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PubMed1988

Evaluation of peripheral nerve conduction and central visual conduction in chronic alcoholics and in chronic alcoholics after prolonged abstention.

Classic statistical method (mean, standard deviation, variance) were used to analyze peripheral nerve conduction tests and visual evoked potentials in 13 chronic alcoholics and in 11 chronic alcoholics who had abstained for at least one year, in order to assess the repercussions of alcohol on the PNS and on the visual pathways and their reversibility. The sensory fibers were more affected than the motor fibers, and while the damage to the motor fibers was transient the damage to the sensory fibers was permanent and also significantly different, at least in the early stages, in the two lower limbs. Our results showed constant involvement, without clinical symptoms, of the visual potential, especially of the earliest component N70 and of the amplitude of the response. This would suggest greater involvement of the peripheral visual nervous structures, that is retino-geniculo-cortical, than of the more properly cortical structures, though these are also affected. For the visual damage too withdrawal of alcohol seems to determine a regression, though only partial, of the neurophysiological changes. The simultaneous involvement of VEP and peripheral nerve function is at variance with the assertion that optic nerve damage is a very rare event in alcoholism.

Adult↗
PubMed1980

Giant axonal neuropathy: visual and oculomotor deficits.

Giant axonal neuropathy, a generalised disorder or neurofilaments, presents as a chronic, progressive peripheral neuropathy in childhood. Evidence for central nervous system involvement is demonstrated in this study of four male patients with giant axonal neuropathy who had defective visual function and abnormal ocular motility. The visual system was studied by electroretinography, which showed normal retinal function, and by visual evoked potentials, which showed disease of both optic nerves and retrochiasmal visual pathways. The ocular motility disorder, studied by electrooculography, comprised defective pursuit, inability to maintain eccentric gaze with gaze paretic and rebound nystagmus, abnormal optokinetic responses and failure of suppression of the vestibulo-ocular reflex by fixation. These findings suggested involvement by giant axonal neuropathy of the cerebellar and brain stem pathways important in the control of ocular motility.

Axons↗
PubMed1984

The development of the retinogeniculate pathways in normal and albino ferrets.

The retinogeniculate pathways of normal and albino ferrets have been studied with horseradish peroxidase and tritiated proline used as axonal markers. The uncrossed retinogeniculate projection of adult albino ferrets is abnormally small and occupies only a fraction of the geniculate area normally occupied by uncrossed afferents. The crossed pathway is correspondingly expanded, occupying almost the entire nucleus. The geniculate laminae in the albino ferret are abnormal, showing abnormal fusions between layers receiving crossed input and abnormal discontinuities next to the small cell islands receiving uncrossed afferents. In early development, retinofugal fibres can be labelled within the optic tracts on the 28th intrauterine day and a few crossed fibres can be traced into the lateral geniculate nucleus. At this stage, the uncrossed component is extremely small in normal and albino animals and cannot be traced beyond the tract. By day 32 retinal fibres are invading the lateral geniculate nucleus bilaterally, the invasion by the crossed component being significantly more advanced than that by the uncrossed component. The uncrossed pathway of the albinos is already abnormal in terms of its size, in terms of the position it occupies in the optic tract, and in terms of its limited invasion of the lateral geniculate nucleus. The abnormally reduced size of the uncrossed component appears earlier than the abnormal segregation of the retinogeniculate terminals, suggesting that the primary action of the albino gene upon central visual pathways is prechiasmatic. At postnatal stages (41 days after conception and older) the normal, gradual withdrawal of the uncrossed fibres from the monocular segment, and the separation of crossed from uncrossed retinogeniculate terminal arbors is significantly delayed in the albinos. The uncrossed retinogeniculate terminals are abnormally sparse initially and become distributed in an abnormal, interrupted pattern as development proceeds. The abnormal pattern of geniculate lamination appears to be secondary to the abnormal distribution of retinogeniculate afferents.

Albinism↗
PubMed1981

Postnatal development of the monkey's visual system.

The sudden increase of nervous activity after birth may influence the development of many parts of the brain. The visual system provides a particularly striking example of the crucial significance of birth itself in the maturation of the nervous system, for visual experience is obviously unlikely in utero. The role of the activity of afferent neurons in maintaining, even guiding, the formation of functional connections in the visual pathways has been extensively studied in a variety of species: such work in primates might give insight into the same process in man and into the aetiology of certain developmental disorders of vision. We have performed anatomical and physiological experiments on the monkey's lateral geniculate nucleus (LGN), which receives input from the optic nerves, and the primary visual cortex, to which the LGN sends its axons. In both structures there are enormous functional changes after birth, but those in the LGN seem not to depend on normal visual stimulation while those in the cortex seem crucially dependent on visual input.

