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PubMed1999

[Electrophysiological findings in patients with SCA6].

The major symptom of spinocerebellar ataxia type 6 (SCA6) is progressive cerebellar ataxia. MRI revealed isolated cerebellar atrophy without brainstem and cerebral involvement. Up to the present electrophysiological abnormalities in patients with SCA6 have not been intensively investigated. We performed electrophysiological examination, such as multi-modality evoked potentials, in 10 patients with SCA6. We analyzed the electrophysiological data including the results previously reported. When compared with SCA1, 2 and MJD, specific findings in electrophysiological studies are obscure in SCA6. Existence of subclinical lesions in peripheral nerves, pyramidal tract, auditory pathway, visual pathway, and sensory pathway was suggested in some cases with SCA6. It is important to consider the effect of age, because age at onset is relatively late in SCA6.

Age of Onset↗
PubMed2005

[Bibliometrical analysis of Medline publications in neuro-ophthalmology].

PURPOSE: To analyze the contents of international publications in neuro-ophthalmology during the past decade. METHODS: Medline was searched with the Internet provider PubMed in December 2003, using "eye disease" as the medical subject heading and "optic nerve", "visual pathway", "visual cortex", "ocular motility", and "pupil" as subhead terms for retrieving English-language neuro-ophthalmic articles that were published between 1993 and 2002. RESULTS: A total of 9,585 English-written original articles available for analysis were concerned with a wide range of basic and clinical neuro-ophthalmic subjects, the order of frequency being ocular motility (22.8%), optic nerve (17.2%), visual functions (17.2%), visual cortex (10.1%), retina (8.6%), ocular adnexa (5.9%), optic chiasm (5.8%), brainstem (3.1%), and pupil (3.0%). The major optic nerve disorders included demyelinated optic neuritis, Leber hereditary optic neuropathy, and ischemic optic neuropathy. The major ocular motility disorders were supranuclear palsy, progressive external ophthalmoplegia, and ocular motor nerve disease. The articles were contributed from 73 countries. The top 10 countries ranked by share were USA (40.4%), United Kingdom (10.2%), Japan (8.7 %), Germany (6.0%), Italy (4.0%), Canada (3.5%), France (3.5%), Australia (2.2%), Israel (1.8%), and Turkey (1.8%). Researchers with diverse specialties contributed to the neuro-ophthalmic publications, including ophthalmology (40.5%), neurology/neuroscience (21.7%), and neurosurgery (5.9%). CONCLUSIONS: Neuro-ophthalmic papers were interdisciplinary, contributed by researchers with diverse specialties, and published in a wide range of biomedical as well as neurological journals.

Bibliometrics↗
PubMed1997

How reliably does a neuron in the visual motion pathway of the fly encode behaviourally relevant information?

How reliably neurons convey information depends on the extent to which their activity is affected by stochastic processes which are omnipresent in the nervous system. The functional consequences of neuronal noise can only be assessed if the latter is related to the response components that are induced in a normal behavioural situation. In the present study the reliability of neural coding was investigated for an identified neuron in the pathway processing visual motion information of the fly (Lucilia cuprina). The stimuli used to investigate the neuronal performance were not exclusively defined by the experimenter. Instead, they were generated by the fly itself, i.e. by its own actions and reactions in a behavioural closed-loop experiment, and subsequently replayed to the animal while the activity of an identified motion-sensitive neuron was recorded. Although the time course of the neuronal responses is time-locked to the stimulus, individual response traces differ slightly from each other due to stochastic fluctuations in the timing and number of action potentials. Individual responses thus consist of a stimulus-induced and a stochastic response component. The stimulus-induced response component can be recovered most reliably from noisy neuronal signals if these are smoothed by intermediate-sized time windows (40-100 ms). At this time scale the best compromise is achieved between smoothing out the noise and maintaining the temporal resolution of the stimulus-induced response component. Consequently, in the visual motion pathway of the fly, behaviourally relevant motion stimuli can be resolved best at a time scale where the timing of individual spikes does not matter.

Animals↗
PubMed2004

Electrophysiological correlates of associative visual agnosia lesioned in the ventral pathway.

