Visual cortex activation induced by tactile stimulation in late-blind individuals with retinitis pigmentosa

Advances in Neuroscience, Not Devices, Will Determine the Effectiveness of Visual Prostheses

Background: Innovations in engineering and neuroscience have enabled the development of sophisticated visual prosthetic devices. In clinical trials, these devices have provided visual acuities as high as 20/460, enabled coarse navigation, and even allowed for reading of short words. However, long-term commercial viability arguably rests on attaining even better vision and more definitive improvements in tasks of daily living and quality of life. Purpose: Here we review technological and biological obstacles in the implementation of visual prosthetics. Conclusions: Research in the visual prosthetic field has tackled significant technical challenges, including biocompatibility, signal spread through neural tissue, and inadvertent activation of passing axons; however, significant gaps in knowledge remain in the realm of neuroscience, including the neural code of vision and visual plasticity. We assert that further optimization of prosthetic devices alone will not provide markedly improved visual outcomes without significant advances in our understanding of neuroscience.

Arterial Spin Labeling Perfusion Magnetic Resonance Imaging Reveals Resting Cerebral Blood Flow Alterations Specific to Retinitis Pigmentosa Patients

Purpose: This study aimed to assess resting cerebral blood flow (CBF) changes in retinitis pigmentosa (RP) patients using a pseudo-continuous arterial spin labeling (pCASL) perfusion method.Methods: Forty-nine RP patients and 51 healthy controls (HCs) underwent T1-weighted structural and pCASL sequence magnetic resonance imaging (MRI) scans at rest. Two-sample t-tests were performed to compare CBF differences between groups. Pearson correlation was used to analyze relationships between CBF values and clinical variables in the RP group.Results: Compared with HCs, RP patients had significantly lower CBF values in the bilateral cuneus/lingual gyrus/precuneus/posterior cingulate/middle occipital gyrus. In the RP group, CBF values in the left middle occipital and inferior occipital gyrus were positively correlated with mean retinal nerve fiber layer thickness; furthermore, CBF values in several regions were correlated with duration of disease and age of onset.Conclusions: Our results highlighted that RP patients exhibited decreased CBF values in the visual cortices and vision-related cortices. The results suggest that altered CBF might contribute to trans-synaptic retrograde degeneration of the visual pathway in RP patients.

Altered functional connectivity of primary visual cortex in late blindness

BACKGROUND

Previous studies demonstrated that early blindness is associated with abnormal intrinsic functional connectivity (FC) between the primary visual cortex (V1) and other sensory areas. However, the V1 pattern of spontaneous neural activity occurring in late blindness (LB) remains unknown. The purpose of this study was to investigate the intrinsic FC patterns of V1 in LB.

MATERIALS AND METHODS

Thirty LB individuals (18 males and 12 females; mean age: 38.76±14.43 years) and 30 sighted controls (SCs) individuals (18 males and 12 females; mean age: 38.67±13.85 years) closely matched for age, sex, and education, underwent resting-state magnetic resonance imaging scans. Region of interest analysis was performed to extract the correlation coefficient matrix among each pair of Brodmann area (BA) 17 and FC between V1 and vision-related subcortical nuclei.

RESULTS

Compared with SCs, LB individuals showed a decreased FC between the left V1 and the bilateral cuneus (CUN)/lingual gyrus (LGG)/calcarine (CAL) (BA 18/19/30) and left precentral gyrus (PreCG) and the postcentral gyrus (PostCG) (BA 2/3/4). Also, LB individuals showed a decreased FC between the right V1 and the bilateral CUN/LGG/CAL (BA 18/19/30) and the left PreCG and PostCG (BA 2/3/4/6) (voxel-level: P<0.01, cluster-level: P<0.05). Meanwhile, LB individuals showed a decreased FC between the left V1 and the right V1 and increased FC between the left V1 and the right superior colliculus, the right V1, and the left hippocampus (P<0.05). Moreover, a positive correlation was observed between the onset age of blindness and FC values in V1 to CUN/LGG/CAL in LB.

CONCLUSION

Our results highlighted that LB induces a decreased FC between V1 and higher visual areas, motor cortices, and somatosensory cortices at rest. This might indicate that LB humans could present with impaired top-down modulations, visual imagery, and vision-motor function.

Low Vision and Plasticity: Implications for Rehabilitation

Low vision is any type of visual impairment that affects activities of daily living. In the context of low vision, we define plasticity as changes in brain or perceptual behavior that follow the onset of visual impairment and that are not directly due to the underlying pathology. An important goal of low-vision research is to determine how plasticity affects visual performance of everyday activities. In this review, we consider the levels of the visual system at which plasticity occurs, the impact of age and visual experience on plasticity, and whether plastic changes are spontaneous or require explicit training. We also discuss how plasticity may affect low-vision rehabilitation. Developments in retinal imaging, noninvasive brain imaging, and eye tracking have supplemented traditional clinical and psychophysical methods for assessing how the visual system adapts to visual impairment. Findings from contemporary research are providing tools to guide people with low vision in adopting appropriate rehabilitation strategies.

Plasticity in the human visual cortex: an ophthalmology-based perspective

Neuroplasticity refers to the ability of the brain to reorganize the function and structure of its connections in response to changes in the environment. Adult human visual cortex shows several manifestations of plasticity, such as perceptual learning and adaptation, working under the top-down influence of attention. Plasticity results from the interplay of several mechanisms, including the GABAergic system, epigenetic factors, mitochondrial activity, and structural remodeling of synaptic connectivity. There is also a downside of plasticity, that is, maladaptive plasticity, in which there are behavioral losses resulting from plasticity changes in the human brain. Understanding plasticity mechanisms could have major implications in the diagnosis and treatment of ocular diseases, such as retinal disorders, cataract and refractive surgery, amblyopia, and in the evaluation of surgical materials and techniques. Furthermore, eliciting plasticity could open new perspectives in the development of strategies that trigger plasticity for better medical and surgical outcomes.