Visual Field Stimulation Research Articles

An open platform for visual stimulation of insects.

To study how the nervous system processes visual information, experimenters must record neural activity while delivering visual stimuli in a controlled fashion. In animals with a nearly panoramic field of view, such as flies, precise stimulation of the entire visual field is challenging. We describe a projector-based device for stimulation of the insect visual system under a microscope. The device is based on a bowl-shaped screen that provides a wide and nearly distortion-free field of view. It is compact, cheap, easy to assemble, and easy to operate using the included open-source software for stimulus generation. We validate the virtual reality system technically and demonstrate its capabilities in a series of experiments at two levels: the cellular, by measuring the membrane potential responses of visual interneurons; and the organismal, by recording optomotor and fixation behavior of Drosophila melanogaster in tethered flight. Our experiments reveal the importance of stimulating the visual system of an insect with a wide field of view, and we provide a simple solution to do so.

A sub-region combination scheme for spatial coding in a high-frequency SSVEP-based BCI

Objective. In studying the spatial coding mechanism of visual evoked potentials, it is significant to construct a model that shows the relationship between steady-state visual evoked potential (SSVEP) responses to the local and global visual field stimulation. In order to investigate whether SSVEPs produced by sub-region stimulation can predict that produced by joint region stimulation, a sub-region combination scheme for spatial coding in a high-frequency SSVEP-based brain-computer interface (BCI) is developed innovatively. Approach. An annular visual field is divided equally into eight sub-regions. The 60 Hz visual stimuli in different sub-regions and joint regions are presented separately to participants. The SSVEP produced by the sub-region stimulation is superimposed to simulate the SSVEP produced by the joint region stimulation with different spatial combinations. A four-class spatially-coded BCI paradigm is used to evaluate the simulated classification performance, and the performance ranking of all simulated SSVEPs is obtained. Six representative stimulus patterns from two performance levels and three stimulus areas are applied to the online BCI system for each participant. Main results. The experimental result shows that the proposed scheme can implement a spatially-coded visual BCI system and realize satisfactory performance with imperceptible flicker. Offline analysis indicates that the classification accuracy and information transfer rate (ITR) are 89.69 ± 8.75% and 24.35 ± 7.09 bits min−1 with 3 s data length under the 3/8 stimulus area. The online BCI system reaches an average classification accuracy of 87.50 ± 9.13% with 3 s data length, resulting in an ITR of 22.48 ± 6.71 bits min−1 under the 3/8 stimulus area. Significance. This study proves the feasibility of using the sub-region’s response to predict the joint region’s response. It has the potential to extend to other frequency bands and lays a foundation for future research on more complex spatial coding methods.

Dual-Brain Psychology: A novel theory and treatment based on cerebral laterality and psychopathology

Dual-Brain Psychology is a theory and its clinical applications that come out of the author's clinical observations and from the Split-brain Studies. The theory posits, based on decades of rigorous, peer-reviewed experiments and clinical reports, that, in most patients, one brain's cerebral hemisphere (either left or right) when stimulated by simple lateral visual field stimulation, or unilateral transcranial photobiomodulation, reveals a dramatic change in personality such that stimulating one hemisphere evokes, as a trait, a personality that is more childlike and more presently affected by childhood maltreatments that are usually not presently appreciated but are the proximal cause of the patient's symptoms. The personality associated with the other hemisphere is much more mature, less affected by the traumas, and less symptomatic. The theory can be applied to in-depth psychotherapy in which the focus is on helping the troubled side to bear and process the traumas with the help of the therapist and the healthier personality. A person's symptoms can be evoked to aid the psychotherapy with hemispheric stimulation and the relationship between the dual personalities can be transformed from conflicted and sabotaging to cooperating toward overall health. Stimulating the positive hemisphere in most therapy patients rapidly relieves symptoms such as anxiety, depression, or substance cravings. Two randomized controlled trials used unilateral transcranial photobiomodulation to the positive hemisphere as a stand-alone treatment for opioid cravings and both revealed high effect sizes. The theory is supported by brain imaging and rTMS studies. It is the first psychological theory and application that comes out of and is supported by rigorous peer-reviewed experimentation.

