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Cortex; a Journal Devoted To the Study... Jan 2018The division of labor in visual processing between two anatomically relatively separate cortical pathways, a ventral and a dorsal stream, has been hotly debated in the... (Review)
Review
The division of labor in visual processing between two anatomically relatively separate cortical pathways, a ventral and a dorsal stream, has been hotly debated in the last decades. One influential model is the What & How pathway model, suggesting that the separation is along ventral perception versus dorsal action, although the degree of functional separation between the two streams is controversial. An implication of this model is that perception and memory-guided movements are highly sensitive to visual contextual illusions, whereas visually-guided movements are largely immune to them. Here, we summarize our recent behavioral and imaging data obtained in single and double saccade paradigms that test this proposal, with a focus on the role of time in visuomotor processing and updating. We describe results showing that presentation time of the illusion affects both saccade amplitude and perceptual judgments in a similar way. We also discuss behavioral findings showing that visuomotor updating is affected by illusory context. Complementary neuroimaging data suggest a neural correlate of these findings in dorsal stream areas. Taken together, these results are suggestive of a dynamic, common visual representation that drives both perception and action, or - at least - that there is no absolute functional specialization of the two visual processing streams.
Topics: Factor VIII; Functional Neuroimaging; Magnetic Resonance Imaging; Psychomotor Performance; Saccades; Visual Pathways; Visual Perception
PubMed: 28024879
DOI: 10.1016/j.cortex.2016.11.013 -
Journal of Clinical Neuroscience :... Jun 2016In this paper we review the visual snow (VS) characteristics of a case cohort of 32 patients. History of symptoms and associated co-morbidities, ophthalmic examination,...
In this paper we review the visual snow (VS) characteristics of a case cohort of 32 patients. History of symptoms and associated co-morbidities, ophthalmic examination, previous investigations and the results of intuitive colourimetry were collected and reviewed. VS symptoms follow a stereotypical description and are strongly associated with palinopsia, migraine and tinnitus, but also tremor. The condition is a chronic one and often results in misdiagnosis with psychiatric disorders or malingering. Colour filters, particularly in the yellow-blue colour spectrum, subjectively reduced symptoms of VS. There is neurobiological evidence for the syndrome of VS that links it with other disorders of visual and sensory processing such as migraine and tinnitus. Colour filters in the blue-yellow spectrum may alter the koniocellular pathway processing, which has a regulatory effect on background electroencephalographic rhythms, and may add weight to the hypothesis that VS is a thalamocortical dysrhythmia of the visual pathway.
Topics: Adolescent; Adult; Cerebral Cortex; Color Vision; Diagnosis, Differential; Female; Humans; Male; Middle Aged; Migraine Disorders; Syndrome; Thalamus; Tinnitus; Tremor; Vision Disorders; Visual Pathways
PubMed: 26791474
DOI: 10.1016/j.jocn.2015.12.001 -
NeuroImage. Clinical 2024Impaired motion perception in schizophrenia has been associated with deficits in social-cognitive processes and with reduced activation of visual sensory regions,...
Impaired motion perception in schizophrenia has been associated with deficits in social-cognitive processes and with reduced activation of visual sensory regions, including the middle temporal area (MT+) and posterior superior temporal sulcus (pSTS). These findings are consistent with the recent proposal of the existence of a specific 'third visual pathway' specialized for social perception in which motion is a fundamental component. The third visual pathway transmits visual information from early sensory visual processing areas to the STS, with MT+ acting as a critical intermediary. We used functional magnetic resonance imaging to investigate functioning of this pathway during processing of naturalistic videos with explicit (real) motion and static images with implied motion cues. These measures were related to face emotion recognition and motion-perception, as measured behaviorally. Participants were 28 individuals with schizophrenia (Sz) and 20 neurotypical controls. Compared to controls, individuals with Sz showed reduced activation of third visual pathway regions (MT+, pSTS) in response to both real- and implied-motion stimuli. Dysfunction of early visual cortex and pulvinar were also associated with aberrant real-motion processing. Implied-motion stimuli additionally engaged a wide network of brain areas including parietal, motor and frontal nodes of the human mirror neuron system. The findings support concepts of MT+ as a mediator between visual sensory areas and higher-order brain and argue for greater focus on MT+ contributions to social-cognitive processing, in addition to its well-documented role in visual motion processing.
Topics: Humans; Schizophrenia; Visual Pathways; Temporal Lobe; Brain; Magnetic Resonance Imaging; Brain Mapping; Motion Perception; Photic Stimulation
PubMed: 38309185
DOI: 10.1016/j.nicl.2024.103570 -
PLoS Biology Aug 2023Understanding the dynamics of stability/plasticity balances during adulthood is pivotal for learning, disease, and recovery from injury. However, the brain-wide...
