Tests of the limiting visual resolution of the DCMD system of the lubber grasshopper to rectangular gratings

Visual acuity measurements using the descending contralateral movement detector (DCMD) neuron in the lubber grasshopper, Romalea microptera, show responses to spatial angles as small as 0.3°. Moving, black-white striped objects were viewed on a rear-projection screen.Nonuniformity and spatial sub-harmonic measurements of the object patterns showed that any artifacts which were present were below the resolution limits of the human visual system (and presumably that of Romalea).Nonstationarity in the responses of the DCMD system can be categorized as long-term (sensitivity changes) and short term (habituation). A mathematical model for habituation is used to illustrate how confidence in responses may be lost due to the incorporation of too many samples of habituated data.     

Narrowband gamma oscillations propagate and synchronize throughout the mouse thalamocortical visual system

1. Download : Download high-res image (243KB)
2. Download : Download full-size image

     

Spatial modulation of dark versus bright stimulus responses in the mouse visual system

1. Download : Download high-res image (156KB)
2. Download : Download full-size image

     

Instructive effect of visual experience in mouse visual cortex

We describe a form of experience-dependent response enhancement in the visual cortex of awake mice. Repeated presentations of grating stimuli of a single orientation result in a persistent enhancement of responses evoked by the test stimulus. Response potentiation is specific to the orientation of the test stimulus, develops gradually over the course of several training sessions, and occurs in both juvenile and adult mice. The stimulus-selective response potentiation (SRP) can mask deprivation-induced response depression in adult mice. SRP requires NMDA receptor activation and is prevented by viral delivery of a peptide that interferes with AMPA receptor trafficking. SRP may reveal the mechanisms involved in certain forms of perceptual learning.     

Representational drift in the mouse visual cortex

1. Download : Download high-res image (157KB)
2. Download : Download full-size image

     

Adaptation of the visual system

We recorded the total pulse response of the optic nerve in frogs to varying degrees of increase and decrease of light from the original adapting level. On the basis of these data, we plotted curves of dependence of the magnitude of response on the logarithm of relative value of increase and decrease of light (the amplitude characteristic — AC). The AC is steepest in the zone of adapting background and sloped on either side of it. It follows that under stationary conditions of illumination, the eye is capable of finely differentiating light intensity only within a narrow range (one logarithmic unit). After adaptation to a new level of illumination, the AC shifts along the scale of light intensity in such a way that the steepest portion corresponds to the adapting brightness. Increase in steepness of the AC occurs precisely during the process of adaptation. The contrast sensitivity of the human visual system is greatest near the adapting level and declines on either side of it. It follows that in man steepness of the visual system AC is greatest in the zone of the adapting background. Both increase and decrease of intensity of the adapting background are accompanied by a decline of contrast sensitivity, which rises again during the process of adaptation to a new level. Thanks to adaptive shift of the steep portion of the AC along the scale of light intensity, a visual system having a high contrast sensitivity only within a narrow "working" range is capable of finely differentiating light intensity in significantly changing conditions of illumination.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 81–89, July–August, 1969.     

Melanopsin regulates visual processing in the mouse retina

The discovery of melanopsin-dependent inner retinal photoreceptors in mammals has precipitated a fundamental reassessment of such non-image forming (NIF) light responses as circadian photoentrainment and the pupil light reflex. By contrast, it remains unclear whether these new photoreceptors also play a role in classical image-forming vision. The retinal ganglion cells that subserve inner retinal photoreception (ipRGCs) project overwhelmingly to brain areas involved in NIF responses, indicating that, in terms of central signaling, their predominant function is non-image forming. However, ipRGCs also exhibit intraretinal communication via gap junction coupling, which could allow them to modulate classical visual pathways within this tissue. Here, we explore this second possibility by using melanopsin knockout (Opn4-/-) mice to examine the role of inner retinal photoreceptors in diurnal regulation of retinal function. By using electroretinography in wild-type mice, we describe diurnal rhythms in both the amplitude and speed of the retinal cone pathway that are a function of both prior light exposure and circadian phase. Unexpectedly, loss of the melanopsin gene abolishes circadian control of these parameters, causing significant attenuation of the diurnal variation in cone vision. Our results demonstrate for the first time a melanopsin-dependent regulation of visual processing within the retina, revealing an important function for inner retinal photoreceptors in optimizing classical visual pathways according to time of day.     

The visual system of the alligator

The eye tissues and liver of the alligator contain vitamin A₁ alone. The retina contains rhodopsin, typical in absorption spectrum (λ_max 500 mµ); but synthesized in solution from neo-b retinene and opsin much more rapidly than are the frog, mammalian, or chicken rhodopsins previously examined. In this regard alligator rhodopsin resembles the rhodopsins and porphyropsins of fishes, all of which so far investigated are synthesized rapidly in solution. The rates of synthesis in vitro of frog and alligator rhodopsins are matched closely by the rates of rod dark adaptation in living frogs and alligators, measured electrophysiologically at the same temperature. Alligator rods dark-adapt, and alligator rhodopsin is synthesized in solution, at rates characteristically associated with cones and cone pigments in frogs, mammals, and birds.     

The scale of the visual pathways of mouse and rat

Photoreceptors and neurons at various levels to cortex have been counted in mouse and rat. The ratios of neuron numbers (rat/mouse) are similar to the ratio of retinal areas or the squared ratio of eye sizes; so to a first approximation the two species have linearly scaled eyes, equal photoreceptor spacings (in m), and visual pathways scaled numerically by the number of photoreceptors. With supplementary data from the literature, some of the functional implications of the design can be evaluated level by level. Overall, there is structural and computational economy, or even parsimony.     

