Spared perilesional V1 activity underlies training-induced recovery of luminance detection sensitivity in cortically-blind patients.

Damage to the primary visual cortex (V1) causes homonymous visual-field loss long considered intractable. Multiple studies now show that perceptual training can restore visual functions in chronic cortically-induced blindness (CB). A popular hypothesis is that training can harness residual visual functions by recruiting intact extrageniculostriate pathways. Training may also induce plastic changes within spared regions of the damaged V1. Here, we link changes in luminance detection sensitivity with retinotopic fMRI activity before and after visual discrimination training in eleven patients with chronic, stroke-induced CB. We show that spared V1 activity representing perimetrically-blind locations prior to training predicts the amount of training-induced recovery of luminance detection sensitivity. Additionally, training results in an enlargement of population receptive fields in perilesional V1, which increases blind-field coverage and may support further recovery with subsequent training. These findings uncover fundamental changes in perilesional V1 cortex underlying training-induced restoration of conscious luminance detection sensitivity in CB.

A woman in her seventies with acute onset of blindness. / En kvinne i 70-årene med akutt blindhet.

BACKGROUND: Dural arteriovenous fistulae are among the most common causes of pulsatile tinnitus. Selective angiography can be necessary for a definitive diagnosis, but in rare cases has been reported to cause sudden cortical blindness. CASE PRESENTATION: We present a woman in her seventies for whom cerebral angiography revealed a dural arteriovenous fistula. Two hours after the angiography she experienced sudden bilateral blindness. A local cause of sudden visual loss was excluded by clinical examination, cerebral bleeding was excluded by CT scan, vascular spasms and occlusions were excluded by CT angiography and acute infarction over the bilateral parieto-occipital cortex was excluded by MRI. The CT scan did, however, show contrast enhancement in the visual cortex from the contrast given during the previously performed cerebral angiography. The patient's vision spontaneously recovered within six days after the angiography, with no residual neurological deficits in her subsequent clinical follow up. Surgery was later performed on her dural arteriovenous fistula, which successfully treated the pulsatile tinnitus. INTERPRETATION: Transient cortical blindness is a rare but dramatic complication after cerebral angiography, thought to be caused by the transient neurotoxic effects of iodine-containing contrast agents. When other causes of sudden blindness are excluded, the patient can be reassured about the excellent prognosis for this condition.

Cerebral Visual Impairment Characterized by Abnormal Visual Orienting Behavior With Preserved Visual Cortical Activation.

Purpose: Children with cerebral visual impairment (CVI) often have abnormal visual orienting behaviors due to impaired or damaged visual cortex. Alternatively, visual-cortical function is intact but visual information is not transformed downstream into an appropriate oculomotor output (visuomotor dysfunction). We examined visual, anatomic, and oculomotor assessments to distinguish visuomotor dysfunction from CVI associated with severely reduced visual-cortical response. Methods: We reviewed the medical records from children with CVI having abnormal visual orienting behaviors, normal ocular examinations, and born near term. Relevant data were visual evoked potentials (VEPs), Teller card acuity, eye movements recorded by video-oculography (VOG), and neuroimaging (magnetic resonance imaging [MRI]) including diffusion tensor imaging (DTI) tractography. Results: Thirty subjects had visuomotor dysfunction based on a normal VEP; of these 33% had a normal MRI and 67% had white matter abnormalities associated with metabolic disease and/or decreased volume of brain parenchyma. VOG recordings showed smooth pursuit gains were uniformly reduced and saccades were dysmetric but followed the main sequence. Ten subjects had severe CVI based on VEPs at noise levels; visual acuities and MRI findings overlapped those of the visuomotor dysfunction group. Developmental delay, seizures, microcephaly, and hypotonia were common across all groups. All subjects with an abnormal conventional MRI had abnormal metrics on DTI tractography from the occipital lobe. Conclusions: A subset of patients with CVI have abnormal visual orienting behaviors despite a normal VEP (visuomotor dysfunction). A majority have abnormal white matter metrics on tractography suggesting a downstream defect in sensorimotor transformation. Clinically, visuomotor dysfunction is indistinguishable from severe CVI.

Case Report: Transient cortical blindness following coronary angiography.

