Stimulus- and Neural-Referred Visual Receptive Field Properties following Hemispherectomy: A Case Study Revisited

Abstract

Damage to the visual system can result in (a partial) loss of vision, in response to which the visual system may functionally reorganize. Yet the timing, extent, and conditions under which this occurs are not well understood. Hence, studies in individuals with diverse congenital and acquired conditions and using various methods are needed to better understand this. In the present study, we examined the visual system of a young girl who received a hemispherectomy at the age of three and who consequently suffered from hemianopia. We did so by evaluating the corticocortical and retinocortical projections in the visual system of her remaining hemisphere. For the examination of these aspects, we analyzed the characteristics of the connective fields (“neural-referred” receptive fields) based on both resting-state (RS) and retinotopy data. The evaluation of RS data, reflecting brain activity independent from visual stimulation, is of particular interest as it is not biased by the patient’s atypical visual percept. We found that, primarily when the patient was at rest, the connective fields between V1 and both early and late visual areas were larger than normal. These abnormally large connective fields could be a sign either of functional reorganization or of unmasked suppressive feedback signals that are normally masked by interhemispheric signals. Furthermore, we confirmed our previous finding of abnormal retinocortical or “stimulus-referred” projections in both early and late visual areas. More specifically, we found an enlarged foveal representation and smaller population receptive fields. These differences could also be a sign of functional reorganization or rather a reflection of the interruption visual information that travels, via the remainder of the visual pathway, from the retina to the visual cortex. To conclude, while we do find indications for relatively subtle changes in visual field map properties, we found no evidence of large-scale reorganization—even though the patient could have benefitted from this. Our work suggests that at a later developmental stage, large-scale reorganization of the visual system no longer occurs, while small-scale properties may still change to facilitate adaptive processing and viewing strategies.

Convergence Along the Visual Hierarchy Is Altered in Posterior Cortical Atrophy

“…As opposed to visual stimulus-based cortical mapping, the control subjects’ connective field modeling in resting-state conditions indicated diverging patterns, suggesting cumulative top-down effects in the absence of visual stimuli. This finding corresponds with what was suggested by Halbertsma et al 8 Unlike visual stimulation conditions, the spatial convergence magnitude of the resting-state connective field does not change along the hierarchy. This was already found by Gravel et al, 10 who assessed V1 to V3 resting-state connective fields, but in this study we expanded this notion to high-order visual areas, as well.…”

“… 19 Thus, connective fields that were modeled with visual stimulation were considered to be less sensitive to feedback influences. 8 …”

“… 5 – 7 Another approach is the connective field technique, which assesses how voxels in a target area (e.g., V2) are explained by a circular Gaussian that is folded to follow the cortical surface. 8 – 10 These modeling approaches are usually based on functional magnetic resonance imaging (fMRI) data that have been acquired under visual stimuli conditions. Another way to study connectivity is by examining spontaneous neural activity, during resting state conditions (RS-fMRI).…”

Visual field reconstruction using fMRI-based techniques

“…Note that the discarded voxels correspond to the ones where the MP did not converge, which is most likely due to noisy measured signals. This threshold is equivalent to the one applied in standard analysis of the pRF modelling (section 2.4.4.1, 27,28 ). Figure 2 represents a scheme of the steps underlying the VF reconstruction using micro-probing.…”

Foveal pRF properties in the visual cortex depend on the extent of stimulated visual field

“…Over the last decade, a model based fMRI approach termed population receptive field mapping , has been widely used in investigating visual cortex functioning and contributed to our understanding of pRF characteristics of the visual cortex in healthy vision (Harvey and Dumoulin, 2011;Lee et al, 2013;Wandell and Winawer, 2015;Zeidman et al, 2018;Zuiderbaan et al, 2012). Furthermore, pRF modeling allowed us to quantitatively assess potential alterations of pRF characteristics in the visual cortex in the face of retinal lesions (Barton and Brewer, 2015;Baseler et al, 2011), developmental disorders Carvalho et al, 2019;Hoffmann et al, 2012;Hoffmann and Dumoulin, 2015) and trauma (Haak et al, 2014;Halbertsma et al, 2019;Papanikolaou et al, 2014). While alterations could be interpreted as evidence for potential cortical remapping and as an explanation for changes in fMRI responses following visual field defects (Baker et al, 2008;Dilks et al, 2009;Ferreira et al, 2017;Zhou et al, 2017), there is growing evidence for more conservative views on the nature and extent of adult visual cortex plasticity (Masuda et al, 2010(Masuda et al, , 2008Wandell and Smirnakis, 2009).…”