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Revista de NeurologiaMost of our impressions of the world and our memory are based on sight. Being able to look around us and recognise our surroundings involves the activity of several... (Review)
Review
INTRODUCTION
Most of our impressions of the world and our memory are based on sight. Being able to look around us and recognise our surroundings involves the activity of several processing pathways in the brain that interact with each other and integrate information until it becomes conscious. Little is known about all these mechanisms today and therefore new tools must be developed and employed to enable us to further our understanding in this field.
DEVELOPMENT
The visual system is one of the most complex sensory systems. An important part of what we do know about how it is organised derives from studies carried out in animals or from clinical findings in patients with visual problems caused by local lesions. In recent years, advances in neurophysiological recording and stimulation techniques have made it possible to study visual functioning in a far more direct manner. Transcranial magnetic stimulation (TMS) is one of these new techniques and can be used to assess the excitability of the occipital cortex, induce conscious visual perceptions, produce 'virtual lesions' and even carry out direct manipulation of several visuoperceptual tasks. In this work we present the main applications of TMS in the study of the visual pathway, its most significant technical aspects and its clinical usefulness from the diagnostic point of view and within the field of visual rehabilitation.
CONCLUSIONS
TMS is a safe technique with important clinical and therapeutic implications, which offers valuable data about the mechanisms underlying the processing of visual information, and it is therefore becoming a very useful tool within the areas of neuroscience and clinical neurology.
Topics: Humans; Phosphenes; Transcranial Magnetic Stimulation; Visual Cortex; Visual Pathways
PubMed: 18351568
DOI: No ID Found -
Current Biology : CB Dec 2015The architecture of computational devices is shaped by their energy consumption. Energetic constraints are used to design silicon-based computers but are poorly...
The architecture of computational devices is shaped by their energy consumption. Energetic constraints are used to design silicon-based computers but are poorly understood for neural computation. In the brain, most energy is used to reverse ion influxes generating excitatory postsynaptic currents (EPSCs) and action potentials. Thus, EPSCs should be small to minimize energy use, but not so small as to impair information transmission. We quantified information flow through the retinothalamic synapse in the visual pathway in brain slices, with cortical and inhibitory input to the postsynaptic cell blocked. Altering EPSC size with dynamic clamp, we found that a larger-than-normal EPSC increased information flow through the synapse. Thus, the evolutionarily selected EPSC size does not maximize retinal information flow to the cortex. By assessing the energy used on postsynaptic ion pumping and action potentials, we show that, instead, the EPSC size optimizes the ratio of retinal information transmitted to energy consumed. These data suggest maximization of information transmission per energy used as a synaptic design principle.
Topics: Energy Metabolism; Excitatory Postsynaptic Potentials; Visual Pathways
PubMed: 26671670
DOI: 10.1016/j.cub.2015.10.063 -
Progress in Neuro-psychopharmacology &... Oct 2015This review highlights morphological and functional anomalies found along the entire visual pathway in schizophrenia, from the retina to the cortex. Based on the... (Review)
Review
This review highlights morphological and functional anomalies found along the entire visual pathway in schizophrenia, from the retina to the cortex. Based on the evidence of widespread anatomical and functional visual abnormalities, we posited that a neurodevelopmental anomaly occurring early in life was likely to explain those. Incidentally, support to the neurodevelopmental theory of schizophrenia is strongly emerging from many neurobiological domains. In vertebrates, the first visual structures migrate toward the orbit position at the end of the fourth week of gestation. A neurodevelopmental defect around that time on these embryonic structures could account for the visual anomalies in schizophrenia. Retinol activity might be involved in the process. Future research in schizophrenia should focus on early visual testing, on trials combining multiple visual anomaly assessments and a closer look to retinol activity during the pregnancy.
Topics: Brain; Humans; Retina; Schizophrenia; Vision Disorders; Visual Pathways
PubMed: 25934388
DOI: 10.1016/j.pnpbp.2015.04.007 -
Journal of Magnetic Resonance Imaging :... May 2010To characterize and evaluate functional and anatomic changes of visual pathway lesions during hyperbaric oxygen (HBO) treatment with blood-oxygenation-level-dependent...
PURPOSE
To characterize and evaluate functional and anatomic changes of visual pathway lesions during hyperbaric oxygen (HBO) treatment with blood-oxygenation-level-dependent functional MRI (BOLD-fMRI) and diffusion tensor imaging (DTI).
MATERIALS AND METHODS
Sixteen patients with visual pathway lesions received HBO treatment. Both BOLD-fMRI and DTI were performed before and after the treatment, while 12 healthy subjects were also studied with 2 examinations as control. The t-tests were used for the comparison of number of activated voxels (AVs) and fractional anisotropy (FA) between the two groups, and within the patient group before and after HBO treatment. Visual acuity of the patient group before and after the treatment was compared using Wilcoxon signed-rank test.
RESULTS
Before the treatment, both AVs (P < 0.01) and FA (P < 0.05) in the bilateral cortexes of occipital lobes were significantly less in the patient group than in the control group. After the treatment, both AVs (P < 0.05) and FA (P < 0.05) were significantly increased. Moreover, The FA of 6 patients with lesions in the optical nerve was greater than the FA of the other 10 patients with lesions in the optic radiation (P < 0.05).