Animals↗
PubMed2004

No evidence of a lower visual field specialization for visuomotor control.

The lower visual field (loVF) has been hypothesized to demonstrate specialization for skilled, visually guided action. According to Danckert and Goodale, this visual field asymmetry indirectly suggests that the loVF has privileged connections to visuomotor networks within the dorsal visual pathway. Here we attempted to replicate the loVF advantage during the execution of a discrete aiming movement to targets of various widths (index of difficulty ranging from 1.5 to 5 bits). In addition, we employed trials in which vision of the target object was available or unavailable during the reaching movement to determine whether or not the purported visual field asymmetry reflects enhanced central planning (i.e., feedforward) or online control (i.e., feedback) processes. Reaching trajectories were examined for indicators of online amendments, and movement times and endpoint characteristics were examined to quantify possible visual field asymmetries in relative speed/accuracy trade-offs. In terms of reaching kinematics, it was found that vision of the target during the reaching movement resulted in greater online control of the reaching trajectory; however, no significant main effects or interactions involving visual field were observed. In other words, fixating in the upper or the lower region of peripersonal space did not influence the nature of reaching control (i.e., feedback vs. feedforward). Most importantly, our movement time and endpoint accuracy data elicited a robust speed/accuracy trade-off in both upper and lower regions of working space. Thus, and contrary to previous findings (such as those reported by Danckert and Goodale), the indices of difficulty coupled with the discrete aiming task used here did not elicit a lower visual field advantage for visually guided action.

Adult↗
PubMed2004

Characterizing function-structure relationships in the human visual system with functional MRI and diffusion tensor imaging.

A key objective in neuroscience is to improve our understanding of the relationship between brain function and structure. We investigated this in the posterior visual pathways of healthy volunteers by applying functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) with tractography. The optic radiations were segmented using the Probabilistic Index of Connectivity (PICo) tractography algorithm and extracted at several thresholds of connection confidence. The mean fractional anisotropy (FA) of the estimated tracts was found to correlate significantly with fMRI measures of visual cortex activity (induced by a photic stimulation paradigm). The results support the hypothesis that the visual cortical fMRI response is constrained by the external anatomical connections of the subserving optic radiations.

Adult↗
PubMed2005

Functional imaging reveals rapid development of visual response properties in the zebrafish tectum.

The visual pathway from the retina to the optic tectum in fish and frogs has long been studied as a model for neural circuit formation. Although morphological aspects, such as axonal and dendritic arborization, have been well characterized, less is known about how this translates into functional properties of tectal neurons during development. We developed a system to provide controlled visual stimuli to larval zebrafish, while performing two-photon imaging of tectal neurons loaded with a fluorescent calcium indicator, allowing us to determine visual response properties in intact fish. In relatively mature larvae, we describe receptive field sizes, visual topography, and direction and size selectivity. We also characterize the onset and development of visual responses, beginning when retinal axons first arborize in the tectum. Surprisingly, most of these properties are established soon after dendrite growth and synaptogenesis begin and do not require patterned visual experience or a protracted period of refinement.

Animals↗
PubMed1995

Electrophysiological exploration of visual function in mitochondrial diseases.

In a group of 10 children (ranging from 5 months to 15 years old) affected by diseases with mitochondrial dysfunction, 4 suffered from mitochondrial myopathy, 4 from mitochondrial encephalopathy and 2 from Friedreich's ataxia. The clinically detectable visual impairment consisted of 3 grey ocular fundi (the other 7 were normal) associated, in 2 subjects, with a mild nystagmus. Electrophysiological assessment, consisting of ERGs and flash VEPs, was systematically performed. The normal ERGs in all subjects confirmed the normal functioning of retinal electrogenesis. In contrast, the VEPs of 6 out of 10 subjects were modified: in 2 of the 4 subjects with mitochondrial myopathy, the VEPs had a hyperamplitude; in the 2 subjects with Friedreich's ataxia, the implicit time of the principal VEP peaks was increased, together with a hyperamplitude in 1 case; lastly, in 2 of the 4 subjects with mitochondrial encephalopathy, the VEPs were altered. These modifications reflected visual pathway conduction disorders with no clinical expression. Various underlying pathophysiological mechanisms possibly responsible for these modifications are discussed.