Visual agnosia has been well studied by anatomical, neuropsychological and neuroimaging studies. However, functional changes in the brain have been rarely assessed by electrophysiological methods. We carried out electrophysiological examinations on a 23-year-old man with associative visual agnosia, prosopagnosia and cerebral achromatopsia to evaluate the higher brain dysfunctions of visual recognition. Electrophysiological methods consisted of achromatic, chromatic and category-specific visual evoked potentials (CS-VEPs), and event-related potentials (ERPs) with color and motion discrimination tasks. Brain magnetic resonance imaging revealed large white matter lesions in the bilateral temporo-occipital lobes involving the lingual and fusiform gyri (V4) and inferior longitudinal fasciculi due to multiple sclerosis. Examinations including CS-VEPs demonstrated dysfunctions of face and object perception while sparing semantic word perception after primary visual cortex (V1) in the ventral pathway. ERPs showed abnormal color perception in the ventral pathway with normal motion perception in the dorsal pathway. These electrophysiological findings were consistent with lesions in the ventral pathway that were detected by clinical and neuroimaging findings. Therefore, CS-VEPs and ERPs with color and motion discrimination tasks are useful methods for assessing the functional changes of visual recognition such as visual agnosia.

Adult↗
PubMed2002

Visual experience before eye-opening and the development of the retinogeniculate pathway.

Visual experience before eye-opening is not usually thought to have any developmental significance. Here we show that naturalistic visual stimuli presented through unopened eyelids robustly activate neurons in the ferret dorsal lateral geniculate nucleus. Further, dark-rearing prior to natural eye-opening has striking effects upon geniculate physiology. Receptive field maps after dark-rearing show increased convergence of On- and Off-center responses, and neurons frequently respond to both bright and dark phases of drifting gratings. There is also increased selectivity for the orientation of the gratings. These abnormalities of On-Off segregation can be explained by the finding that the responses of immature On and Off cells to naturalistic stimuli are strongly anticorrelated.

Action Potentials↗
PubMed2004

Differential impact of parvocellular and magnocellular pathways on visual impairment in apperceptive agnosia?

The term "visual form agnosia" describes a disorder characterized by problems recognizing objects, poor copying,and distinguishing between simple geometric shapes despite normal intellectual abilities. Visual agnosia has been interpreted as a disorder of the magnocellular visual system, caused by an inability to separate figure from ground by sampling information from extended regions of space and to integrate it with fine-grain local information. However,this interpretation has hardly been tested with neuropsychological or functional brain imaging methods, mainly because the magnocellular and parvocellular structures are highly interconnected in the visual system. We studied a patient (AM) who had suffered a sudden heart arrest, causing hypoxic brain damage. He was/is severely agnosic, as apparent in both the Birmingham Object Recognition Battery and the Visual Object and Space Battery. First- and especially second-order motion perception was also impaired, but AM experienced no problems in grasping and navigating through space. The patient revealed a normal P100 in visual evoked potentials both with colored and fine-grained achromatic checkerboards. But the amplitude of the P100 was clearly decreased if a coarse achromatic checkerboard was presented.The physiological and neuropsychological findings indicate that AM experienced problems integrating information over extended regions of space and in detecting second-order motion. This may be interpreted as a disorder of the magnocellular system, with intact parvocellular system and therefore preserved ability to detect both local features and colors.

Agnosia↗
PubMed2003

Brain stem pursuit pathways: dissociating visual, vestibular, and proprioceptive inputs during combined eye-head gaze tracking.

Eye-head (EH) neurons within the medial vestibular nuclei are thought to be the primary input to the extraocular motoneurons during smooth pursuit: they receive direct projections from the cerebellar flocculus/ventral paraflocculus, and in turn, project to the abducens motor nucleus. Here, we recorded from EH neurons during head-restrained smooth pursuit and head-unrestrained combined eye-head pursuit (gaze pursuit). During head-restrained smooth pursuit of sinusoidal and step-ramp target motion, each neuron's response was well described by a simple model that included resting discharge (bias), eye position, and velocity terms. Moreover, eye acceleration, as well as eye position, velocity, and acceleration error (error = target movement - eye movement) signals played no role in shaping neuronal discharges. During head-unrestrained gaze pursuit, EH neuron responses reflected the summation of their head-movement sensitivity during passive whole-body rotation in the dark and gaze-movement sensitivity during smooth pursuit. Indeed, EH neuron responses were well predicted by their head- and gaze-movement sensitivity during these two paradigms across conditions (e.g., combined eye-head gaze pursuit, smooth pursuit, whole-body rotation in the dark, whole-body rotation while viewing a target moving with the head (i.e., cancellation), and passive rotation of the head-on-body). Thus our results imply that vestibular inputs, but not the activation of neck proprioceptors, influence EH neuron responses during head-on-body movements. This latter proposal was confirmed by demonstrating a complete absence of modulation in the same neurons during passive rotation of the monkey's body beneath its neck. Taken together our results show that during gaze pursuit EH neurons carry vestibular- as well as gaze-related information to extraocular motoneurons. We propose that this vestibular-related modulation is offset by inputs from other premotor inputs, and that the responses of vestibuloocular reflex interneurons (i.e., position-vestibular-pause neurons) are consistent with such a proposal.

