scholarly journals Functional Dynamics of Deafferented Early Visual Cortex in Glaucoma

2021 ◽  
Vol 15 ◽  
Author(s):  
Gokulraj T. Prabhakaran ◽  
Khaldoon O. Al-Nosairy ◽  
Claus Tempelmann ◽  
Markus Wagner ◽  
Hagen Thieme ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Retinitis Pigmentosa ◽  
Visual Stimulation ◽  
Visual Field Defects ◽  
Passive Viewing ◽  
Early Visual Cortex ◽  
Advanced Glaucoma ◽  
Projection Zone ◽  
Age Range

In advanced retinitis pigmentosa with retinal lesions, the lesion projection zone (LPZ) in the early visual cortex can be driven during visual tasks, while it remains unresponsive during passive viewing. We tested whether this finding translates to advanced glaucoma, a major cause of acquired blindness. During visual stimulation, 3T fMRI scans were acquired for participants with advanced glaucoma (n = 4; age range: 51–72) and compared to two reference groups, i.e., advanced retinitis pigmentosa (n = 3; age range: 46–78) and age-matched healthy controls with simulated defects (n = 7). The participants viewed grating patterns drifting in 8 directions (12 s) alternating with uniform gray (12 s), either during passive viewing (PV), i.e., central fixation, or during a one-back task (OBT), i.e., reports of succeeding identical motion directions. As another reference, a fixation-dot task condition was included. Only in glaucoma and retinitis pigmentosa but not in controls, fMRI-responses in the lesion projection zone (LPZ) of V1 shifted from negative for PV to positive for OBT (p = 0.024 and p = 0.012, respectively). In glaucoma, these effects also reached significance in V3 (p = 0.006), while in V2 there was a non-significant trend (p = 0.069). The general absence of positive responses in the LPZ during PV underscores the lack of early visual cortex bottom-up plasticity for acquired visual field defects in humans. Trends in our exploratory analysis suggesting the task-dependent LPZ responses to be inversely related to visual field loss, indicate the benefit of patient stratification strategies in future studies with greater sample sizes. We conclude that top-down mechanisms associated with task-elicited demands rather than visual cortex remapping appear to shape LPZ responses not only in retinitis pigmentosa, but also in glaucoma. These insights are of critical importance for the development of schemes for treatment and rehabilitation in glaucoma and beyond.

scholarly journals Functional MRI of visual cortex predicts training-induced recovery in stroke patients with homonymous visual field defects

2020 ◽  
Author(s):  
J.A. Elshout ◽  
D.P. Bergsma ◽  
A.V. van den Berg ◽  
Koen Haak
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Visual Stimulation ◽  
Daily Life ◽  
Visual Field Defects ◽  
Wide Field ◽  
Stroke Patients ◽  
Daily Life Activities ◽  
Humphrey Perimetry ◽  
Field Defects

Post-chiasmatic damage to the visual system leads to homonymous visual field defects (HVDs), which can severely interfere with daily life activities. Visual Restitution Training (VRT) can recover parts of the affected visual field in patients with chronic HVDs, but training outcome is variable. An untested hypothesis suggests that training potential may be largest in regions with ‘neural reserve’, where cortical responses to visual stimulation do not lead to visual awareness as assessed by Humphrey perimetry—a standard behavioural visual field test. Here, we tested this hypothesis in a sample of twenty-seven hemianopic stroke patients, who participated in an assiduous 80-hour VRT program. For each patient, we collected Humphrey perimetry and wide-field fMRI-based retinotopic mapping data prior to training. In addition, we used Goal Attainment Scaling to assess whether personal activities in daily living improved. After training, we assessed with a second Humphrey perimetry measurement whether the visual field was improved and evaluated which personal goals were attained. Confirming the hypothesis, we found significantly larger improvements of visual sensitivity at field locations with neural reserve. These visual field improvements implicated both regions in primary visual cortex and higher order visual areas. In addition, improvement in daily life activities correlated with the extent of visual field enlargement but not sensitivity gain. Our findings are an important step toward understanding the mechanisms of visual restitution as well as predicting training efficacy in stroke patients with chronic hemianopia.

scholarly journals Neural Correlates of Sustained Spatial Attention in Human Early Visual Cortex

2007 ◽  
Vol 97 (1) ◽  
pp. 229-237 ◽  
Author(s):  
Michael A. Silver ◽  
David Ress ◽  
David J. Heeger
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Visual Stimulation ◽  
Human Subjects ◽  
Delay Period ◽  
Cortical Areas ◽  
Time Period ◽  
Variable Duration ◽  
Early Visual Cortex ◽  
Perceptual Performance