Apoptosis in the developing visual system

Programmed cellular death is a widespread phenomenon during development of the nervous system. Two classes of molecules are particularly important in the context of apoptosis control in the nervous system: intracellular effectors homologous to the Caenorhabditis elegans Ced-3, -4, and -9 proteins, which in mammals correspond to the proteases of the caspase family, Apaf-1, and the members of the Bcl-2 protein family, and neurotrophic factors. Retinal ganglion cells lend a convenient model system with which to investigate apoptosis in central neurons during development as well as after injury. In this review, we discuss the role of these molecules in the control of programmed cellular death in the retinotectal system. Transgenic animal models and expression studies have shown that caspases, Bcl-2, Bax, and possibly Bcl-X are necessary players for the control of programmed cellular death in retinal ganglion cells. Bax and caspase 3 expression in retinal ganglion cells is upregulated after injury, and inhibition of Bax or caspase 3 increases the survival of injured retinal ganglion cells. Neurotrophins can support the survival of injured retinal ganglion cells, but this effect is transient. The physiological role of neurotrophins in the development of the retinocollicular system seems more related to the topographic refinement of retinocollicular projections, a process that is mediated, at least partially, by selective elimination of retinal ganglion cells making inappropriate topographic projections.     

The morphology of the Limulus visual system

An ocellus of the horseshoe crab, Limulus polyphemus, has been serially sectioned for light and electron microscopy, its sensory cells have been indexed, and the interconnections of a third of these traced. The ocellus contains 155 retinula cells and 26 arhabdomeric cells, which are secondary sensory neurons. Of these, 55 retinula cells constitute 7 quasi-ommatidial assemblages, each innervated by at least one and a total of 9 arhabdomeric cells. When known electrotonic coupling patterns are compared with gap-junctional connections, retinula cells sensitive to visible or ultraviolet light can be tentatively identified. Retinula cell axons contribute collaterals to a synaptic plexus, in which the arhabdomeric cells apparently do not participate.     

The morphology of the Limulus visual system

Summary The lateral optic nerve of Limulus polyphemus, the horseshoe crab, contains 4 types of axons, which originate from eccentric cells, retinula cells, rudimentary eye cells, and from unidentified cells in the brain that give rise to the efferent fibers. Though small in diameter in a young animal, the eccentric cell axons in the adult grow to the same size as the rudimentary eye axons, which are originally the largest fibers in the nerve of the small Limulus. Cytoplasmic content, particularly the orderly distribution of microtubules, is identical in the three types of visual fibers. The segregation of rudimentary eye axons into a separate grouping within the optic nerve in small animals gives way to a homogeneous distribution in the adult. Interrupting the optic nerve leads to a proximal pile-up of secretory granules in a few fibers. The identity of these granules with those in the synaptoid terminations of photoreceptors establishes these fibers as efferent. The same operation leads to a conspicuous hypertrophy of subsurface cisternae within retinula cell axons.This study constitutes Publication No. 483 from the Oregon Regional Primate Research Center, supported by Grants FR00163 and EY 00392 from the National Institutes of Health and by a Bob Hope Grant-in-Aid by Fight-for-Sight, Inc., New York City.The author wishes to thank Mrs. Audrey Griffin for patient and excellent technical assistance.     

The morphology of the Limulus visual system

Summary The lateral rudimentary eye of Limulus polyphemus, the horseshoe crab, is located beneath the posterior border of the compound eye. It consists of a bipartite mass of guanophores and about 100 associated photoreceptor cells. These neurons, up to 150 in diameter, have standard attributes of arthropod retinula cells and send large, uninterrupted axons to the brain. Their cytoplasm contains conspicuous clumps of residual bodies and variable, but usually extensive, masses of glycogen and glycoprotein. Hence, these neurons are not neurosecretory in the strict sense, notwithstanding axonal transport of glycogen masses toward the brain. Efferent axons to the rudimentary eye terminate in synaptoid fashion on the axon hillock of sensory cells. Since the rudimentary eye does not transmit impulses to the brain, but is photosensitive, its function may reside in a metabolic responsiveness to long-term changes in illumination.This study constitutes publication No. 430 from the Oregon Regional Primate Research Center, supported by Grants FR00163 and EY00392 from the National Institutes of Health and by a Bop Hope Grant-in-Aid from Fight-for-Sight, Inc.The author wishes to thank Mrs. Audrey Griffin for patient and excellent technical assistance.     

The corticofugal pathways of the visual system

Cortical neurons belonging to the same topological ensemble send axons to thalamic and mesencephalic structures and also to contra and ipsilateral cortical areas. The projections are called the corticofugal system. This review addresses the organization and the functions of the efferent cortical fibers within the visual network. For example, the cortico-geniculate fibers participate in shaping the structure of the concentric receptive fields of geniculate cells. Namely, the size of the surround area depends on descending impulses from the cortex. By contrast, cortico-mesencephalic fibers have a more global influence on visual responses. Following the interruption of cortical activity all responses to visual stimuli decline; although in rodents and lagomorphs cortical inactivation does not eliminate those visual responses that are sent to the superior colliculus or pretectum directly from the retina. In each hemisphere it has been demonstrated that contra-lateral cortico-cortical fibers participate in the continuity of the two visual hemi-fields, as the interruption of the callosal impulses results in a truncated field in which the contralateral part of the receptive field is missing., overlaps the vertical meridian is missing. Finally, ipsilateral cortico-cortical fibers allow a consolidation of visual properties of cortical cells. It must be added that there are considerable differences among species in the organization of cortico-cortical relationships. However, this survey seems to indicate that all corticofugal axons are excitatory.