Action Potentials↗
PubMed1983

Visually guided behaviour of cats in the absence of retino-geniculo-cortical pathways.

Visually guided behaviour was studied in cats after various lesions of the central nervous system in order to obtain further information about the functional capacity and developmental plasticity of subcortical visual areas. Hemidecortications were made in all cats either within 5 days of birth (neonatal) or more than one year after birth (adult). In addition the optic chiasm was transected at another time in some cats, or the optic tract contralateral to the hemidecortication in the other cats. Visual behaviour was investigated with several tests: Locomotion among obstacles (free field). Search for openings of chambers (labyrinth). Jumping from/between boxes of different heights (jumpbox). Object vision and visual field (fish-picking cage). Visual learning (T-maze). Pupillary light reactions. Visual placing reactions. Reactions to moving visual stimuli. The hemidecortications caused different visual defects for the adults and the neonatals, which in addition showed varying prominence depending on type of test. All cats showed defects which were caused by hemianopia. Less defects were found in the free field, labyrinth and jumpbox tests for the neonatals compared to the adults. The difference is attributed to a better ability of the neonatals to utilize subcortical visual areas for visual orientation in space. The subsequent optic chiasm or optic tract sections permitted comparison between the functional capacity of crossed and uncrossed retinal fibres to subcortical structures. The uncrossed fibres were found to be unable to maintain any visually guided behaviour even for the above described neonatals. It appears likely that the better vision of the neonatally hemidecorticated cats was mediated via crossed retinal fibres to subcortical structures. It was eventually possible to demonstrate visually guided behaviour which was mediated via subcortical structures also in the adult hemidecorticated cats in the T-maze. The residual vision consisted of an ability to discriminate contrast differences. The present findings emphasize the potential functional importance of subcortical visual areas in the cat, especially after early brain damage. The differential findings from the different tests have shown the limitations of single test investigations. The presence of learnt visual behaviour in the absence of spontaneous visual behaviour for individual animals of this study advocates for greater use of spontanous behaviour for investigations of visual defects caused by brain lesions.

Animals↗
PubMed1988

Parallel pathways can conduct visual CS information during classical conditioning of the NM response.

Single and combined lesions were made to the lateral geniculate nucleus (LGN), the superficial layers of the superior colliculus (SC), and the pretectal nuclei (Ptc) prior to conditioning of the nictitating membrane (NM) response in rabbit with a visual conditioned stimulus (CS). Due to technical considerations, lesions of the dorsal LGN were accompanied by lesions of the visual cortex, the only output of the dorsal LGN, in order to render the dorsal LGN nonfunctional. Single lesions to any one of the 3 target systems (LGN, SC, Ptc) did not alter the rate of conditioning. Furthermore, double lesions to any 2 of the systems did not prevent conditioning, although LGN + SC lesions significantly retarded acquisition. When all 3 systems were lesioned, however, animals never acquired to the visual CS, although they successfully conditioned to an auditory CS. The results indicate that in rabbit there are parallel visual pathways individually capable of supporting the acquisition of conditioned NM responses.

Animals↗
PubMed1990

Visual association pathways in human brain.

Visual information processing are realized by the posterior association cortex spreading in front of the striate and parastriate areas from which two major visual association pathways arise. The dorsal or the occipito-parietal pathway which transmits the inputs from the peripheral as well as the central visual field to the parietal association cortex is responsible for the visuospatial analysis of the visual informations. The occipito-temporal or the ventral pathway originates only from the foveal vision area, and sends the visual inputs to the inferior temporal lobe which engages in visual pattern or whole gestalt recognition of the visual informations. In addition to this dichotomous disposition of the dorsal and the ventral visual association pathways in each cerebral hemisphere, there is another type of functional specialization which is hierarchical rather than dichotomous. In the left cerebral hemisphere, the collateral pathways arise from both dorsal and ventral main streams and engage in the process of reading, or the verbal mode of visual information processing.