Understanding the dynamics of stability/plasticity balances during adulthood is pivotal for learning, disease, and recovery from injury. However, the brain-wide topography of sensory remapping remains unknown. Here, using a first-of-its-kind setup for delivering patterned visual stimuli in a rodent magnetic resonance imaging (MRI) scanner, coupled with biologically inspired computational models, we noninvasively mapped brain-wide properties-receptive fields (RFs) and spatial frequency (SF) tuning curves-that were insofar only available from invasive electrophysiology or optical imaging. We then tracked the RF dynamics in the chronic visual deprivation model (VDM) of plasticity and found that light exposure progressively promoted a large-scale topographic remapping in adult rats. Upon light exposure, the initially unspecialized visual pathway progressively evidenced sharpened RFs (smaller and more spatially selective) and enhanced SF tuning curves. Our findings reveal that visual experience following VDM reshapes both structure and function of the visual system and shifts the stability/plasticity balance in adults.
Topics: Rats; Animals; Visual Pathways; Brain; Learning; Optical Imaging
PubMed: 37590177
DOI: 10.1371/journal.pbio.3002229 -
Current Biology : CB Jul 2023Cephalopods are highly visual animals with camera-type eyes, large brains, and a rich repertoire of visually guided behaviors. However, the cephalopod brain evolved...
Cephalopods are highly visual animals with camera-type eyes, large brains, and a rich repertoire of visually guided behaviors. However, the cephalopod brain evolved independently from those of other highly visual species, such as vertebrates; therefore, the neural circuits that process sensory information are profoundly different. It is largely unknown how their powerful but unique visual system functions, as there have been no direct neural measurements of visual responses in the cephalopod brain. In this study, we used two-photon calcium imaging to record visually evoked responses in the primary visual processing center of the octopus central brain, the optic lobe, to determine how basic features of the visual scene are represented and organized. We found spatially localized receptive fields for light (ON) and dark (OFF) stimuli, which were retinotopically organized across the optic lobe, demonstrating a hallmark of visual system organization shared across many species. An examination of these responses revealed transformations of the visual representation across the layers of the optic lobe, including the emergence of the OFF pathway and increased size selectivity. We also identified asymmetries in the spatial processing of ON and OFF stimuli, which suggest unique circuit mechanisms for form processing that may have evolved to suit the specific demands of processing an underwater visual scene. This study provides insight into the neural processing and functional organization of the octopus visual system, highlighting both shared and unique aspects, and lays a foundation for future studies of the neural circuits that mediate visual processing and behavior in cephalopods.
Topics: Animals; Octopodiformes; Eye; Visual Perception; Nervous System; Visual Pathways
PubMed: 37343556
DOI: 10.1016/j.cub.2023.05.069 -
Journal of the Neurological Sciences Aug 2022Visual field loss is associated with poor post-stroke functional outcomes. However, early detection of visual field loss is often challenging in patients with disabling...
Visual field loss is associated with poor post-stroke functional outcomes. However, early detection of visual field loss is often challenging in patients with disabling stroke. This study explored the association between the microstructural integrity of the retrogeniculate pathway and visual field loss in disabling stroke patients undergoing inpatient rehabilitation. Thirty patients with stroke lesions involving the retrogeniculate visual pathway were included. The degree of visual field loss was determined by the visual field index and mean deviation using automated perimetry. The fractional anisotropy (FA) values were obtained for the lateral geniculate nucleus and optic radiation; the FA laterality indices, representing the degree of degeneration, were calculated. The FA values were compared between the affected and unaffected hemispheres. The patients were categorized into complete and incomplete hemianopia groups, and their FA values were compared. The relationship between the FA laterality index and the degree of visual field loss was assessed. FA values of the lateral geniculate nucleus and optic radiation were lower on the affected side than on the unaffected side (P < 0.001 and P < 0.001, respectively). The affected optic radiation in the complete hemianopia group showed a lower FA value than in the incomplete group (P = 0.006). The FA laterality index of the optic radiation was positively correlated with the degree of visual field loss (visual field index, ρ = 0.629; mean deviation, ρ = 0.568). The quantification of the retrogeniculate visual pathway may aid in detecting post-stroke visual field loss. The microstructural integrity of the optic radiation is associated with the severity of visual field loss.
Topics: Anisotropy; Diffusion Tensor Imaging; Hemianopsia; Humans; Stroke; Vision Disorders; Visual Field Tests; Visual Fields; Visual Pathways
PubMed: 35640329
DOI: 10.1016/j.jns.2022.120297 -
PLoS Computational Biology Apr 2023Flies detect and track moving targets among visual clutter, and this process mainly relies on visual motion. Visual motion is analyzed or computed with the pathway from...
Flies detect and track moving targets among visual clutter, and this process mainly relies on visual motion. Visual motion is analyzed or computed with the pathway from the retina to T4/T5 cells. The computation of local directional motion was formulated as an elementary movement detector (EMD) model more than half a century ago. Solving target detection or figure-ground discrimination problems can be equivalent to extracting boundaries between a target and the background based on the motion discontinuities in the output of a retinotopic array of EMDs. Individual EMDs cannot measure true velocities, however, due to their sensitivity to pattern properties such as luminance contrast and spatial frequency content. It remains unclear how local directional motion signals are further integrated to enable figure-ground discrimination. Here, we present a computational model inspired by fly motion vision. Simulations suggest that the heavily fluctuating output of an EMD array is naturally surmounted by a lobula network, which is hypothesized to be downstream of the local motion detectors and have parallel pathways with distinct directional selectivity. The lobula network carries out a spatiotemporal smoothing operation for visual motion, especially across time, enabling the segmentation of moving figures from the background. The model qualitatively reproduces experimental observations in the visually evoked response characteristics of one type of lobula columnar (LC) cell. The model is further shown to be robust to natural scene variability. Our results suggest that the lobula is involved in local motion-based target detection.