Attention is thought to enhance perceptual performance at attended locations through top-down attention signals that modulate activity in visual cortex. Here, we show that activity in early visual cortex is sustained during maintenance of attention in the absence of visual stimulation. We used functional magnetic resonance imaging (fMRI) to measure activity in visual cortex while human subjects performed a visual detection task in which a variable-duration delay period preceded target presentation. Portions of cortical areas V1, V2, and V3 representing the attended part of the visual field exhibited sustained increases in activity throughout the delay period. Portions of these cortical areas representing peripheral, unattended parts of the visual field displayed sustained decreases in activity. The data were well fit by a model that assumed the sustained neural activity was constant in amplitude over a time period equal to that of the actual delay period for each trial. These results demonstrate that sustained attention responses are present in early visual cortex (including primary visual cortex), in the absence of a visual stimulus, and that these responses correlate with the allocation of visuospatial attention in both the spatial and temporal domains.

scholarly journals Chromatic Pupilloperimetry Measures Correlate With Visual Acuity and Visual Field Defects in Retinitis Pigmentosa Patients

2020 ◽  
Vol 9 (8) ◽  
pp. 10
Author(s):  
Ifat Sher ◽  
Yisroel Tucker ◽  
Maya Gurevich ◽  
Amit Hamburg ◽  
Ettel Bubis ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Visual Field ◽  
Retinitis Pigmentosa ◽  
Visual Field Defects ◽  
Field Defects

scholarly journals A machine-learning algorithm correctly classifies cortical evoked potentials from both natural retinal stimulation and electrical stimulation of the optic nerve

2021 ◽  
Author(s):  
Vivien Gaillet ◽  
Elodie Geneviève Zollinger ◽  
Diego Ghezzi
Keyword(s):  
Electrical Stimulation ◽  
Visual Cortex ◽  
Optic Nerve ◽  
Visual Field ◽  
Primary Visual Cortex ◽  
Nerve Stimulation ◽  
Visual Stimulation ◽  
Cortical Activity ◽  
Artificial Vision ◽  
Optic Nerve Stimulation

AbstractObjectiveOptic nerve’s intraneural stimulation is an emerging neuroprosthetic approach to provide artificial vision to totally blind patients. An open question is the possibility to evoke individual non-overlapping phosphenes via selective intraneural optic nerve stimulation. To begin answering this question, first, we aim at showing in preclinical experiments with animals that each intraneural electrode could evoke a distinguishable activity pattern in the primary visual cortex.ApproachWe performed both patterned visual stimulation and patterned electrical stimulation in healthy rabbits while recording evoked cortical activity with an electrocorticogram array in the primary visual cortex. Electrical stimulation was delivered to the optic nerve with the intraneural array OpticSELINE. We used a support vector machine algorithm paired to a linear regression model to classify cortical responses originating from visual stimuli located in different portions of the visual field and electrical stimuli from the different electrodes of the OpticSELINE.Main resultsCortical activity induced by visual and electrical stimulation could be classified with nearly 100% accuracy relative to the specific location in the visual field or electrode in the array from which it originated. For visual stimulation, the accuracy increased with the separation of the stimuli and reached 100% for separation higher than 7 degrees. For electrical stimulation, at low current amplitudes, the accuracy increased with the distance between electrodes, while at higher current amplitudes, the accuracy was nearly 100% already for the shortest separation.SignificanceOptic nerve’s intraneural stimulation with the OpticSELINE induced discernible cortical activity patterns. These results represent a leap forward for intraneural optic nerve stimulation towards artificial vision.

scholarly journals Population Dynamics of Early Visual Cortex during Working Memory

2018 ◽  
Vol 30 (2) ◽  
pp. 219-233 ◽  
Author(s):  
Masih Rahmati ◽  
Golbarg T. Saber ◽  
Clayton E. Curtis
Keyword(s):  
Working Memory ◽  
Population Dynamics ◽  
Visual Cortex ◽  
Parietal Cortex ◽  
Visual Stimulus ◽  
Visual Stimulation ◽  
Brain Activity ◽  
Top Down ◽  
Population Activity ◽  
Early Visual Cortex