Agnosia↗
PubMed1982

Rehabilitation following brain damage: some neurophysiological mechanisms. Functional recovery in the visual and vestibular pathways.

The visual and labyrinthine sensing systems are often neglected in the rehabilitation process of patients with central nervous system (CNS) lesions. Nevertheless, their integrity is essential for the construction of motor tasks ranging from accurate reaching to the co-ordinated behaviours of posture and locomotion. This tasks may be influenced considerably by the roles of the visual and vestibular systems in the perceptual analysis of localizing objects in space ("egocentric localization") and of spatial orientation of the body ("ego-orientation") and in controlling oculomotor and postural stability. The anatomy, physiology, clinical relevance and patterns of recovery of function of two specific visual-vestibular related behaviours is addressed, namely ocular stability and egocentric localization. Emphasis is placed upon such issues as (a) motor learning in complete and incomplete lesions as adjudged from observations of peripheral vestibular nerve disorders; (b) the role of the cerebellum in calibrating motor performance with particular reference to the modifiability of the vestibulo-ocular reflex to attain ocular stability; (c) the use of redundant or complementary structures as assumed from evidence of recovery from chronic visual field deficits; and (d) specified behavioural tactics as a mechanism for adaptation.

Central Nervous System Diseases↗
PubMed2000

GAL4/UAS-WGA system as a powerful tool for tracing Drosophila transsynaptic neural pathways.

Visualization of specific transsynaptic neural pathways is an indispensable technique for understanding the relationship between structure and function in the nervous system. Here, we demonstrate the application of the wheat germ agglutinin (WGA) transgene technique for tracing transsynaptic neural pathways in Drosophila. The intracellular localization of WGA was examined by immunoelectron microscopy. WGA signals were detected in granule-like structures in both the outer photoreceptor cells expressing WGA and the second-order laminar neurons. Misexpression of tetanus toxin (TNT), which inactivates N-synaptobrevin, in the outer photoreceptor cells resulted in the elimination of on/off transients in electroretinogram (ERG) recordings and in a great reduction in WGA transfer into laminar neurons, suggesting that anterograde WGA transsynaptic transfer is dependent mainly on synaptic transmission. Retrograde WGA transfer was also detected upon its forced expression in muscle cells. WGA primarily expressed in muscle cells was taken up by motoneuron axons and transported to their cell bodies in the ventral nerve cord, suggesting that WGA can trace motoneuronal pathways in combination with the muscle-specific GAL4 driver. Thus, the GAL4/UAS-WGA system should facilitate the dissection of the Drosophila neural circuit formation and/or synaptic activity in various regions and at various developmental stages.

Animals↗
PubMed1986

Role of the extra-geniculate pathway in visual guidance. I. Effects of lesioning the superior colliculus in the cat.

We investigated the effect of superior colliculus lesions on the performance of a visually guided paw movement. Six cats were trained to perform a paw movement toward a lever moving in front of them at an adjustable speed. The target was visible and accessible for approximately 700 ms, corresponding to the time needed to traverse the aperture situated in front of the animal. To receive a food pellet reward the cat had to press on the lever during this presentation period. Efficient and misguided movements were recorded, and their relative proportions calculated. For each rewarded movement, the response time (delay between the appearance of the lever in the aperture and the cat's press) was automatically computed. After stabilization of their performance, each cat underwent a bilateral electrolytic lesion of the superior colliculi. In all cases it markedly affected precision. The cats first recovered their ability to reach an immobile lever and later on their ability to point to the lever while it was moving. However, even after two months of postoperative training, two cats had still not completely recovered their preoperative precision. All lesioned animals displayed a perturbation in their response time distribution. Anterior lesions, involving area centralis projection, were more effective in producing the deficits than more posterior ones. The results are discussed in relation to the involvement of the superior colliculus in the analysis of peripheral fixed or moving stimuli.

Animals↗
PubMed1985

Dynamic topography of visual evoked potential in children: a study of the development of the visual system.

To study the development of the visual system, the dynamic topography of the visual evoked potential (VDT) was investigated in 30 normal children aged from two weeks to four years. Twenty-three of the 30 children (77%) showed reliable VDT. The results showed three steps in the development of the visual system in these young children. The first step was seen during the first 4 months after birth, and it was represented by a shortening of duration and an increasing of amplitude in N70 in the occipital region. The second step was seen between 9 months and 2 years of age, and it was represented by a shortening of duration and an increasing of amplitude in P100 and P150 over a widespread area in the occipito-parieto-temporal region. The third step was not clearly seen until 3 years of age, and was represented by the appearance of P200, the so called "vertex potential", around the occipitoparietal region. These three steps in the development of the visual system seemed to be closely related to the time-course of the development in the myelination and maturation of the neuron synapses in the visual pathway and visual cortex. With the aid of VDT, it was possible to clarify that the visual system in children develops step by step from a low level to a high level of the visual function.

