Objective: To report the frequency of neuro-ophthalmologic cases seen over one working week by a senior neuro-ophthalmologist in Singapore and to determine a pattern in the incidence of neuro-ophthalmic diseases. Methods: A retrospective review of 57 consecutive neuro-ophthalmologic cases seen by one senior neuro-ophthalmologist from June 14 to 18, 2010 was done. All patients underwent a complete neuro-ophthalmologic examination. Demographic data and clinical diagnoses were gathered. Results: A total of 57 patients were seen. Thirty-one percent (18) of these patients were new consultations while the remaining 61% (39) were follow-up visits. Fifty-two percent were females (30) with a mean age of 53 years while 47% were males (27) with a mean age of 49 years. Nineteen cases involved disorders of the optic nerve followed by disorders of ocular motility (11), optic chiasm, visual pathways, and/or visual cortex (14). Among the cases involving the optic nerve, 5 were ischemic optic neuropathy. In respect to disorders of ocular motility, ocular myasthenia gravis (n=5) was the most common condition seen. Pituitary adenomas comprised the bulk of the disorders of the optic chiasm (4). The remaining neuro-ophthalmic cases were almost evenly distributed. A very rare case of Froin’s syndrome was also seen. Conclusion Overall, during the five-day neuro-ophthalmologic clinic, majority of cases were ischemic in nature, reminding readers that systemic diseases, such as hypertension, diabetes mellitus, hyperlipidemia, commonly manifest in the eye. Hence, better systemic control of these diseases is necessary.
Optic Nerve Diseases ; Visual Pathways ; Visual Cortex

No abstract available.
Animals ; Cats* ; Neurons* ; Visual Cortex*

The amplitude and latency of visual evoked potentials to pattern-reversal half-field stimulation were measured in 20 normal right-handed subjects to determine whether the individual contribution of right and left cerebral hemispheres is different as related to the generation of pattern-evoked potentials. The amplitude and latency of P1 from a lateral occipital electrode ipsilateral to the halffield stimulation were significantly greater with right half-field wtimulation. The amplitude and latency difference between both sides probably reflects asymmetries of human striate cortex.
Cerebrum ; Electrodes ; Evoked Potentials, Visual* ; Humans ; Visual Cortex

The core of visual processing is the identification and recognition of the objects relevant to cognitive behaviors. In natural environment, visual input is often comprised of highly complex 3-dimensional signals involving multiple visual objects. One critical determinant of object recognition is visual contour. Despite substantial insights on visual contour processing gained from previous findings, these studies have focused on limited aspects or particular stages of contour processing. So far, a systematic perspective of contour processing that comprehensively incorporates previous evidence is still missing. We therefore propose an integrated framework of the cognitive and neural mechanisms of contour processing, which involves three mutually interacting cognitive stages: contour detection, border ownership assignment and contour integration. For each stage, we provide an elaborated discussion of the neural properties, processing mechanism, and its functional interaction with the other stages by summarizing the relevant electrophysiological and human cognitive neuroscience evidence. Finally, we present the major challenges for further unraveling the mechanisms of visual contour processing.
Cognition ; Form Perception ; Humans ; Visual Cortex ; physiology ; Visual Perception

Studies have shown that spatial attention remarkably affects the trial-to-trial response variability shared between neurons. Difficulty in the attentional task adjusts how much concentration we maintain on what is currently important and what is filtered as irrelevant sensory information. However, how task difficulty mediates the interactions between neurons with separated receptive fields (RFs) that are attended to or attended away is still not clear. We examined spike count correlations between single-unit activities recorded simultaneously in the primary visual cortex (V1) while monkeys performed a spatial attention task with two levels of difficulty. Moreover, the RFs of the two neurons recorded were non-overlapping to allow us to study fluctuations in the correlated responses between competing visual inputs when the focus of attention was allocated to the RF of one neuron. While increasing difficulty in the spatial attention task, spike count correlations were either decreased to become negative between neuronal pairs, implying competition among them, with one neuron (or none) exhibiting attentional enhancement of firing rate, or increased to become positive, suggesting inter-neuronal cooperation, with one of the pair showing attentional suppression of spiking responses. Besides, the modulation of spike count correlations by task difficulty was independent of the attended locations. These findings provide evidence that task difficulty affects the functional interactions between different neuronal pools in V1 when selective attention resolves the spatial competition.
Animals ; Attention/physiology* ; Macaca mulatta ; Neurons/physiology* ; Photic Stimulation ; Primary Visual Cortex ; Visual Cortex/physiology*

