-
Continuum (Minneapolis, Minn.) Aug 2014Building on the anatomic and diagnostic approaches presented elsewhere in this issue of CONTINUUM, this article presents important differential considerations for... (Review)
Review
PURPOSE OF REVIEW
Building on the anatomic and diagnostic approaches presented elsewhere in this issue of CONTINUUM, this article presents important differential considerations for chiasmal and retrochiasmal vision loss, useful strategies for confirming the underlying etiology, principles of their natural history, and, where appropriate, treatment strategies.
RECENT FINDINGS
Although a wide variety of pathologic processes can affect the optic chiasm and retrochiasmal visual pathways, those commonly seen in neurologic practice are comparatively fewer in number. This article updates current understanding of vision loss localizing to the optic chiasm, including pituitary adenoma, sellar meningiomas, and aneurysms. Important causes of retrochiasmal vision loss, including stroke and posterior reversible encephalopathy syndrome, are also presented.
SUMMARY
The optic chiasm and retrochiasmal visual pathways are susceptible to various forms of injury, with resultant patterns of vision loss that can be precisely localized on the basis of clinical and neuroimaging findings. Accurate localization, in association with other clinical features, allows for consideration of relevant differential diagnoses, which can be confirmed through the judicious application of appropriate diagnostic studies. Accurate localization, diagnosis, and robust clinical surveillance are essential to the effective management and treatment of these causes of vision loss.
Topics: Adult; Blindness; Female; Humans; Male; Middle Aged; Optic Chiasm; Pituitary Diseases; Stroke; Visual Pathways
PubMed: 25099100
DOI: 10.1212/01.CON.0000453312.37143.d2 -
Visual Neuroscience Nov 2013The notion of a set of neurons that form a "bridge locus" serving as the immediate substrate of visual perception is examined in the light of evidence on the... (Review)
Review
The notion of a set of neurons that form a "bridge locus" serving as the immediate substrate of visual perception is examined in the light of evidence on the architecture of the visual pathway, of current thinking about perceptual representations, and of the basis of perceptual awareness. The bridge locus is likely to be part of a tangled web of representations, and this complexity raises the question of whether another scheme that relies less on geography might offer a better framework. The bridge locus bears a close relationship to the neural correlate of consciousness (NCC), and like the NCC may be a concept which is no longer precise enough to provide a useful basis for reasoning about the relationship between brain activity and perceptual experience.
Topics: Consciousness; Humans; Visual Cortex; Visual Pathways; Visual Perception
PubMed: 24476967
DOI: 10.1017/S0952523813000527 -
The Journal of Physiology Jul 2005Parallel processing streams in the primate visual system originate from more than a dozen anatomically and functionally distinct types of retinal ganglion cells (RGCs).... (Review)
Review
Parallel processing streams in the primate visual system originate from more than a dozen anatomically and functionally distinct types of retinal ganglion cells (RGCs). A central problem in determining how visual information is processed is understanding how each of these RGC types connects to more central structures, including the lateral geniculate nucleus (LGN) of the thalamus and (via the LGN) the primary visual cortex. Nevertheless, the available functional and anatomical evidence linking together specific cell types across these structures is surprisingly indirect. This review evaluates the available evidence and assesses the strength of the many inferences that can be made from these observations. There is strong evidence that parasol RGCs are the provenance of the magnocellular (M) visual pathway and that midget RGCs give rise to the parvocellular (P) pathway. Furthermore, the M and P pathways remain segregated up to the input layer of primary visual cortex. The relationships between the numerous other RGC types and cell types in the LGN remain less certain. and there remains ambiguity about how best to define additional pathways, such as the koniocellular (K) pathway, which probably arise from these other, less common, RGC types.
Topics: Action Potentials; Animals; Models, Neurological; Nerve Net; Primates; Retinal Ganglion Cells; Visual Cortex; Visual Pathways; Visual Perception
PubMed: 15905213
DOI: 10.1113/jphysiol.2005.088047 -
The Journal of Physiology Aug 19911. Light-induced phase shifts of the circadian rhythm of wheel-running activity were used to measure the photic sensitivity of a circadian pacemaker and the visual...