Temporary blindness, also known as transient cortical blindness, is an uncommon impediment of contrast agent usage during angiography procedures. The occurrence of blindness after a cardiac catheterization procedure is rare and its pathophysiology remains largely speculative. The most probable mechanism seems to be contrast agent-related disruption of the blood-brain barrier, possibly initiated by several predisposing factors. This case reports a 52-year-old man with transient vision loss that occurred following coronary angiography. Brain magnetic resonance imaging (MRI) showed no acute pathology and his vision spontaneously returned within approximately 15 hours post-procedure without any requirement of specific therapy. Suggesting that transient cortical blindness may have occurred following coronary angiography which subsequently self-resolved.

Ceguera cortical como manifestación inicial de endocarditis trombótica no bacteriana / Cortical blindness as initial manifestation of nonbacterial thrombotic endocarditis

La endocarditis trombótica no bacteriana, antiguamente conocida como endocarditis marántica, es una entidad infrecuente en la que se desarrollan vegetaciones estériles, compuestas por fibrina en las válvulas del corazón. Suele diagnosticarse en el momento de la autopsia o en enfermedades oncológicas avanzadas. Las neoplasias malignas más frecuentemente asociadas con esta entidad son las de pulmón, páncreas, estómago y adenocarcinomas de origen primario desconocido. Es necesario descartar la endocarditis infecciosa y establecer la presencia de vegetaciones valvulares mediante ecocardiografía. Presentamos el caso de una paciente con diagnóstico reciente de adenocarcinoma de estómago en estadio avanzado que presentó ceguera cortical e imágenes compatibles con isquemia cerebral. El ecocardiograma transesofágico mostró dos vegetaciones en válvula mitral. Los hemocultivos fueron negativos. Se enfatiza la importancia de sospechar endocarditis trombótica no bacteriana en enfermos con cáncer y embolismo sistémico.

Nonbacterial thrombotic endocarditis, formerly known as marantic endocarditis, it is an infrequent entity in which sterile, fibrin vegetations develop on heart valve leaflets. It is often diagnosed at the time of autopsy or in late-stage malignancies. The most common malignancies associated with nonbacterial thrombotic endocarditis are lung, pancreatic, gastric cancer and adenocarcinomas of an unknown primary site. Diagnosis requires ruling out infective endocarditis and establishing the presence of valvular vegetations using echocardiography. We report the case of a patient with a recent diagnosis of advanced gastric adenocarcinoma who presented with cortical blindness. The computed tomography was compatible with cerebral ischemia. The transoesophageal echocardiogram showed two vegetations in mitral valve. Blood cultures were negative. We emphasize the importance of suspecting nonbacterial thrombotic endocarditis in patients with cancer and systemic embolism.

[Cortical blindness as initial manifestation of nonbacterial thrombotic endocarditis]. / Ceguera cortical como manifestación inicial de endocarditis trombótica no bacteriana.

Nonbacterial thrombotic endocarditis, formerly known as marantic endocarditis, it is an infrequent entity in which sterile, fibrin vegetations develop on heart valve leaflets. It is often diagnosed at the time of autopsy or in latestage malignancies. The most common malignancies associated with nonbacterial thrombotic endocarditis are lung, pancreatic, gastric cancer and adenocarcinomas of an unknown primary site. Diagnosis requires ruling out infective endocarditis and establishing the presence of valvular vegetations using echocardiography. We report the case of a patient with a recent diagnosis of advanced gastric adenocarcinoma who presented with cortical blindness. The computed tomography was compatible with cerebral ischemia. The transoesophageal echocardiogram showed two vegetations in mitral valve. Blood cultures were negative. We emphasize the importance of suspecting nonbacterial thrombotic endocarditis in patients with cancer and systemic embolism.

Affective blindsight relies on low spatial frequencies.

The human brain can process facial expressions of emotions rapidly and without awareness. Several studies in patients with damage to their primary visual cortices have shown that they may be able to guess the emotional expression on a face despite their cortical blindness. This non-conscious processing, called affective blindsight, may arise through an intact subcortical visual route that leads from the superior colliculus to the pulvinar, and thence to the amygdala. This pathway is thought to process the crude visual information conveyed by the low spatial frequencies of the stimuli. In order to investigate whether this is the case, we studied a patient (TN) with bilateral cortical blindness and affective blindsight. An fMRI paradigm was performed in which fearful and neutral expressions were presented using faces that were either unfiltered, or filtered to remove high or low spatial frequencies. Unfiltered fearful faces produced right amygdala activation although the patient was unaware of the presence of the stimuli. More importantly, the low spatial frequency components of fearful faces continued to produce right amygdala activity while the high spatial frequency components did not. Our findings thus confirm that the visual information present in the low spatial frequencies is sufficient to produce affective blindsight, further suggesting that its existence could rely on the subcortical colliculo-pulvino-amygdalar pathway.