Altered visual population receptive fields in human albinism

Albinism is a congenital disorder where misrouting of the optic nerves at the chiasm gives rise to abnormal visual field representations in occipital cortex. In typical human development, the left occipital cortex receives retinal input predominantly from the right visual field, and vice-versa. In albinism, there is a more complete decussation of optic nerve fibers at the chiasm, resulting in partial representation of the temporal hemiretina (ipsilateral visual field) in the contralateral hemisphere. In this study, we characterize the receptive field properties for these abnormal representations by conducting detailed fMRI population receptive field mapping in a rare subset of participants with albinism and no ocular nystagmus. We find a nasal bias for receptive field positions in the abnormal temporal hemiretina representation. In addition, by modelling responses to bilateral visual field stimulation in the overlap zone, we found evidence in favor of discrete unilateral receptive fields, suggesting a conservative pattern of spatial selectivity in the presence of abnormal retinal input.

Stimulus-Driven Cortical Hyperexcitability in Individuals with Charles Bonnet Hallucinations

Throughout the lifespan, the cerebral cortex adapts its structure and function in response to changing sensory input [1, 2]. Whilst such changes are typically adaptive, they can be maladaptive when they follow damage to the peripheral nervous system, including phantom limb pain and tinnitus [3, 4]. An intriguing example occurs in individuals with acquired ocular pathologies-most commonly age-related macular degeneration (MD) [5]-who lose their foveal vision but retain intact acuity in the peripheral visual field. Up to 40% of ocular pathology patients develop long-term hallucinations involving flashes of light, shapes, or geometric patterns and/or complex hallucinations, including faces, animals, or entire scenes, a condition known as Charles Bonnet Syndrome (CBS) [6, 7, 8]. Though CBS was first described over 250 years ago [9, 10], the neural basis for the hallucinations remains unclear, with no satisfactory explanation as to why some individuals develop hallucinations, while many do not. An influential but untested hypothesis for the visual hallucinations in CBS is that retinal deafferentation causes hyperexcitability in early visual cortex. To assess this, we investigated electrophysiological responses to peripheral visual field stimulation in MD patients with and without hallucinations and in matched controls without ocular pathology. Participants performed a concurrent attention task within intact portions of their peripheral visual field, while ignoring flickering checkerboards that drove periodic electrophysiological responses. CBS individuals showed strikingly elevated visual cortical responses to peripheral field stimulation compared with patients without hallucinations and controls, providing direct support for the hypothesis of visual cortical hyperexcitability in CBS.

A bi-planar coil system for nulling background magnetic fields in scalp mounted magnetoencephalography

Small, commercially-available Optically Pumped Magnetometers (OPMs) can be used to construct a wearable Magnetoencephalography (MEG) system that allows large head movements to be made during recording. The small dynamic range of these sensors however means that movement in the residual static magnetic field found inside typical Magnetically Shielded Rooms (MSRs) can saturate the sensor outputs, rendering the data unusable. This problem can be ameliorated by using a set of electromagnetic coils to attenuate the spatially-varying remnant field. Here, an array of bi-planar coils, which produce an open and accessible scanning environment, was designed and constructed. The coils were designed using a harmonic minimisation method previously used for gradient coil design in Magnetic Resonance Imaging (MRI). Six coils were constructed to null Bx, By and Bz as well as the three dominant field gradients dBx/dz, dBy/dz and dBz/dz. The coils produce homogeneous (within ±5%) fields or field gradients over a volume of 40 × 40 × 40 cm3. This volume is sufficient to contain an array of OPMs, mounted in a 3D-printed scanner-cast, during basic and natural movements. Automated control of the coils using reference sensor measurements allows reduction of the largest component of the static field (Bx) from 21.8 ± 0.2 nT to 0.47 ± 0.08 nT. The largest gradient (dBx/dz) was reduced from 7.4 nT/m to 0.55 nT/m. High precision optical tracking allowed experiments involving controlled and measured head movements, which revealed that a rotation of the scanner-cast by ±34° and translation of ±9.7 cm of the OPMs in this field generated only a 1 nT magnetic field variation across the OPM array, when field nulling was applied. This variation could be further reduced to 0.04 nT by linear regression of field variations that were correlated with the measured motion parameters. To demonstrate the effectiveness of the bi-planar coil field cancellation system in a real MEG experiment, a novel measurement of retinotopy was investigated, where the stimulus remains fixed and head movements made by the subject shift the visual presentation to the lower left or right quadrants of the field of view. Left and right visual field stimulation produced the expected responses in the opposing hemisphere. This simple demonstration shows that the bi-planar coil system allows accurate OPM-MEG recordings to be made on an unrestrained subject.