Adolescent↗
PubMed1990

Haloperidol delays visually evoked cortical potentials but not electroretinograms in mice.

Visually evoked cortical potentials (VECPs) and electroretinograms (ERG) to flash stimulation were studied in one ICR strain mouse and 23 ICR mice, respectively. The effect of a dopamine receptor blocker, haloperidol, on both responses was investigated. Significant peak latency prolongation was found in VECPs following injection of haloperidol, while the amplitude reduction of the b-wave was found in ERG. No effect of anesthetics only on ERG was found. It has been assumed that haloperidol affects VECPs related function mainly the higher visual pathway. However, the slight decrease of the b-wave amplitude of ERG could not exclude the possibility of the toxic effect on the retina.

Animals↗
PubMed2006

Enhancement of vision by monocular deprivation in adult mice.

Plasticity of vision mediated through binocular interactions has been reported in mammals only during a "critical" period in juvenile life, wherein monocular deprivation (MD) causes an enduring loss of visual acuity (amblyopia) selectively through the deprived eye. Here, we report a different form of interocular plasticity of vision in adult mice in which MD leads to an enhancement of the optokinetic response (OKR) selectively through the nondeprived eye. Over 5 d of MD, the spatial frequency sensitivity of the OKR increased gradually, reaching a plateau of approximately 36% above pre-deprivation baseline. Eye opening initiated a gradual decline, but sensitivity was maintained above pre-deprivation baseline for 5-6 d. Enhanced function was restricted to the monocular visual field, notwithstanding the dependence of the plasticity on binocular interactions. Activity in visual cortex ipsilateral to the deprived eye was necessary for the characteristic induction of the enhancement, and activity in visual cortex contralateral to the deprived eye was necessary for its maintenance after MD. The plasticity also displayed distinct learning-like properties: Active testing experience was required to attain maximal enhancement and for enhancement to persist after MD, and the duration of enhanced sensitivity after MD was extended by increasing the length of MD, and by repeating MD. These data show that the adult mouse visual system maintains a form of experience-dependent plasticity in which the visual cortex can modulate the normal function of subcortical visual pathways.

Animals↗
PubMed1991

Differential effects of unilateral optic tract transections and visual cortical lesions upon a pattern discrimination in albino rats with removal of one eye at birth.

Previously we have demonstrated that adult rats with one eye removed at birth (OEB) relearn a black-white discrimination faster than control rats monocularly enucleated at maturity (OET), when relearning is conducted after lesions of the visual cortex contralateral to the remaining eye. This faster relearning phenomenon is considered to be one behavioral expression of the functioning of the expanded uncrossed visual pathways resulting from monocular at birth. The present study was concerned with the question of whether the same phenomenon can be observed in the discrimination between alternating black and white stripes oriented horizontally and vertically. Two experiments were carried out. In the first experiment, which is a replication of one of our previous studies, relearning was conducted after the visual cortical lesions contralateral to the remaining eye. The results were consistent with those of the previous one in which neither OEBs nor OETs were found able to relearn the discrimination. In the second experiment, relearning was conducted after transections of the optic tract contralateral to the remaining eye. It was shown that under this condition both OEBs and OETs could relearn the discrimination, and furthermore, that OEBs restored the habit faster than OETs. Possible mechanisms underlying the difference in the results from the two experiments were discussed.

Animals↗
PubMed1993

Visual system of a naturally microphthalmic mammal: the blind mole rat, Spalax ehrenbergi.