Subcortical pathways to extrastriate visual cortex underlie residual vision following bilateral damage to V1.

Residual vision, or blindsight, following damage to the primary visual cortex (V1) has been investigated for almost half a century. While there have been many studies of patients with unilateral damage to V1, far fewer have examined bilateral damage, mainly due to the rarity of such patients. Here we re-examine the residual visual function and underlying pathways of previously studied patient SBR who, as a young adult, suffered bilateral damage restricted to V1 which rendered him cortically blind. While earlier work compared his visual cortex to healthy, sighted participants, here we consider how his visual responses and connections compare to patients with unilateral damage to V1 in addition to sighted participants. Detection of drifting Gabor patches of different contrasts (1%, 5%, 10%, 50% and 100%) was tested in SBR and a group of eight patients with unilateral damage to V1. Performance was compared to the neural activation in motion area hMT+ measured using functional magnetic resonance imaging. Diffusion tractography was also used to determine the white matter microstructure of the visual pathways in all participants. Like the patients with unilateral damage, patient SBR showed increased % BOLD signal change to the high contrast stimuli that he could detect compared to the lower contrast stimuli that were not detectable. Diffusion tractography suggests this information is conveyed by a direct pathway between the lateral geniculate nucleus (LGN) and hMT+ since this pathway had microstructure that was comparable to the healthy control group. In contrast, the pathway between LGN and V1 had reduced integrity compared to controls. A further finding of note was that, unlike control participants, SBR showed similar patterns of contralateral and ipsilateral activity in hMT+, in addition to healthy white matter microstructure in the tract connecting hMT+ between the two hemispheres. This raises the possibility of increased connectivity between the two hemispheres in the absence of V1 input. In conclusion, the pattern of visual function and anatomy in bilateral cortical damage is comparable to that seen in a group of patients with unilateral damage. Thus, while the intact hemisphere may play a role in residual vision in patients with unilateral damage, its influence is not evident with the methodology employed here.

Feature-based attention potentiates recovery of fine direction discrimination in cortically blind patients.

Training chronic, cortically-blind (CB) patients on a coarse [left-right] direction discrimination and integration (CDDI) task recovers performance on this task at trained, blind field locations. However, fine direction difference (FDD) thresholds remain elevated at these locations, limiting the usefulness of recovered vision in daily life. Here, we asked if this FDD impairment can be overcome by training CB subjects with endogenous, feature-based attention (FBA) cues. Ten CB subjects were recruited and trained on CDDI and FDD with an FBA cue or FDD with a neutral cue. After completion of each training protocol, FDD thresholds were re-measured with both neutral and FBA cues at trained, blind-field locations and at corresponding, intact-field locations. In intact portions of the visual field, FDD thresholds were lower when tested with FBA than neutral cues. Training subjects in the blind field on the CDDI task improved FDD performance to the point that a threshold could be measured, but these locations remained impaired relative to the intact field. FDD training with neutral cues resulted in better blind field FDD thresholds than CDDI training, but thresholds remained impaired relative to intact field levels, regardless of testing cue condition. Importantly, training FDD in the blind field with FBA lowered FDD thresholds relative to CDDI training, and allowed the blind field to reach thresholds similar to the intact field, even when FBA trained subjects were tested with a neutral rather than FBA cue. Finally, FDD training appeared to also recover normal integration thresholds at trained, blind-field locations, providing an interesting double dissociation with respect to CDDI training. In summary, mechanisms governing FBA appear to function normally in both intact and impaired regions of the visual field following V1 damage. Our results mark the first time that FDD thresholds in CB fields have been seen to reach intact field levels of performance. Moreover, FBA can be leveraged during visual training to recover normal, fine direction discrimination and integration performance at trained, blind-field locations, potentiating visual recovery of more complex and precise aspects of motion perception in cortically-blinded fields.

Functional neuroanatomy of blindsight revealed by activation likelihood estimation meta-analysis.

