of normally present large Virchow-Robin spaces adjacent to the Optic Tract. Because Virchow-Robin spaces are speculated to be a drainage route of interstitial fluid into the subarachnoid space, their distension may be related to the fluid retention in and along the Virchow-Robin spaces, the outlet of which into the subpial and/or subarachnoid space(s) is blocked by pituitary region tumors.

Holly Bridge - One of the best experts on this subject based on the ideXlab platform.

  • Optic Tract shrinkage limits visual restoration after occipital stroke
    Stroke, 2021
    Co-Authors: Berkeley K Fahrenthold, Holly Bridge, Matthew R Cavanaugh, Subin Jang, Allison J Murphy, Sara Ajina, Krystel R Huxlin
    Abstract:

    BACKGROUND AND PURPOSE Damage to the adult primary visual cortex (V1) causes vision loss in the contralateral visual hemifield, initiating a process of trans-synaptic retrograde degeneration. The present study examined functional implications of this process, asking if degeneration impacted the amount of visual recovery attainable from visual restoration training in chronic patients, and if restoration training impacted Optic Tract (OT) shrinkage. METHODS Magnetic resonance imaging was used to measure OT volumes bilaterally in 36 patients with unilateral occipital stroke. From OT volumes, we computed laterality indices (LI), estimating the stroke-induced OT shrinkage in each case. A subset of these chronic patients (n=14, 13±6 months poststroke) underwent an average of nearly 1 year of daily visual restoration training, which repeatedly stimulated vision in their blind field. The amount of visual field recovery was quantified using Humphrey perimetry, and post training magnetic resonance imaging was used to assess the impact of training on OT shrinkage. RESULTS OT LI was correlated with time since stroke: it was close to 0 (no measurable OT shrinkage) in subacute participants ( 6 months poststroke) exhibited LI >0, but with significant variability. Visual training did not systematically alter LI, but chronic patients with baseline LI≈0 (no OT shrinkage) exhibited greater visual field recovery than those with LI>0. CONCLUSIONS Unilateral OT shrinkage becomes detectable with magnetic resonance imaging by ≈7 months poststroke, albeit with significant interindividual variability. Although visual restoration training did not alter the amount of degeneration already sustained, OT shrinkage appeared to serve as a biomarker of the potential for training-induced visual recovery in chronic cortically blind patients.

  • quantifying the pattern of Optic Tract degeneration in human hemianopia
    Journal of Neurology Neurosurgery and Psychiatry, 2014
    Co-Authors: Rebecca S Millington, Panitha Jindahra, John L Barbur, Gordon T Plant, Clarissa L Yasuda, Mark Jenkinson, Christopher Kennard, Fernando Cendes, Holly Bridge
    Abstract:

    Background The existence of transsynaptic retrograde degeneration (TRD) in the human visual system has been established, however the dependence of TRD on different factors such as lesion location, size and manner of lesion acquisition has yet to be quantified. Methods We obtained T1-weighted structural and diffusion-weighted images for 26 patients with adult-acquired or congenital hemianopia and 12 age-matched controls. The Optic Tract (OT) was defined and measured in the structural and diffusion-weighted images, and degeneration assessed by comparing the integrity of Tracts in the lesioned and in the undamaged hemisphere. Results OT degeneration was found in all patients with established lesions, regardless of lesion location. In patients with acquired lesions, the larger the initial lesion, the greater is the resulting TRD. However, this was not the case for congenital patients, who generally showed greater degeneration than would be predicted by lesion size. A better predictor of TRD was the size of the visual field deficit, which was correlated with degeneration across all patients. Interestingly, although diffusion-weighted imaging (DWI) is more frequently used to examine white matter Tracts, in this study the T1-weighted scans gave a better indication of the extent of Tract degeneration. Conclusions We conclude that TRD of the OT occurs in acquired and congenital hemianopia, is correlated with visual field loss, and is most severe in congenital cases. Understanding the pattern of TRD may help to predict effects of any visual rehabilitation training.