Early retinotopic responses to violations of emotion–location associations may depend on conscious awareness

ABSTRACTReports of modulations of early visual processing suggest that retinotopic visual cortex may actively predict upcoming stimuli. We tested this idea by showing healthy human participants images of human faces at fixation, with different emotional expressions predicting stimuli in either the upper or the lower visual field. On infrequent test trials, emotional faces were followed by combined stimulation of upper and lower visual fields, thus violating previously established associations. Results showed no effects of such violations at the level of the retinotopic C1 of the visual evoked potential over the full sample. However, when separating participants who became aware of these associations from those who did not, we observed significant group differences during extrastriate processing of emotional faces, with inverse solution results indicating stronger activity in unaware subjects throughout the ventral visual stream. Moreover, within-group comparisons showed that the same peripheral stimuli elicited differential activity patterns during the C1 interval, depending on which stimulus elements were predictable. This effect was selectively observed in manipulation-aware subjects. Our results provide preliminary evidence for the notion that early visual processing stages implement predictions of upcoming events. They also point to conscious awareness as a moderator of predictive coding.

Detecting Glaucoma With a Portable Brain-Computer Interface for Objective Assessment of Visual Function Loss

The current assessment of visual field loss in diseases such as glaucoma is affected by the subjectivity of patient responses and the lack of portability of standard perimeters. To describe the development and initial validation of a portable brain-computer interface (BCI) for objectively assessing visual function loss. This case-control study involved 62 eyes of 33 patients with glaucoma and 30 eyes of 17 healthy participants. Glaucoma was diagnosed based on a masked grading of optic disc stereophotographs. All participants underwent testing with a BCI device and standard automated perimetry (SAP) within 3 months. The BCI device integrates wearable, wireless, dry electroencephalogram and electrooculogram systems and a cellphone-based head-mounted display to enable the detection of multifocal steady state visual-evoked potentials associated with visual field stimulation. The performances of global and sectoral multifocal steady state visual-evoked potentials metrics to discriminate glaucomatous from healthy eyes were compared with global and sectoral SAP parameters. The repeatability of the BCI device measurements was assessed by collecting results of repeated testing in 20 eyes of 10 participants with glaucoma for 3 sessions of measurements separated by weekly intervals. Receiver operating characteristic curves summarizing diagnostic accuracy. Intraclass correlation coefficients and coefficients of variation for assessing repeatability. Among the 33 participants with glaucoma, 19 (58%) were white, 12 (36%) were black, and 2 (6%) were Asian, while among the 17 participants with healthy eyes, 9 (53%) were white, 8 (47%) were black, and none were Asian. The receiver operating characteristic curve area for the global BCI multifocal steady state visual-evoked potentials parameter was 0.92 (95% CI, 0.86-0.96), which was larger than for SAP mean deviation (area under the curve, 0.81; 95% CI, 0.72-0.90), SAP mean sensitivity (area under the curve, 0.80; 95% CI, 0.69-0.88; P = .03), and SAP pattern standard deviation (area under the curve, 0.77; 95% CI, 0.66-0.87; P = .01). No statistically significant differences were seen for the sectoral measurements between the BCI and SAP. Intraclass coefficients for global and sectoral parameters ranged from 0.74 to 0.92, and mean coefficients of variation ranged from 3.03% to 7.45%. The BCI device may be useful for assessing the electrical brain responses associated with visual field stimulation. The device discriminated eyes with glaucomatous neuropathy from healthy eyes in a clinically based setting. Further studies should investigate the feasibility of the BCI device for home-based testing as well as for detecting visual function loss over time.

Influence of BOLD Contributions to Diffusion fMRI Activation of the Visual Cortex.

Reliance on the hemodynamic response as a surrogate marker of neural activity imposes an intrinsic limit on the spatial specificity of functional MRI. An alternative approach based on diffusion-weighted functional MRI (DfMRI) has been reported as a contrast less reliant on hemodynamic effects, however current evidence suggests that both hemodynamic and unique neural sources contribute to the diffusion signal. Here we compare activation patterns obtained with the standard blood oxygenation level-dependent (BOLD) contrast to DfMRI in order to gain a deeper understanding of how the BOLD proportion contributes to the observable diffusion signal. Both individual and group-level activation patterns obtained with DfMRI and BOLD to a visual field stimulation paradigm were analyzed. At the individual level, the DfMRI contrast showed a strong, positive relationship between the volumes of cortex activated in response to quadrant- and hemi-field visual stimulation. This was not observed in the corresponding BOLD experiment. Overall, the DfMRI response indicated less between-subject variability, with random effects analyses demonstrating higher statistical values at the peak voxel for DfMRI. Furthermore, the spatial extent of the activation was more restricted to the primary visual region for DfMRI than BOLD. However, the diffusion signal was sensitive to the hemodynamic response in a manner dependent on experimental manipulation. It was also limited by its low signal-to-noise ratio (SNR), demonstrating lower sensitivity than BOLD. Together these findings both support DfMRI as a contrast that bears a closer spatial relationship to the underlying neural activity than BOLD, and raise important caveats regarding its utilization. Models explaining the DfMRI signal change need to consider the dynamic vascular contributions that may vary with neural activity.