Retinal projections and visual thalamo-cortical connections were studied in the subterranean mole rat, belonging to the superspecies Spalax ehrenbergi, by anterograde and retrograde tracing techniques. Quantitative image analysis was used to estimate the relative density and distribution of retinal input to different primary visual nuclei. The visual system of Spalax presents a mosaic of both regressive and progressive morphological features. Following intraocular injections of horseradish peroxidase conjugates, the retina was found to project bilaterally to all visual structures described as receiving retinal afferents in non-fossorial rodents. Structures involved in form analysis and visually guided behaviors are reduced in size by more than 90%, receive a sparse retinal innervation, and are cytoarchitecturally poorly differentiated. The dorsal lateral geniculate nucleus, as defined by cyto- and myelo-architecture, cytochrome oxidase, and acetylcholinesterase distribution as well as by afferent and efferent connections, consists of a narrow sheet 3-5 neurons thick, in the dorsal thalamus. Connections with visual cortex are topographically organized but multiple cortical injections result in widespread and overlapping distributions of geniculate neurons, thus indicating that the cortical map of visual space is imprecise. The superficial layers of the superior colliculus are collapsed to a single layer, and the diffuse ipsilateral distribution of retinal afferents also suggests a lack of precise retinotopic relations. In the pretectum, both the olivary pretectal nucleus and the nucleus of the optic tract could be identified as receiving ipsilateral and contralateral retinal projections. The ventral lateral geniculate nucleus is also bilaterally innervated, but distinct subdivisions of this nucleus or the intergeniculate leaflet could not be distinguished. The retina sends a sparse projection to the dorsal and lateral terminal nuclei of the accessory optic system. The medial terminal nucleus is not present. In contrast to the above, structures of the "non-image forming" visual pathway involved in photoperiodic perception are well developed in Spalax. The suprachiasmatic nucleus receives a bilateral projection from the retina and the absolute size, cytoarchitecture, density, and distribution of retinal afferents in Spalax are comparable with those of other rodents. A relatively hypertrophied retinal projection is observed in the bed nucleus of the stria terminalis. Other regions which receive sparse visual input include the lateral and anterior hypothalamic areas, the retrochiasmatic region, the sub-paraventricular zone, the paraventricular hypothalamic nucleus, the anteroventral and anterodorsal nuclei, the lateral habenula, the mediodorsal nucleus, and the basal telencephalon.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed2004

Chromatic and spatial properties of parvocellular cells in the lateral geniculate nucleus of the marmoset (Callithrix jacchus).

The parvocellular (PC) division of the afferent visual pathway is considered to carry neuronal signals which underlie the red-green dimension of colour vision as well as high-resolution spatial vision. In order to understand the origin of these signals, and the way in which they are combined, the responses of PC cells in dichromatic ('red-green colour-blind') and trichromatic marmosets were compared. Visual stimuli included coloured and achromatic gratings, and spatially uniform red and green lights presented at varying temporal phases and frequencies.The sensitivity of PC cells to red-green chromatic modulation was found to depend primarily on the spectral separation between the medium- and long-wavelength-sensitive cone pigments (20 or 7 nm) in the two trichromatic marmoset phenotypes studied. The temporal frequency dependence of chromatic sensitivity was consistent with centre-surround interactions. Some evidence for chromatic selectivity was seen in peripheral PC cells. The receptive field dimensions of parvocellular cells were similar in dichromatic and trichromatic animals, but the achromatic contrast sensitivity of cells was slightly higher (by about 30%) in dichromats than in trichromats. These data support the hypothesis that the primary role of the PC is to transmit high-acuity spatial signals, with red-green opponent signals appearing as an additional response dimension in trichromatic animals.

Algorithms↗
PubMed2001

Visual dysfunction between migraine events.

PURPOSE: To evaluate interictal visual dysfunction in persons with migraine in terms of spatiotemporal selectivity and location within the visual pathways. METHODS: The vision of a group of 15 persons who had experienced migraine with aura was compared with that of 15 normal age-matched control subjects. A range of thresholds was measured to evaluate precortical (background modulation, contrast thresholds for static, and moving stimuli), area V1 (orientation discrimination and motion discrimination thresholds), and higher order (global dot motion thresholds) visual processes. Testing was performed centrally and at 10 degrees in the superior visual field. For each of the tests, the spatial and temporal parameters of the stimuli were selected to bias detection toward either parvocellular or magnocellular visual mechanisms. RESULTS: No defects were found for parvocellular processes. Significant (P: < 0.05) losses were apparent with the temporal background modulation method (16 Hz), orientation discrimination (0.5 cyc/deg), and global dot motion tasks. CONCLUSIONS: Both cortical and precortical visual dysfunction were identified in migraine group 7 days after the headache. This loss was selective for targets with temporal modulation of approximately 16 Hz.

Adult↗
PubMed2005

Enhanced extrastriate visual response to bandpass spatial frequency filtered fearful faces: time course and topographic evoked-potentials mapping.

