Time is vision: functional preservation and enhanced capacity for recovery in subacute occipital stroke

Abstract

One Sentence Summary: The first 3 months after an occipital stroke are characterized by a gradual -not sudden -loss of visual perceptual abilities and increased rehabilitative potential if visual discrimination training is administered in the blind field. Abstract:Stroke damage to the primary visual cortex (V1) causes a loss of vision known as hemianopia or cortically-induced blindness (CB). While early, spontaneous, perimetric improvements can occur, by 6 months post-stroke, the deficit is considered chronic and permanent. Despite evidence from sensorimotor stroke showing that early injury responses heighten neuroplastic potential, to date, rehabilitation research has focused only on chronic CB patients. Consequently, little is known about the functional properties of subacute, post-stroke visual systems, and whether they can be harnessed to enhance visual recovery. Here, for the first time, we show that conscious visual discrimination abilities are partially preserved inside subacute, perimetrically-defined blind fields, disappearing by 6 months post-stroke. Complementing this discovery, we show that global motion discrimination training initiated subacutely leads to comparable magnitude of recovery as that initiated in chronic CB. However, it does so 6 times faster, generalizes to deeper, untrained regions of the blind field, and to other [untrained] aspects of motion perception, preventing their degradation upon reaching the chronic period. Untrained subacutes exhibited only spontaneous improvements in perimetry -spontaneous recovery of motion discriminations was never observed.Thus, in CB, the early post-stroke period appears characterized by gradual -rather than suddenloss of visual processing. Subacute training stops this degradation, and is dramatically more efficient at eliciting recovery than identical training in the chronic period. Finally, spontaneous improvements in subacutes appear restricted to luminance detection, whereas recovering discrimination abilities requires deliberate training. Simply stated, after an occipital stroke, "time is VISION".

Alterations of optic tract and retinal structure in patients after thalamic stroke

“…Our current report builds upon our previous report on retinal neurodegeneration following thalamic infarction (Ye et al, 2022) and the fundamental observations that such retrograde transsynaptic neurodegeneration after visual pathway insult follows a distinct time course and pattern (Jindahra et al, 2012;Saionz et al, 2020;Fahrenthold et al, 2021). This study showed that the LI value, which indicates the shrinkage extent of the optic tract (Bridge et al, 2011;Millington et al, 2014;Fahrenthold et al, 2021), altered distinctly compared with age-sex matched stroke-free controls.…”

“…Time since stroke onset (months) and National Institute of Health Stroke Scale (NIHSS) scores were also documented. Since it has been well recognized that the process of TRD is time-dependent (usually occurring significantly from 3 to 7 months to the first few years maximally) (Jindahra et al, 2012), along with the expansion course of poststroke visual deficit, which becomes steady after 6 months (Cavanaugh and Huxlin, 2017;Wang et al, 2017;Saionz et al, 2020), in the following analysis we divided our patients into two subgroups: Group 1 (≤ 6 months) and Group 2 (>6 months). Visual acuity (VA) under illumination was completed for each eye using Snellen charts by an experienced neuro-ophthalmologist (WK) and later converted to the logarithm of the minimum angle of resolution (LogMAR).…”

Changes in perilesional V1 underlie training-induced recovery in cortically-blind patients

“…Aside from improving our scientific understanding of the neural mechanisms underlying visual recovery in CB, our findings are of vital importance for the development of more principled, customized, clinical neurorehabilitation therapies, adapted to the increasing number of people who suffer from cortically-induced visual impairments. Targeting blind-field regions with spared V1 activity might substantially improve the benefits of visual restoration training, particularly in subacute post-stroke periods (i.e., first 3 months) during which our training paradigm can substantially enhance capacity for recovery and preserve visual functions (Saionz et al, 2019).…”

“…CB subjects were trained at select blind-field locations on coarse (left-right) direction discrimination of random dot stimuli and/or vertical-horizontal orientation discrimination of static Gabor patches (Table 1 and Fig.1). For details about the training, testing stimuli and tasks, see our published studies Cavanaugh et al, 2015;Das et al, 2014;Huxlin et al, 2009;Saionz et al, 2019). Training was started at visual-field locations where discrimination performance on either task first dropped to chance (50% correct) during blind-field border mapping (i.e., in lab with online fixation monitoring using an infrared eye tracker [Eyelink 1000 or ISCAN RK464] interfaced with our psychophysical software, to ensure gaze-contingent stimulus presentation).…”

“…Accordingly, some rehabilitation approaches have targeted blindsight to help CB patients recruit these unconscious processes, with some evidence of increased visual performance and awareness post-training (Chokron et al, 2008;Melnick et al, 2016b;Perez and Chokron, 2014;Sahraie et al, 2010;Sahraie et al, 2006). However, training can also recover the ability to discriminate visual information with spatio-temporal properties and motion integration requirements that fail to elicit blindsight Cavanaugh et al, 2015;Das and Huxlin, 2010;Das et al, 2014;Huxlin et al, 2009;Melnick et al, 2016b;Saionz et al, 2019). Thus, "blindsight pathways" may not be the only means by which training can elicit recovery.…”