Melanopsin-mediated post-illumination pupil response in the peripheral retina.

Intrinsically photosensitive retinal ganglion cells (ipRGCs) regulate pupil size by integrating extrinsic rod and cone signals with intrinsic melanopsin-mediated phototransduction. Light adapted pupil diameter is determined by the corneal flux density (CFD), and for central visual field stimulation the melanopsin-mediated post-illumination pupil response (PIPR) follows this same CFD relationship. Rods, cones, and ipRGCs vary in size, density, and distribution across the retina, but how these differences affect the amplitude and timing of the extrinsic and intrinsic pupil light reflex in the central and peripheral retina is unknown. We determined the relationship between stimulus area and photon flux with stimuli constant for CFD, irradiance, or area at central (0°) and peripheral (20°) eccentricities with high and low melanopsin excitation. We show that the pupil constriction amplitude was similar at both eccentricities and the time to minimum diameter increased as melanopsin excitation increased. In contrast, the peripheral PIPR follows a CFD relationship but with lower amplitude compared with that at the fovea. This indicates differences in the spatial and temporal characteristics of extrinsic and intrinsic ipRGC inputs to the pupil control pathway for the central and peripheral retina. The eccentricity-dependent change in PIPR amplitude may be analogous to the hill of vision observed in visual perimetry; such knowledge is an important precursor to the development of pupil perimetry paradigms to measure the PIPR in select regions of the visual field.

Reaction Time in a Visual 4-Choice Reaction Time Task: ERP Effects of Motor Preparation and Hemispheric Involvement.

Reaction time (RT), the most common measure of CNS efficiency, shows intra- and inter-individual variability. This may be accounted for by hemispheric specialization, individual neuroanatomy, and transient functional fluctuations between trials. To explore RT on these three levels, ERPs were measured in a visual 4-choice RT task with lateralized stimuli (left lateral, left middle, right middle, and right lateral) in 28 healthy right-handed subjects. We analyzed behavioral data, ERP microstates (MS), N1 and P3 components, and trial-by-trial variance. Across subjects, the N1 component was contralateral to the stimulation side. N1-MSs were stronger over the left hemisphere, and middle stimulation evoked stronger activation than lateral stimulation in both hemispheres. The P3 was larger for the right visual field stimulation. RTs were shorter for the right visual hemifield stimulation/right hand responses. Within subjects, covariance analysis of single trial ERPs with RTs showed consistent lateralized predictors of RT over the motor cortex (MC) in the 112-248ms interval. Decreased RTs were related to negativity over the MC contralateral to the stimulation side, an effect that could be interpreted as the lateralized readiness potential (LRP), and which was strongest for right side stimulation. The covariance analysis linking individual mean RTs and individual mean ERPs showed a frontal negativity and an occipital positivity correlating with decreased RTs in the 212-232ms interval. We concluded that a particular RT is a composite measure that depends on the appropriateness of the motor preparation to a particular response and on stimulus lateralization that selectively involves a particular hemisphere.

Soft tissue treatment and neurological stimulation to increase range of motion after total knee replacement surgery

Soft tissue treatment and neurological stimulation to increase range of motion after total knee replacement surgery

Effects of refractive errors on visual evoked magnetic fields.

BackgroundThe latency and amplitude of visual evoked cortical responses are known to be affected by refractive states, suggesting that they may be used as an objective index of refractive errors. In order to establish an easy and reliable method for this purpose, we herein examined the effects of refractive errors on visual evoked magnetic fields (VEFs).MethodsBinocular VEFs following the presentation of a simple grating of 0.16 cd/m2 in the lower visual field were recorded in 12 healthy volunteers and compared among four refractive states: 0D, +1D, +2D, and +4D, by using plus lenses.ResultsThe low-luminance visual stimulus evoked a main MEG response at approximately 120 ms (M100) that reversed its polarity between the upper and lower visual field stimulations and originated from the occipital midline area. When refractive errors were induced by plus lenses, the latency of M100 increased, while its amplitude decreased with an increase in power of the lens. Differences from the control condition (+0D) were significant for all three lenses examined. The results of dipole analyses showed that evoked fields for the control (+0D) condition were explainable by one dipole in the primary visual cortex (V1), while other sources, presumably in V3 or V6, slightly contributed to shape M100 for the +2D or +4D condition.ConclusionsThe present results showed that the latency and amplitude of M100 are both useful indicators for assessing refractive states. The contribution of neural sources other than V1 to M100 was modest under the 0D and +1D conditions. By considering the nature of the activity of M100 including its high sensitivity to a spatial frequency and lower visual field dominance, a simple low-luminance grating stimulus at an optimal spatial frequency in the lower visual field appears appropriate for obtaining data on high S/N ratios and reducing the load on subjects.