We compared electrical brain responses to fearful vs. neutral facial expressions in healthy volunteers while they performed an orthogonal gender decision task. Face stimuli either had a broadband spatial-frequency content, or were filtered to create either low spatial-frequency (LSF) or high spatial-frequency (HSF) faces, always overlapped with their complementary SF content in upside-down orientation to preserve the total stimulus energy. We tested the hypothesis that the coarse LSF content of faces might be responsible for an early modulation of event-related potentials (ERPs) to fearful expressions. Consistent with previous findings, we show that broadband images of fearful faces, relative to neutral faces, elicit a higher global field power of approximately 130 ms poststimulus onset, corresponding to an increased P1 component over lateral occipital electrodes, with neural sources located within the extrastriate visual cortex. Bandpass filtering of faces strongly affected the latency and amplitude of ERPs, with a suppression of the normal N170 response for both LSF and HSF faces, irrespective of expression. Critically, we found that LSF information from fearful faces, unlike HSF information, produced a right-lateralized enhancement of the lateral occipital P1, without any change in the scalp topography, relative to unfiltered (broadband) fearful faces. These results demonstrate that an early P1 response to fear expression depends on a visual pathway preferentially tuned to coarse-magnocellular inputs, and can persist unchanged even when the N170 generators are disrupted by SF filtering.

Adult↗
PubMed1987

The use of rhodamine-B-isothiocyanate (RITC) as an anterograde and retrograde tracer in the adult rat visual system.

We have used the fluorescent dye Rhodamine-B-Isothiocyanate (RITC) as an anterograde and retrograde marker of retinal neurons in the adult rat. Introduced into the vitreous body, RITC is taken up by retinal ganglion cells and transported anterogradely along their axons. It labels the axons and their terminal arborizations. The dye stains axonal projections for at least 30 days without detectable extracellular leakage or transneuronal passage. Furthermore, the soma and dendrites of retinal ganglion cells can also be labeled retrogradely for at least 30 days when RITC is instilled into the superior colliculus. We conclude that RITC, used previously in studies of chick embryo visual pathways, is also suitable for similar neuroanatomical investigations in the adult rat.

Animals↗
PubMed2001

Responding to feature or location: a re-examination of inhibition of return and facilitation of return.

It was found [Vision Res. 36 (1996) 2125] that reaction times for repeated targets were longer in detection and location discrimination tasks (inhibition of return; IOR) and shorter in color and orientation discrimination tasks (facilitation of return; FOR). The present experiment, using a more detailed analysis, shows that both IOR and FOR can be found in the discrimination tasks. Overall, the results are inconsistent with the notion that IOR and FOR effects reside in separate visual pathways. Rather, the results are accounted for by repetition priming and IOR that occur with specific combinations of target features and task demands.

Analysis of Variance↗
PubMed1991

Selective alterations in glutamate receptor subtypes after unilateral orbital enucleation.

Glutamate is the major excitatory neurotransmitter in the rat visual system. Using quantitative autoradiography the effect of unilateral orbital enucleation on [3H]kainate, [3H]alpha-amino-3-hydroxy-5-methyl- isoxazole-4-propionic acid [( 3H]AMPA) and [3H]glutamate binding to kainate, quisqualate and NMDA receptors respectively has been examined within anatomical components of the visual pathway at 4 time points up to 20 days post-lesion. The time course for the degeneration of retinal projection fibres was assessed in a separate group of animals by quantifying [3H]cyclohexyladenosine [( 3H]CHA) binding to presynaptic adenosine A1 receptors. Over the first 5 days after orbital enucleation, there were no significant alterations in glutamate or adenosine A1 receptor binding in visual structures of the visually deprived hemisphere. However, at 10 days post-lesion [3H]AMPA binding was significantly reduced (30%) in the visually deprived superior colliculus but unaltered in other visual structures. At this time point there was also a significant reduction (50%) in [3H]CHA binding in the visually deprived superior colliculus but not in other retino-recipient nuclei. There were similar changes in [3H]AMPA and [3H]CHA binding at 20 days post-enucleation. [3H]Kainate binding was significantly increased in the visually deprived superior colliculus only at 20 days post-enucleation. Saturation analysis of [3H]kainate and [3H]AMPA binding at this time point indicated a selective increase in the Bmax value for the high affinity [3H]kainate binding site and a concomitant decrease in the Bmax value for the high affinity [3H]AMPA binding site in the visually deprived superior colliculus. There were, however, no significant alterations in [3H]AMPA or [3H]kainate binding in other primary projection areas or in secondary visual areas (e.g. visual cortex) at any time point. NMDA sensitive [3H]glutamate binding was unaltered in the visually deprived hemisphere up to 20 days post-enucleation. These results suggest an upregulation of kainate receptors in the visually deprived superior colliculus after orbital enucleation and a loss of presynaptic quisqualate receptors on degenerating retinal fibres. The plastic alterations in kainate receptors in the superior colliculus are supportive of electrophysiological data suggesting a physiological role for these sites in mediating excitatory postsynaptic potentials in tectal neurons.

Animals↗