Although the content of working memory (WM) can be decoded from the spatial patterns of brain activity in early visual cortex, how populations encode WM representations remains unclear. Here, we address this limitation by using a model-based approach that reconstructs the feature encoded by population activity measured with fMRI. Using this approach, we could successfully reconstruct the locations of memory-guided saccade goals based on the pattern of activity in visual cortex during a memory delay. We could reconstruct the saccade goal even when we dissociated the visual stimulus from the saccade goal using a memory-guided antisaccade procedure. By comparing the spatiotemporal population dynamics, we find that the representations in visual cortex are stable but can also evolve from a representation of a remembered visual stimulus to a prospective goal. Moreover, because the representation of the antisaccade goal cannot be the result of bottom–up visual stimulation, it must be evoked by top–down signals presumably originating from frontal and/or parietal cortex. Indeed, we find that trial-by-trial fluctuations in delay period activity in frontal and parietal cortex correlate with the precision with which our model reconstructed the maintained saccade goal based on the pattern of activity in visual cortex. Therefore, the population dynamics in visual cortex encode WM representations, and these representations can be sculpted by top–down signals from frontal and parietal cortex.

Visual fMRI Responses in Human Superior Colliculus Show a Temporal–Nasal Asymmetry That Is Absent in Lateral Geniculate and Visual Cortex

2007 ◽  
Vol 97 (2) ◽  
pp. 1495-1502 ◽  
Author(s):  
Richard Sylvester ◽  
Oliver Josephs ◽  
Jon Driver ◽  
Geraint Rees
Keyword(s):  
Visual Cortex ◽  
Superior Colliculus ◽  
High Spatial Resolution ◽  
Visual Stimulation ◽  
Field Stimulation ◽  
Physiological Measures ◽  
Cortical Areas ◽  
Lateral Geniculate ◽  
Early Visual Cortex ◽  
Contralateral Eye

Eye patching has revealed enhanced saccadic latencies or attention effects when orienting toward visual stimuli presented in the temporal versus nasal hemifields of humans. Such behavioral advantages have been tentatively proposed to reflect possible temporal–nasal differences in the retinotectal pathway to the superior colliculus, rather than in the retinogeniculate pathway or visual cortex. However, this has not been directly tested with physiological measures in humans. Here, we examined responses of the human superior colliculus (SC) to contralateral visual field stimulation, using high spatial resolution fMRI, while manipulating which hemifield was stimulated and orthogonally which eye was patched. The SC responded more strongly to visual stimulation when eye-patching made this stimulation temporal rather than nasal. In contrast, the lateral geniculate nucleus (LGN) plus retinotopic cortical areas V1–V3 did not show any temporal–nasal differences and differed from the SC in this respect. These results provide the first direct physiological demonstration in humans that SC shows temporal–nasal differences that LGN and early visual cortex apparently do not. This may represent a temporal hemifield bias in the strength of the retinotectal pathway, leading to a preference for the contralateral hemifield in the contralateral eye.

scholarly journals Typical visual-field locations enhance processing in object-selective channels of human occipital cortex

2018 ◽  
Vol 120 (2) ◽  
pp. 848-853 ◽  
Author(s):  
Daniel Kaiser ◽  
Radoslaw M. Cichy
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Functional Mri ◽  
Object Perception ◽  
Occipital Cortex ◽  
Natural Environments ◽  
Lower Visual Field ◽  
Cortical Processing ◽  
Upper Visual Field ◽  
Early Visual Cortex

Natural environments consist of multiple objects, many of which repeatedly occupy similar locations within a scene. For example, hats are seen on people’s heads, while shoes are most often seen close to the ground. Such positional regularities bias the distribution of objects across the visual field: hats are more often encountered in the upper visual field, while shoes are more often encountered in the lower visual field. Here we tested the hypothesis that typical visual field locations of objects facilitate cortical processing. We recorded functional MRI while participants viewed images of objects that were associated with upper or lower visual field locations. Using multivariate classification, we show that object information can be more successfully decoded from response patterns in object-selective lateral occipital cortex (LO) when the objects are presented in their typical location (e.g., shoe in the lower visual field) than when they are presented in an atypical location (e.g., shoe in the upper visual field). In a functional connectivity analysis, we relate this benefit to increased coupling between LO and early visual cortex, suggesting that typical object positioning facilitates information propagation across the visual hierarchy. Together these results suggest that object representations in occipital visual cortex are tuned to the structure of natural environments. This tuning may support object perception in spatially structured environments. NEW & NOTEWORTHY In the real world, objects appear in predictable spatial locations. Hats, commonly appearing on people’s heads, often fall into the upper visual field. Shoes, mostly appearing on people’s feet, often fall into the lower visual field. Here we used functional MRI to demonstrate that such regularities facilitate cortical processing: Objects encountered in their typical locations are coded more efficiently, which may allow us to effortlessly recognize objects in natural environments.

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