1. Light-induced phase shifts of the circadian rhythm of wheel-running activity were used to measure the photic sensitivity of a circadian pacemaker and the visual pathway that conveys light information to it in the golden hamster (Mesocricetus auratus). The sensitivity to stimulus irradiance and duration was assessed by measuring the magnitude of phase-shift responses to photic stimuli of different irradiance and duration. The visual sensitivity was also measured at three different phases of the circadian rhythm. 2. The stimulus-response curves measured at different circadian phases suggest that the maximum phase-shift is the only aspect of visual responsivity to change as a function of the circadian day. The half-saturation constants (sigma) for the stimulus-response curves are not significantly different over the three circadian phases tested. The photic sensitivity to irradiance (1/sigma) appears to remain constant over the circadian day. 3. The hamster circadian pacemaker and the photoreceptive system that subserves it are more sensitive to the irradiance of longer-duration stimuli than to irradiance of briefer stimuli. The system is maximally sensitive to the irradiance of stimuli of 300 s and longer in duration. A quantitative model is presented to explain the changes that occur in the stimulus-response curves as a function of photic stimulus duration. 4. The threshold for photic stimulation of the hamster circadian pacemaker is also quite high. The threshold irradiance (the minimum irradiance necessary to induce statistically significant responses) is approximately 10(11) photons cm-2 s-1 for optimal stimulus durations. This threshold is equivalent to a luminance at the cornea of 0.1 cd m-2. 5. We also measured the sensitivity of this visual pathway to the total number of photons in a stimulus. This system is maximally sensitive to photons in stimuli between 30 and 3600 s in duration. The maximum quantum efficiency of photic integration occurs in 300 s stimuli. 6. These results suggest that the visual pathways that convey light information to the mammalian circadian pacemaker possess several unique characteristics. These pathways are relatively insensitive to light irradiance and also integrate light inputs over relatively long durations. This visual system, therefore, possesses an optimal sensitivity of 'tuning' to total photons delivered in stimuli of several minutes in duration. Together these characteristics may make this visual system unresponsive to environmental 'noise' that would interfere with the entrainment of circadian rhythms to light-dark cycles.
Topics: Animals; Biological Clocks; Circadian Rhythm; Cricetinae; Dose-Response Relationship, Radiation; Light; Male; Mathematics; Mesocricetus; Motor Activity; Photic Stimulation; Visual Pathways
PubMed: 1895235
DOI: 10.1113/jphysiol.1991.sp018660 -
Current Biology : CB Jan 2022Three of the most robust functional landmarks in the human brain are the selective responses to faces in the fusiform face area (FFA), scenes in the parahippocampal...
Three of the most robust functional landmarks in the human brain are the selective responses to faces in the fusiform face area (FFA), scenes in the parahippocampal place area (PPA), and bodies in the extrastriate body area (EBA). Are the selective responses of these regions present early in development or do they require many years to develop? Prior evidence leaves this question unresolved. We designed a new 32-channel infant magnetic resonance imaging (MRI) coil and collected high-quality functional MRI (fMRI) data from infants (2-9 months of age) while they viewed stimuli from four conditions-faces, bodies, objects, and scenes. We find that infants have face-, scene-, and body-selective responses in the location of the adult FFA, PPA, and EBA, respectively, powerfully constraining accounts of cortical development.
Topics: Adult; Brain; Brain Mapping; Humans; Magnetic Resonance Imaging; Pattern Recognition, Visual; Photic Stimulation; Visual Pathways
PubMed: 34784506
DOI: 10.1016/j.cub.2021.10.064 -
Arquivos Brasileiros de Oftalmologia 2011The pattern electroretinogram is an electrophysiological test that assesses the function of inner retinal layers, particularly the ganglion cells layer of retina, using... (Review)
Review
The pattern electroretinogram is an electrophysiological test that assesses the function of inner retinal layers, particularly the ganglion cells layer of retina, using a reversing checkerboard or grating pattern that produces no change in average luminance over time. The normal pattern electroretinogram is composed of a proeminent positive component (P50) and a large later negative component (N95). Since structural damage that compromises the retinal ganglion cell layer can lead to pattern electroretinogram changes, particularly in the N95 amplitude, the test can be useful in the treatment of a number of anterior visual pathway diseases. In this article, we review the methods for recording pattern electroretinogram and its usefulness in the diagnosis and management of diseases including inflammatory, hereditary, ischemic and compressive lesions of the anterior visual pathway.
Topics: Electroretinography; Humans; Optic Nerve Diseases; Visual Pathways
PubMed: 21915454
DOI: 10.1590/s0004-27492011000300017 -
Scientific Reports Mar 2023Macular degeneration (MD) embodies a collection of disorders causing a progressive loss of central vision. Cross-sectional MRI studies have revealed structural changes...
Macular degeneration (MD) embodies a collection of disorders causing a progressive loss of central vision. Cross-sectional MRI studies have revealed structural changes in the grey and white matter in the posterior visual pathway in MD but there remains a need to understand how such changes progress over time. To that end we assessed the posterior pathway, characterising the visual cortex and optic radiations over a ~ 2-year period in MD patients and controls. We performed cross-sectional and longitudinal analysis of the former. Reduced cortical thickness and white matter integrity were observed in patients compared to controls, replicating previous findings. While faster, neither the rate of thinning in visual cortex nor the reduction in white matter integrity during the ~ 2-year period reached significance. We also measured cortical myelin density; cross-sectional data showed this was higher in patients than controls, likely as a result of greater thinning of non-myelinated tissue in patients. However, we also found evidence of a greater rate of loss of myelin density in the occipital pole in the patient group indicating that the posterior visual pathway is at risk in established MD. Taken together, our results revealed a broad decline in grey and white matter in the posterior visual pathway in bilateral MD; cortical thickness and fractional anisotropy show hints of an accelerated rate of loss also, with larger effects emerging in the occipital pole.