Aging↗
PubMedDate not supplied

[Electrophysiologic studies of the pathways of visual afferentation in the forebrain of the dogfish Squalus acanthias].

Afferent visual projections to the pallium of the telencephalon have been investigated in immobilized conscious dogfish Squalus acanthias using electrophysiological recording the evoked potentials and neuronal reactions elicited by electric stimulation of the optic nerve. Analysis and comparison of the parameters of the components of the evoked potentials in the telencephalon and tectum opticum indicate the existence of two visual subsystems (the retino-thalamo-telencephalic and the retino-tecto-thalamo-telencephalic ones) in the dogfish.

Animals↗
PubMed1991

Dissociation of object and spatial visual processing pathways in human extrastriate cortex.

The existence and neuroanatomical locations of separate extrastriate visual pathways for object recognition and spatial localization were investigated in healthy young men. Regional cerebral blood flow was measured by positron emission tomography and bolus injections of H2(15)O, while subjects performed face matching, dot-location matching, or sensorimotor control tasks. Both visual matching tasks activated lateral occipital cortex. Face discrimination alone activated a region of occipitotemporal cortex that was anterior and inferior to the occipital area activated by both tasks. The spatial location task alone activated a region of lateral superior parietal cortex. Perisylvian and anterior temporal cortices were not activated by either task. These results demonstrate the existence of three functionally dissociable regions of human visual extrastriate cortex. The ventral and dorsal locations of the regions specialized for object recognition and spatial localization, respectively, suggest some homology between human and nonhuman primate extrastriate cortex, with displacement in human brain, possibly related to the evolution of phylogenetically newer cortical areas.

Adult↗
PubMed2005

[Study on anisometropic amblyopia by simultaneously recording multifocal VEP and multifocal ERG].

OBJECTIVE: To investigate the characteristic changes of the retina, the visual pathway and the visual cortex in patients with anisometropic amblyopia by simultaneously recording multifocal VEP and multifocal ERG. METHODS: Pattern and flash simultaneously recording of the multifocal VEP and ERG of both eyes of 24 anisometropic amblyopes were recorded and the results were compared with those of 30 normal subjects. RESULTS: In different retinal areas the amplitudes of multifocal pattern VEP and ERG and second order kernel of multifocal flash VEP and ERG of the amblyopic eyes were reduced. In amblyopic eyes the latencies of mVEP were markedly prolonged while no changes of the mERG latencies were found. Amplitudes of first order kernel of multifocal flash VEP and ERG in amblyopic eyes were reduced while no changes in latencies. The abnormalities of multifocal pattern VEP waveforms in amblyopia were larger in central area than in peripheral and were correlated with the damage of visual acuity of the amblyopic eyes. Retinocortical time of multifocal pattern and the second order kernel of multifocal flash responses were prolonged in amblyopic eyes, while no changes were found for the first order kernel responses. CONCLUSION: The mVEP and mERG results revealed characteristic suggesting a malfunction of the retina, the visual pathway and the visual cortex in amblyopic patients.

Adolescent↗
PubMed2006

Studies of human visual pathophysiology with visual evoked potentials.

Visual evoked potentials (VEPs) offer reproducible and quantitative data on the function of the visual pathways and the visual cortex. Pattern reversal VEPs to full-field stimulation are best suited to evaluate anterior visual pathways while hemi-field stimulation is most effective in the assessment of post-chiasmal function. However, visual information is processed simultaneously via multiple parallel channels and each channel constitutes a set of sequential processes. We outline the major parallel pathways of the visual system from the retina to the primary visual cortex and higher visual areas via lateral geniculate nucleus that receive visual input. There is no best method of stimulus selection, rather visual stimuli and VEPs' recording should be tailored to answer specific clinical and/or research questions. Newly developed techniques that can assess the functions of extrastriate as well as striate cortices are discussed. Finally, an algorithm of sequential steps to evaluate the various levels of visual processing is proposed and its clinical use revisited.

Brain Diseases↗