Balance in Parkinson's disease patients changing the visual input

AbstractThe description of the postural responses in Parkinson's disease patients when visual information changes from a stable to a moving visual field analyzing the impact on balance in these patients. Methods (Clinical)Limits of Stability, Body center of pressure and balance functional reserve were measured by means of the force platform in 24 Parkinson's patients in stages 1 and 2 of the Boher classification and 19 volunteers as a control group. Both groups were stimulated with 1-Static visual field and 2-horizontal optokinetic stimulation using a virtual reality system. Postural responses were analyzed using the inverted pendulum as mathematical model. ResultsWhile the control group didn't show significant differences on the postural control between the two sensory conditions (COP p=0.0017, BFR p=0.0025), Parkinson's patients presented significant differences in the area of the center of pressure and the balance functional reserve values between static visual field and optokinetic stimulation. (COP p=0.0017, BFR p=0.0025). ConclusionsThe results support the hypothesis about the influence of the changes in the visual information in triggering balance control disorders in Parkinson's patients. It is discussed the interest of these fact in the assessment and the rehabilitation programs of this disease.

Features of the Retinotopic Representation in the Visual Wulst of a Laterally Eyed Bird, the Zebra Finch (Taeniopygia guttata)

The visual wulst of the zebra finch comprises at least two retinotopic maps of the contralateral eye. As yet, it is not known how much of the visual field is represented in the wulst neuronal maps, how the organization of the maps is related to the retinal architecture, and how information from the ipsilateral eye is involved in the activation of the wulst. Here, we have used autofluorescent flavoprotein imaging and classical anatomical methods to investigate such characteristics of the most posterior map of the multiple retinotopic representations. We found that the visual wulst can be activated by visual stimuli from a large part of the visual field of the contralateral eye. Horizontally, the visual field representation extended from -5° beyond the beak tip up to +125° laterally. Vertically, a small strip from -10° below to about +25° above the horizon activated the visual wulst. Although retinal ganglion cells had a much higher density around the fovea and along a strip extending from the fovea towards the beak tip, these areas were not overrepresented in the wulst map. The wulst area activated from the foveal region of the ipsilateral eye, overlapped substantially with the middle of the three contralaterally activated regions in the visual wulst, and partially with the other two. Visual wulst activity evoked by stimulation of the frontal visual field was stronger with contralateral than with binocular stimulation. This confirms earlier electrophysiological studies indicating an inhibitory influence of the activation of the ipsilateral eye on wulst activity elicited by stimulating the contralateral eye. The lack of a foveal overrepresentation suggests that identification of objects may not be the primary task of the zebra finch visual wulst. Instead, this brain area may be involved in the processing of visual information necessary for spatial orientation.

Audio-Visual Stimulation Improves Visual Search Abilities in Hemianopia due to Childhood Acquired Brain Lesions.

Results obtained in both animal models and hemianopic patients indicate that sound, spatially and temporally coincident with a visual stimulus, can improve visual perception in the blind hemifield, probably due to activation of 'multisensory neurons', mainly located in the superior colliculus. In view of this evidence, a new rehabilitation approach, based on audiovisual stimulation of visual field, has been proposed, and applied in adults with visual field reduction due to unilateral brain lesions. So far, results have been very encouraging, with improvements in visual search abilities. Based on these findings, we have investigated the possibility of inducing long-lasting amelioration also in children with a visual deficit due to acquired brain lesions. Our results suggest that, in the absence of spontaneous recovery, audiovisual training can induce activation of visual responsiveness of the oculomotor system also in children and adolescents with acquired lesions and confirm the putatively important role of the superior colliculus (SC) in this process.

Neural correlates of visual motion processing without awareness in patients with striate cortex and pulvinar lesions.