Topics: Humans; Visual Pathways; Cross-Sectional Studies; Magnetic Resonance Imaging; Occipital Lobe; White Matter; Macular Degeneration
PubMed: 36973337
DOI: 10.1038/s41598-023-31819-x -
Clinical Neurophysiology : Official... May 2024To explore associations of the main component (P100) of visual evoked potentials (VEP) to pre- and postchiasmatic damage in multiple sclerosis (MS).
OBJECTIVE
To explore associations of the main component (P100) of visual evoked potentials (VEP) to pre- and postchiasmatic damage in multiple sclerosis (MS).
METHODS
31 patients (median EDSS: 2.5), 13 with previous optic neuritis (ON), and 31 healthy controls had VEP, optical coherence tomography and magnetic resonance imaging. We tested associations of P100-latency to the peripapillary retinal nerve fiber layer (pRNFL), ganglion cell/inner plexiform layers (GCIPL), lateral geniculate nucleus volume (LGN), white matter lesions of the optic radiations (OR-WML), fractional anisotropy of non-lesional optic radiations (NAOR-FA), and to the mean thickness of primary visual cortex (V1). Effect sizes are given as marginal R (mR).
RESULTS
P100-latency, pRNFL, GCIPL and LGN in patients differed from controls. Within patients, P100-latency was significantly associated with GCIPL (mR = 0.26), and less strongly with OR-WML (mR = 0.17), NAOR-FA (mR = 0.13) and pRNFL (mR = 0.08). In multivariate analysis, GCIPL and NAOR-FA remained significantly associated with P100-latency (mR = 0.41). In ON-patients, P100-latency was significantly associated with LGN volume (mR = -0.56).
CONCLUSIONS
P100-latency is affected by anterior and posterior visual pathway damage. In ON-patients, damage at the synapse-level (LGN) may additionally contribute to latency delay.
SIGNIFICANCE
Our findings corroborate post-chiasmatic contributions to the VEP-signal, which may relate to distinct pathophysiological mechanisms in MS.
Topics: Humans; Male; Female; Geniculate Bodies; Adult; Evoked Potentials, Visual; Visual Pathways; Middle Aged; Multiple Sclerosis; Tomography, Optical Coherence; Magnetic Resonance Imaging; Optic Neuritis
PubMed: 38461596
DOI: 10.1016/j.clinph.2024.02.020 -
Cell Reports Oct 2018In the primate visual system, direction-selective (DS) neurons are critical for visual motion perception. While DS neurons in the dorsal visual pathway have been well...
In the primate visual system, direction-selective (DS) neurons are critical for visual motion perception. While DS neurons in the dorsal visual pathway have been well characterized, the response properties of DS neurons in other major visual areas are largely unexplored. Recent optical imaging studies in monkey visual cortex area 2 (V2) revealed clusters of DS neurons. This imaging method facilitates targeted recordings from these neurons. Using optical imaging and single-cell recording, we characterized detailed response properties of DS neurons in macaque V2. Compared with DS neurons in the dorsal areas (e.g., middle temporal area [MT]), V2 DS neurons have a smaller receptive field and a stronger antagonistic surround. They do not code speed or plaid motion but are sensitive to motion contrast. Our results suggest that V2 DS neurons play an important role in figure-ground segregation. The clusters of V2 DS neurons are likely specialized functional systems for detecting motion contrast.
Topics: Animals; Macaca fascicularis; Motion Perception; Visual Pathways; Visual Perception
PubMed: 30282025
DOI: 10.1016/j.celrep.2018.09.014 -
Nature Reviews. Neuroscience Apr 2011The division of cortical visual processing into distinct dorsal and ventral streams is a key framework that has guided visual neuroscience. The characterization of the... (Review)
Review
The division of cortical visual processing into distinct dorsal and ventral streams is a key framework that has guided visual neuroscience. The characterization of the ventral stream as a 'What' pathway is relatively uncontroversial, but the nature of dorsal stream processing is less clear. Originally proposed as mediating spatial perception ('Where'), more recent accounts suggest it primarily serves non-conscious visually guided action ('How'). Here, we identify three pathways emerging from the dorsal stream that consist of projections to the prefrontal and premotor cortices, and a major projection to the medial temporal lobe that courses both directly and indirectly through the posterior cingulate and retrosplenial cortices. These three pathways support both conscious and non-conscious visuospatial processing, including spatial working memory, visually guided action and navigation, respectively.
Topics: Animals; Attention; Brain Mapping; Consciousness; Humans; Space Perception; Visual Cortex; Visual Pathways
PubMed: 21415848
DOI: 10.1038/nrn3008