PURPOSE: Most of recent MR imagings of cerebral cortex activation have been performed by using high field magnet above 2-T or echo-planar imaging technique. We report our experience on imaging of cerebral cortex activation with a widely available standard 1.5-T MR. MATERIALS AND METHODS: Series of gradient-echo images (TR/TE/flip angle :80/60/40 degrees64 x 128 matrix) were acquired alternatively during the periods of rest and task in five normal volunteers. Finger movement (n=10 ;5 right, 5 left) and flashing photic stimulation (n=l) were used as a motor task and a visual task to activate the motor cortex and visual cortex, respectively. Activation images were obtained by subtracting sum of rest images from that of task images. Changes of signal intensity were analyzed over the periods of rest and task. RESULTS: Activation images were obtained in all cases. Changes of signal intensity between rest and task periods were 6.5-14.6%(mean, 10.5%) in the motor cortex and 4.2% in the visual cortex. CONCLUSION: Functional imaging of cerebral cortex activation could be performed with a widely available 1.5-T MR. Widespread applications of this technique to basic and clinical neuroscience are expected.
Cerebral Cortex* ; Echo-Planar Imaging ; Fingers ; Healthy Volunteers ; Motor Cortex ; Neurosciences ; Photic Stimulation ; Visual Cortex

This study was aimed to clarify the change of neuropeptide Y -immunoreactive (NPY -IR) and NADPH -diaphorase (NADPH -d)-positive neurons associated with aging of ICR and C57Bl/6 mice. To verify the effect of aging on NPY and NADPH -d neurons in the cerebral cortex, the tissues were stained by the immunohistochemical and histochemical method. The coexistence of NADPH -d and NPY was found in the cerebral cortex of the ICR and C57Bl/6 mice. The 30 -week -old ICR mice showed a significant increase in the number of NPY - IR neurons in comparison with the 5 -week -old mice in primary motor, secondary somatosensory, ectorhinal, auditory and visual cortex. In the 30 -week -old C57Bl/6 mice, the number of NPY -IR neurons was significantly increased in primary and secondary somatosensory cortex, decreased in retrosplenial and visual cortex compared to the 5 -week -old group. However, the number of NPY -IR/NADPH -d positive neurons of ICR mice was no significant changes in most cerebral cortical areas except insular and perirhinal cortex in the 30 week -old group in comparison with 5 -week -old group of both mice group. The number of coexisted neurons of 30 -week -old C57Bl/6 mice was significantly decreased in primary motor and auditory cortex compared to the 5 -week - old group. These results provides the morphological evidence for the change of NPY -IR neurons that do not contain NADPH -d may be more susceptible to age -related change than NADPH -d -containing neurons in the cerebral cortex of mice.
Aging ; Animals ; Auditory Cortex ; Cerebral Cortex* ; Mice* ; Mice, Inbred ICR ; NADP ; Neurons* ; Neuropeptide Y ; Neuropeptides* ; Somatosensory Cortex ; Visual Cortex

Efficient coding theory proposes that sensory systems in the brain have been adapted to process natural scenes efficiently over the long history of evolution. Computational modeling the statistical regularities of natural images is therefore beneficial to our understanding of the mechanisms of visual information processing. In this paper, we briefly review the recent progress in using efficient coding approaches to study the encoding of natural images in the visual system.
Animals ; Evoked Potentials, Visual ; physiology ; Humans ; Models, Statistical ; Photic Stimulation ; Visual Cortex ; physiology ; Visual Perception ; physiology

The human visual system efficiently extracts local elements from cluttered backgrounds and integrates these elements into meaningful contour perception. This process is a critical step before object recognition, in which contours often play an important role in defining the shapes and borders of the to-be-recognized objects. However, the neural mechanism of the contour integration is still under debate. The investigation of the neural mechanism underlying contour integration could deepen our understanding of perceptual grouping in the human visual system and advance the development of the algorithms for image grouping and segmentation in computer vision. Here, we review two theoretical frameworks that were proposed over the past decades. The first framework is based on hardwired horizontal connection in primary visual cortex, while the second one emphasizes the role of recurrent connections within intra- and inter-areas. At the end of review, we also raise the unsolved issues that need to be addressed in future studies.
Form Perception ; Humans ; Models, Neurological ; Pattern Recognition, Visual ; Visual Cortex ; physiology ; Visual Perception

How the brain perceives objects and classifies perceived objects is one of the important goals of visual cognitive neuroscience. Previous research has shown that when we see objects, the brain's ventral visual pathway recognizes and classifies them, leading to different ways of interacting with them. In this paper, we summarize the latest research progress of the ventral visual pathway related to the visual classification of objects. From the perspective of the neural representation of objects and its underlying mechanisms in the visual cortex, we summarize the current research status of the two important organizational dimensions of object animacy and real-world size, provide new insights, and point out the direction of further research.
Brain Mapping/methods* ; Magnetic Resonance Imaging ; Pattern Recognition, Visual ; Photic Stimulation ; Visual Cortex ; Visual Pathways