Patients with striate cortex lesions experience visual perception loss in the contralateral visual field. In few patients, however, stimuli within the blind field can lead to unconscious (blindsight) or even conscious perception when the stimuli are moving (Riddoch syndrome). Using functional magnetic resonance imaging (fMRI), we investigated the neural responses elicited by motion stimulation in the sighted and blind visual fields of eight patients with lesions of the striate cortex. Importantly, repeated testing ensured that none of the patients exhibited blindsight or a Riddoch syndrome. Three patients had additional lesions in the ipsilesional pulvinar. For blind visual field stimulation, great care was given that the moving stimulus was precisely presented within the borders of the scotoma. In six of eight patients, the stimulation within the scotoma elicited hemodynamic activity in area human middle temporal (hMT) while no activity was observed within the ipsilateral lesioned area of the striate cortex. One of the two patients in whom no ipsilesional activity was observed had an extensive lesion including massive subcortical damage. The other patient had an additional focal lesion within the lateral inferior pulvinar. Fiber-tracking based on anatomical and functional markers (hMT and Pulvinar) on individual diffusion tensor imaging (DTI) data from each patient revealed the structural integrity of subcortical pathways in all but the patient with the extensive subcortical lesion. These results provide clear evidence for the robustness of direct subcortical pathways from the pulvinar to area hMT in patients with striate cortex lesions and demonstrate that ipsilesional activity in area hMT is completely independent of conscious perception.

Upper visual field distractors preferentially bias attention to the left

Pseudoneglect is influenced by vertical visual field stimulation, such that attentional biases are stronger for upper space distractors. Leftward biases result from right hemisphere visuospatial processing, and may be accentuated by additional right hemisphere activation during upper space distraction. Three experiments examined potential explanations for this finding. Experiment 1 controlled for perceptual grouping and leftward biases remained stronger in upper space. Experiment 2 used peripheral distractors to eliminate two further potential explanations: centre-of-mass and framing effects. Eye tracking was included to compare overt and covert attention. Findings supported the occurrence of a stronger leftward attentional bias during upper space distraction. Distractors were rarely fixated, suggesting covert attentional mechanisms are preferentially drawn toward upper space distractors. Experiment 3 employed a cueing paradigm that purposefully directed attention away from centre to determine whether pseudoneglect was influenced by overt attentional orienting. Results indicated that when attention was overtly directed away from centre, the strength of pseudoneglect did not differ based on visual field. It is concluded that covert attention toward upper space distractors recruits additional right hemisphere activation, leading existing leftward biases to be accentuated.

Intermixed structure of voxels with different hemispheric characteristics in the fusiform face area

The fusiform face area, a high-level visual area, is pivotal in processing facial information. This area receives inputs from the left and right visual fields unlike the primary visual area, which only receives inputs from its contralateral visual field. Response of the fusiform face area to ipsilateral stimulation depends on the signals crossing over at the corpus callosum. We investigated the distribution of voxel-wise activation to determine whether ipsilateral-dominant voxels exist in the fusiform face area using high spatial resolution functional MRI at 7 T. We further examined the possible functional differences between ipsilateral-dominant and contralateral-dominant voxels. By unilateral visual field stimulation, we detected ipsilateral-dominant voxels in the right fusiform face area. Their distribution was spatially heterogeneous. We tested upright and inverted facial stimulation confined to unilateral visual fields and found that these ipsilateral-dominant voxels had a different functional nature from contralateral-dominant voxels.

Blindsight in children with congenital and acquired cerebral lesions

It has been shown that unconscious visual function can survive lesions to optical radiations and/or primary visual cortex (V1), a phenomenon termed “blindsight”. Studies on animal models (cat and monkey) show that the age when the lesion occurs determines the extent of residual visual capacities. Much less is known about the functional and underlying neuronal repercussions of early cortical damage in humans. We measured sensitivity to several visual tasks in four children with congenital unilateral brain lesions that severely affected optic radiations, and in another group of three children with similar lesions, acquired in childhood. In two of the congenital patients, we measured blood oxygenation level dependent (BOLD) activity in response to stimulation of each visual field quadrants. Results show clear evidence of residual unconscious processing of position, orientation and motion of visual stimuli displayed in the scotoma of congenitally lesioned children, but not in the children with acquired lesions. The calcarine cortical BOLD responses were abnormally elicited by stimulation of the ipsilateral visual field and in the scotoma region, demonstrating a profound neuronal reorganization. In conclusion, our data suggest that congenital lesions can trigger massive reorganization of the visual system to alleviate functional effects of early brain insults.