Blindsight, the residual abilities of patients with cortical blindness to respond proficiently to stimuli they do not consciously acknowledge, offers a unique opportunity to study the functional and anatomical mechanisms sustaining visual awareness. Over decades, the phenomenon has been documented in a wide number of different patients, across independent laboratories, and for a variety of tasks and stimulus properties. Nevertheless, the functional neuroanatomy of blindsight remains elusive and alternative proposals have been put forth. To tackle this issue from a novel perspective, we performed a quantitative Activation Likelihood Estimation (ALE) meta-analysis on the neuroimaging literature available on blindsight. Significant activity was reported in subcortical structures, such as the superior colliculus, pulvinar and amygdala, as well as in cortical extrastriate areas along the dorsal and ventral visual stream. This data-driven functional network collectively defines the extant neural fingerprint of blindsight. To further characterize the unique combination of segregation and integration in brain networks engaged in blindsight, we measured the relationship between active areas and experimental features in the original studies, their clustering and hierarchical organization. Results support a network-based organization in the functional neuroanatomy of blindsight, which likely reflects the intersection of different stimulus properties and behavioural tasks examined. We suggest that the conceptualization of blindsight as a constellation of multiple nonconscious visual abilities is better apt as a summary of present-day wisdom, thereby mirroring the variety of existing V1-independent pathway and their different functional roles.

Psychophysical and neuroimaging responses to moving stimuli in a patient with the Riddoch phenomenon due to bilateral visual cortex lesions.

Patients with injury to early visual cortex or its inputs can display the Riddoch phenomenon: preserved awareness for moving but not stationary stimuli. We provide a detailed case report of a patient with the Riddoch phenomenon, MC. MC has extensive bilateral lesions to occipitotemporal cortex that include most early visual cortex and complete blindness in visual field perimetry testing with static targets. Nevertheless, she shows a remarkably robust preserved ability to perceive motion, enabling her to navigate through cluttered environments and perform actions like catching moving balls. Comparisons of MC's structural magnetic resonance imaging (MRI) data to a probabilistic atlas based on controls reveals that MC's lesions encompass the posterior, lateral, and ventral early visual cortex bilaterally (V1, V2, V3A/B, LO1/2, TO1/2, hV4 and VO1 in both hemispheres) as well as more extensive damage to right parietal (inferior parietal lobule) and left ventral occipitotemporal cortex (VO1, PHC1/2). She shows some sparing of anterior occipital cortex, which may account for her ability to see moving targets beyond ~15 degrees eccentricity during perimetry. Most strikingly, functional and structural MRI revealed robust and reliable spared functionality of the middle temporal motion complex (MT+) bilaterally. Moreover, consistent with her preserved ability to discriminate motion direction in psychophysical testing, MC also shows direction-selective adaptation in MT+. A variety of tests did not enable us to discern whether input to MT+ was driven by her spared anterior occipital cortex or subcortical inputs. Nevertheless, MC shows rich motion perception despite profoundly impaired static and form vision, combined with clear preservation of activation in MT+, thus supporting the role of MT+ in the Riddoch phenomenon.

More than blindsight: Case report of a child with extraordinary visual capacity following perinatal bilateral occipital lobe injury.

Injury to the primary visual cortex (V1, striate cortex) and the geniculostriate pathway in adults results in cortical blindness, abolishing conscious visual perception. Early studies by Larry Weiskrantz and colleagues demonstrated that some patients with an occipital-lobe injury exhibited a degree of unconscious vision and visually-guided behaviour within the blind field. A more recent focus has been the observed phenomenon whereby early-life injury to V1 often results in the preservation of visual perception in both monkeys and humans. These findings initiated a concerted effort on multiple fronts, including nonhuman primate studies, to uncover the neural substrate/s of the spared conscious vision. In both adult and early-life cases of V1 injury, evidence suggests the involvement of the Middle Temporal area (MT) of the extrastriate visual cortex, which is an integral component area of the dorsal stream and is also associated with visually-guided behaviors. Because of the limited number of early-life V1 injury cases for humans, the outstanding question in the field is what secondary visual pathways are responsible for this extraordinary capacity? Here we report for the first time a case of a child (B.I.) who suffered a bilateral occipital-lobe injury in the first two weeks postnatally due to medium-chain acyl-Co-A dehydrogenase deficiency. At 6 years of age, B.I. underwent a battery of neurophysiological tests, as well as structural and diffusion MRI and ophthalmic examination at 7 years. Despite the extensive bilateral occipital cortical damage, B.I. has extensive conscious visual abilities, is not blind, and can use vision to navigate his environment. Furthermore, unlike blindsight patients, he can readily and consciously identify happy and neutral faces and colors, tasks associated with ventral stream processing. These findings suggest significant re-routing of visual information. To identify the putative visual pathway/s responsible for this ability, MRI tractography of secondary visual pathways connecting MT with the lateral geniculate nucleus (LGN) and the inferior pulvinar (PI) were analysed. Results revealed an increased PI-MT pathway in the left hemisphere, suggesting that this pulvinar relay could be the neural pathway affording the preserved visual capacity following an early-life lesion of V1. These findings corroborate anatomical evidence from monkeys showing an enhanced PI-MT pathway following an early-life lesion of V1, compared to adults.