CONCLUSION
BOLD-fMRI combined with DTI was useful for the characterization and evaluation of anatomic and functional changes of visual pathway lesions and their development during HBO treatment.
Topics: Adolescent; Adult; Aged; Brain Injuries; Diffusion Magnetic Resonance Imaging; Female; Humans; Hyperbaric Oxygenation; Magnetic Resonance Imaging; Male; Middle Aged; Visual Cortex; Visual Pathways; Young Adult
PubMed: 20432338
DOI: 10.1002/jmri.22142 -
Clinical Neurology and Neurosurgery Sep 2021A 74-year-old man presented with complex visual hallucinations with a left inferior quadrantanopia. The characteristics of the visual hallucinations met the criteria for...
A 74-year-old man presented with complex visual hallucinations with a left inferior quadrantanopia. The characteristics of the visual hallucinations met the criteria for the Charles Bonnet syndrome. Brain magnetic resonance imaging (MRI) revealed a right occipital falx meningioma. Fusion images of gadolinium-enhanced MRI and F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) of the brain demonstrated hypometabolism in the right primary and secondary visual cortices, and an ipsilateral hypermetabolism in a focal area of the medial aspect of the secondary visual cortex as well as the lateral part of the ventral visual pathway. These findings imply that hyperactivation of the ventral visual pathway, especially the lateral aspect of the ventral occipitotemporal cortex, may be related to the face hallucinations in this patient. This case highlights features of FDG-PET that can explain the pathophysiology of the Charles Bonnet syndrome.
Topics: Aged; Brain; Charles Bonnet Syndrome; Fluorodeoxyglucose F18; Humans; Magnetic Resonance Imaging; Male; Positron-Emission Tomography; Visual Pathways
PubMed: 34329811
DOI: 10.1016/j.clineuro.2021.106832 -
Nursing Mirror Mar 1983
Topics: Brain; Humans; Retina; Visual Pathways; Visual Perception
PubMed: 6550935
DOI: No ID Found -
Journal of Cognitive Neuroscience Nov 2018Object recognition requires dynamic transformations of low-level visual inputs to complex semantic representations. Although this process depends on the ventral visual...
Object recognition requires dynamic transformations of low-level visual inputs to complex semantic representations. Although this process depends on the ventral visual pathway, we lack an incremental account from low-level inputs to semantic representations and the mechanistic details of these dynamics. Here we combine computational models of vision with semantics and test the output of the incremental model against patterns of neural oscillations recorded with magnetoencephalography in humans. Representational similarity analysis showed visual information was represented in low-frequency activity throughout the ventral visual pathway, and semantic information was represented in theta activity. Furthermore, directed connectivity showed visual information travels through feedforward connections, whereas visual information is transformed into semantic representations through feedforward and feedback activity, centered on the anterior temporal lobe. Our research highlights that the complex transformations between visual and semantic information is driven by feedforward and recurrent dynamics resulting in object-specific semantics.
Topics: Computational Biology; Female; Humans; Magnetic Resonance Imaging; Magnetoencephalography; Male; Pattern Recognition, Visual; Photic Stimulation; Random Allocation; Semantics; Theta Rhythm; Visual Pathways
PubMed: 30125217
DOI: 10.1162/jocn_a_01325 -
Journal of AAPOS : the Official... Aug 2006
Topics: Cost-Benefit Analysis; Diagnostic Techniques, Ophthalmological; Evoked Potentials, Visual; Humans; Optic Nerve Glioma; Optic Nerve Neoplasms; Treatment Outcome; Visual Pathways
PubMed: 16935225
DOI: 10.1016/j.jaapos.2006.06.002 -
Neuroreport Jun 2022Age-related macular degeneration (AMD) is the leading cause of visual loss in the developed world and damages the central retina. Growing evidences demonstrated that AMD...
Decreased spontaneous brain activity in the dorsal visual pathway in age-related macular degeneration patients revealed by fractional amplitude of low-frequency fluctuation.
BACKGROUND
Age-related macular degeneration (AMD) is the leading cause of visual loss in the developed world and damages the central retina. Growing evidences demonstrated that AMD patients were associated with brain structure changes in visual pathway. However, it remains unknown whether alterations of spontaneous brain activity changes occur in AMD patients.
PURPOSE
The purpose of this study was to investigate the effect of central vision loss on spontaneous brain activity in AMD patients.
MATERIAL AND METHODS
Seventeen AMD patients and 17 healthy controls (HCs) underwent resting-state MRI scans. The fractional amplitude of low-frequency fluctuations (fALFFs) was applied to investigate the spontaneous brain activity changes in AMD patients.
RESULTS
Compared with HC group, AMD patients showed significant decreased fALFF values in the right calcarine/cuneus (brodmann area 17,8) and right superior parietal lobule (brodmann area 7).
CONCLUSION
Our results showed that AMD patients had decreased brain activities in the dorsal visual pathway, which offer important insights into the neural mechanisms of central visual field defect in AMD patients.
Topics: Brain; Brain Mapping; Humans; Macular Degeneration; Magnetic Resonance Imaging; Vision Disorders; Visual Pathways
PubMed: 35594429
DOI: 10.1097/WNR.0000000000001797 -
Neurology Jul 1996
Topics: Albinism; Humans; Visual Pathways
PubMed: 8710117
DOI: 10.1212/wnl.47.1.311