Topics: Animals; Motion Perception; Diptera; Vision, Ocular; Retina; Visual Pathways
PubMed: 37083880
DOI: 10.1371/journal.pcbi.1011077 -
Acta Ophthalmologica Mar 2016Many eye diseases reduce visual acuity or are associated with visual field defects. Because of the well-defined retinotopic organization of the connections of the visual... (Review)
Review
Many eye diseases reduce visual acuity or are associated with visual field defects. Because of the well-defined retinotopic organization of the connections of the visual pathways, this may affect specific parts of the visual pathways and cortex, as a result of either deprivation or transsynaptic degeneration. For this reason, over the past several years, numerous structural magnetic resonance imaging (MRI) studies have examined the association of eye diseases with pathway and brain changes. Here, we review structural MRI studies performed in human patients with the eye diseases albinism, amblyopia, hereditary retinal dystrophies, age-related macular degeneration (AMD) and glaucoma. We focus on two main questions. First, what have these studies revealed? Second, what is the potential clinical relevance of their findings? We find that all the aforementioned eye diseases are indeed associated with structural changes in the visual pathways and brain. As such changes have been described in very different eye diseases, in our view the most parsimonious explanation is that these are caused by the loss of visual input and the subsequent deprivation of the visual pathways and brain regions, rather than by transsynaptic degeneration. Moreover, and of clinical relevance, for some of the diseases - in particular glaucoma and AMD - present results are compatible with the view that the eye disease is part of a more general neurological or neurodegenerative disorder that also affects the brain. Finally, establishing structural changes of the visual pathways has been relevant in the context of new therapeutic strategies to restore retinal function: it implies that restoring retinal function may not suffice to also effectively restore vision. Future structural MRI studies can contribute to (i) further establish relationships between ocular and neurological neurodegenerative disorders, (ii) investigate whether brain degeneration in eye diseases is reversible, (iii) evaluate the use of neuroprotective medication in ocular disease, (iv) determine optimal timing for retinal implant insertion and (v) establish structural MRI examination as a diagnostic tool in ophthalmology.
Topics: Brain Diseases; Eye Diseases; Humans; Magnetic Resonance Imaging; Vision Disorders; Visual Acuity; Visual Cortex; Visual Fields; Visual Pathways
PubMed: 26361248
DOI: 10.1111/aos.12825 -
Fa Yi Xue Za Zhi Aug 2023To investigate the characteristics and objective assessment method of visual field defects caused by optic chiasm and its posterior visual pathway injury.
OBJECTIVES
To investigate the characteristics and objective assessment method of visual field defects caused by optic chiasm and its posterior visual pathway injury.
METHODS
Typical cases of visual field defects caused by injuries to the optic chiasm, optic tracts, optic radiations, and visual cortex were selected. Visual field examinations, visual evoked potential (VEP) and multifocal visual evolved potential (mfVEP) measurements, craniocerebral CT/MRI, and retinal optical coherence tomography (OCT) were performed, respectively, and the aforementioned visual electrophysiological and neuroimaging indicators were analyzed comprehensively.
RESULTS
The electrophysiological manifestations of visual field defects caused by optic chiasm injuries were bitemporal hemianopsia mfVEP abnormalities. The visual field defects caused by optic tract, optic radiation, and visual cortex injuries were all manifested homonymous hemianopsia mfVEP abnormalities contralateral to the lesion. Mild relative afferent pupil disorder (RAPD) and characteristic optic nerve atrophy were observed in hemianopsia patients with optic tract injuries, but not in patients with optic radiation or visual cortex injuries. Neuroimaging could provide morphological evidence of damages to the optic chiasm and its posterior visual pathway.
CONCLUSIONS
Visual field defects caused by optic chiasm, optic tract, optic radiation, and visual cortex injuries have their respective characteristics. The combined application of mfVEP and static visual field measurements, in combination with neuroimaging, can maximize the assessment of the location and degree of visual pathway damage, providing an effective scheme for the identification of such injuries.
Topics: Humans; Optic Chiasm; Visual Pathways; Visual Fields; Evoked Potentials, Visual; Random Amplified Polymorphic DNA Technique; Hemianopsia; Vision Disorders; Optic Nerve Injuries; Brain Injuries, Traumatic
PubMed: 37859473
DOI: 10.12116/j.issn.1004-5619.2023.230309 -
Neuroscience Bulletin Sep 2020
Topics: Animals; Humans; Vision, Binocular; Visual Cortex; Visual Pathways
PubMed: 32367252
DOI: 10.1007/s12264-020-00506-6