  • imaging reveals Optic Tract degeneration in hemianopia
    Investigative Ophthalmology & Visual Science, 2011
    Co-Authors: Holly Bridge, Panitha Jindahra, John L Barbur, Gordon T Plant
    Abstract:

    PURPOSE. To investigate whether there is transsynaptic degeneration in the human Optic Tract in hemianopia. To consider how the degeneration varies with duration of hemianopia and location of insult. METHODS. Seven patients with damage to the primary visual cortex (V1), the lateral geniculate nucleus (LGN), or the Optic Tract were scanned with structural MRI. The volume and crosssectional area of the left and right Optic Tracts were computed based on the intensity values of the T1-weighted image. High values correspond to voxels with high white matter content, and the values decrease as the white matter content drops (indicating degeneration). A laterality index to compare the Tract size in the two hemispheres was calculated at different intensity values. RESULTS. The three hemianopic patients with longstanding damage to either V1 or LGN showed laterality indices greater than 0.5 at the highest intensity values, indicating significant Optic Tract degeneration. Those with recent damage to the Optic Tract had even higher laterality indices due to direct degeneration. Even 18 months after V1 lesion, there was a significant correlation between the cross-section and volume indices at different intensity thresholds, whereas no control subject showed any correlation. CONCLUSIONS. Transsynaptic degeneration had already begun 18 months after lesion. Although there was no visible decrease in volume at this stage, the white matter integrity was compromised. Significant decrease in volume could be visualized at longer durations of hemianopia. This method of objectively assessing structural images provides an effective, noninvasive approach to monitor the timescale of Optic Tract degeneration. (Invest Ophthalmol Vis Sci. 2011;52:382‐388) DOI:10.1167/ iovs.10-5708

  • pod10 demonstration of Optic Tract atrophy in hemianopia by magnetic resonance imaging confirmation of retrograde trans synaptic degeneration in the human visual pathway
    Journal of Neurology Neurosurgery and Psychiatry, 2010
    Co-Authors: Gordon T Plant, John L Barbur, Panitha Jindahra, Holly Bridge
    Abstract:

    Degeneration of retinal ganglion cells in acquired hemianopia (HH) has been shown using Optical coherence tomography. We hypothesise that change in the ipsilesional Optic Tract (OT) should be found using MR imaging. Three cases of HH for >10 years, two for

Naokatsu Saeki - One of the best experts on this subject based on the ideXlab platform.

  • histologic characteristics of normal perivascular spaces along the Optic Tract new pathogenetic mechanism for edema in tumors in the pituitary region
    American Journal of Neuroradiology, 2004
    Co-Authors: Naokatsu Saeki, Yoshio Uchino, Hisayuki Murai, Motoo Kubota, Yuichiro Nagai, Iichiro Matsuura, Hiroshi Ishikura, Hiroo Ikehira, Akira Yamaura
    Abstract:

    BACKGROUND AND PURPOSE: Perivascular (PV) spaces are known to distend and cause edema along the Optic Tract (OT) in pituitary-region tumors. Interstitial fluid may be retained in PV spaces when tumors block their drainage outlets to subarachnoid spaces. However, these spaces and their outlets have not been anatomically elucidated. Our purpose was to evaluate how often large PV spaces are present along the OT and demonstrate their superficial communication points to adjacent subarachnoid spaces. METHODS: We examined serial histologic sections of 10 hemispheric blocks obtained from cadavers without cerebral abnormality. RESULTS: Large PV spaces, 0.5–1.5 mm in maximum height, were always present along the middle portion of the OT. Perforation points of the largest spaces were noted at the medial sulcus of the OT in seven hemispheres and through the OT in three. CONCLUSION: Large PV spaces are present along the middle portion of the OT. Their communication point to adjacent subarachnoid spaces was histologically demonstrated. The locations and variations of the outlet of large PV spaces explain the clinical features of edemas; these findings anatomically support the hypothesis that blockage of the outlets to subarachnoid spaces may play a role in distending the PV spaces and in causing edema in pituitary-region tumors. Only MR imaging has revealed this change; further pathologic investigations are awaited.

  • mr imaging study of edema like change along the Optic Tract in patients with pituitary region tumors
    American Journal of Neuroradiology, 2003
    Co-Authors: Naokatsu Saeki, Yoshio Uchino, Hisayuki Murai, Motoo Kubota, Kouichi Isobe, Takashi Uno, Kenro Sunami, Akira Yamaura
    Abstract:

    BACKGROUND AND PURPOSE: Edema-like change along the Optic Tract commonly occurs in association with craniopharyngiomas. The aim of this study was to clarify whether it occurs in association with other common pituitary region tumors and to elucidate its mechanism as seen on MR images. METHODS: Fifty patients with pituitary region tumors that were touching or compressing the Optic pathway underwent heavily T2-weighted MR imaging before and after treatment. RESULTS: Edema-like change along the Optic Tract was visible on the images of four of 25 pituitary adenomas, eight of 11 craniopharyngiomas, one germ cell tumor, and one malignant lymphoma and was not visible on the images of seven meningiomas and five Rathke’s cleft cysts. After therapeutic decompression of the Optic pathway, the edema-like change disappeared and large Virchow-Robin spaces, present under normal conditions, became visible along the Optic Tract. Comparison of pre- and post-treatment coronal and axial view MR images revealed that the edema-like change had been located at, along, and/or around the large Virchow-Robin spaces along the Optic Tract. CONCLUSION: Edema-like change occurs in association with pituitary region tumors other than craniopharyngiomas. It is related with distension of normally present large Virchow-Robin spaces adjacent to the Optic Tract. Because Virchow-Robin spaces are speculated to be a drainage route of interstitial fluid into the subarachnoid space, their distension may be related to the fluid retention in and along the Virchow-Robin spaces, the outlet of which into the subpial and/or subarachnoid space(s) is blocked by pituitary region tumors.

Sonal Jhaveri - One of the best experts on this subject based on the ideXlab platform.

  • early postnatal expression of l1 by retinal fibers in the Optic Tract and synaptic targets of the syrian hamster
    The Journal of Comparative Neurology, 2000
    Co-Authors: Alvin W Lyckman, Kenneth L Moya, Annamaria Confaloni, Sonal Jhaveri
    Abstract:

    Previous immunohistochemical studies in mouse, rat, and chick have reported that the expression of the glycoprotein and cell adhesion molecule L1, a member of the immunoglobulin superfamily, shows regulation during development of retina and Optic nerve. To extend our understanding of the role of L1 in developing neural circuitry, we have examined L1 expression in the Optic Tract and thalamic and midbrain synaptic targets of retinal fibers in the early postnatal Syrian hamster, a well-characterized developmental model of the primary visual projection. Metabolic labeling studies reveal that a synaptically targeted, sulfated, and glycosylated form of L1 undergoes rapid axonal transport from the retina. Retinofugal transport of L1 decreases commensurate with the decline in immunoreactivity of retinal fibers in the visual pathway. Retinal ganglion cell axons show intense L1 immunoreactivity as they navigate in highly fasciculated bundles in the Optic Tract overlying the lateral geniculate body and in the superior colliculus. We found no evidence of L1 immunoreactivity on retinal axon collaterals as they defasciculate from the Optic Tract and branch into target neuropils. L1 immunoreactivity wanes in Optic Tract as axon terminal arbors are elaborated in the lateral geniculate body and superior colliculus and as myelination in the visual pathway commences. This pattern of L1 expression suggests that, in the early postnatal period, L1 may support fasciculation of retinal fibers, maintaining them within the Optic Tract, and that subsequent down-regulation of L1 may facilitate their terminal arborization and myelination.

  • oligodendrocytes and myelin formation along the Optic Tract of the developing hamster an immunohistochemical study using the rip antibody
    Glia, 1992
    Co-Authors: Sonal Jhaveri, Reha S Erzurumlu, Beth Friedman, Gerald E Schneider
    Abstract:

    The monoclonal antibody Rip recognizes an antigen specific to oligoderdrocytes and their processes (Friedman et al: Gila 2:380, 1989). We have used this antibody to document the appearance of oligodendrocytes and the sequence of ensheathment of axons along the Optic Tract (OT) and within its major target areas in neonatal (P3–P21) and adult hamsters. Myelination of axons in the visual pathway follows an overall proximo-distal gradient. On P3, immunopositive, pre-ensheathing oligodendrocytes are detected in the OT ventral to the lateral geniculate body (LGB) whereas myelin segments are present around OT axons by P5. The first pre-ensheathing oligodendrocytes are detected medially in the LGB on P7 and myelinated axons in the overlying OT by P11. In the superior colliculus, pre-ensheathing oligodendrocytes are prsent in the Optic fiber layer (SO) on P7, but not in the superficial gray layer (SGS) until P11. Myelination of axons within SO proceeds along a marked rostro-caudal gradient. On P14, axons in rostral SO are heavily myelinated; thereafter, ensheathment continues caudally within the SO and the SGS. The progressive invasion of oligodendrocytes along the proximo-distal axis of the Optic pathway, and the corresponding myelination of OT axons, are discussed in the context of a possible inhibitory role of oligodendrocytes in regulating the regenerative propensity of retinotectal axons. © 1992 Wiley-Liss, Inc.