Bioccipital Lobe Hypoperfusion and Anton's Syndrome Resolution with Intravenous Thrombolysis.

BACKGROUND: Anton's syndrome is a rare neurological disorder characterized by a combination of visual anosognosia and confabulation of visual experience, most often seen after bilateral ischemic damage to the posterior occipital cortex. CASE REPORT: We report the first case of an acute synchronous P2 occlusion as confirmed by multiparametric computed tomography (CT) including perfusion. After the administration of Recombinant tissue plasminogen activator (rtPA), Anton's syndrome completely resolved. CONCLUSION: Multiparametric CT imaging may aid in quickly proving the underlying stroke in Anton's syndrome, especially helpful considering the discrepancy between the patient's perception and clinical examination results.

Transient Cortical Blindness Associated with Endovascular Procedures for Intracranial Aneurysms.

BACKGROUND: We presented 3 cases of transient cortical blindness secondary to contrast medium toxicity after endovascular procedures for intracranial aneurysms. We also reviewed the literature and found 12 cases of contrast-induced cortical blindness after endovascular procedures for intracranial aneurysms. CASE DESCRIPTION: Two patients (cases 1 and 2) noted bilateral blindness 5 and 6 hours, respectively, after awakening from general anesthesia following aneurysm treatment. The third patient (case 3) noted bilateral blindness during vertebral angiography under local anesthesia. Immediate angiography was performed in case 1 and showed no arterial occlusion. Computed tomography was performed in case 2 and showed brain edema. Magnetic resonance imaging was performed in all 3 cases, and cases 2 and 3 showed abnormal presentation on fluid attenuated inversion recovery sequences. With the use of corticosteroid and intravenous hydration, cortical blindness resolved within 1 week in 2 patients (Cases 1 and 2). The remaining patient (case 3) had incomplete quadrantanopia 3 months after blindness onset. CONCLUSIONS: Based on our experience and the literature reports, we advocate corticosteroid and intravenous hydration for patients with contrast-induced cortical blindness after endovascular procedures for intracranial aneurysms.

Anton-Babinski syndrome, case report. / Ceguera de Anton-Babinski, a propósito de un caso.

CLINICAL CASE: A 22 year-old woman complained about blurred vision after an episode of recovered cardiorespiratory arrest. She had bilateral low visual acuity («count fingers¼) and no ophthalmological or visual pathways changes. She also had an apparent lack of awareness of the deficit. The Magnetic Resonance Imaging (MRI) showed ischaemic changes in both occipital lobes. As a result, she was diagnosed with Anton-Babinski syndrome. DISCUSSION: This is a rare disease that should be suspected in strange or poorly congruent visual loss. It is usually due to an ischaemic injury in this region of brain, manifesting itself with low vision not perceived by the patient (visual confabulation). It can simulate a non-organic visual loss or psychiatric disease.

Cortical blindness as a rare presentation of hemorrhagic cerebral hyperperfusion syndrome following vertebral angioplasty.

Cerebral hyperperfusion syndrome (CHS) is a well-documented complication after carotid endarterectomy or stenting. In contrast, CHS following vertebral revascularization is extremely rare. Here we present a case of a 77-year-old man with high-grade vertebral stenosis who subsequently underwent balloon angioplasty, complicated by hemorrhagic CHS manifesting as cortical blindness, although strict postoperative blood pressure control was administered. To our knowledge, cortical blindness as a presentation of hemorrhagic CHS has not previously been reported. This study highlights the fact that identifying high-risk patients, as well as making an individual therapeutic plan, is important prior to revascularization. Further studies are needed to elucidate the exact mechanism of this condition and thereby prevent it.