Biology subjects

Kanowski, M.

Publications and source records attributed to Kanowski, M..

3 recordsLinked to original sources

bioRxiv2020

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

Previous studies demonstrated that alterations in functional MRI derived receptive field (pRF) properties in cortical projection zones of retinal lesions can erroneously be mistaken for cortical large-scale reorganization in response to visual system pathologies. We tested, whether such confounds are also evident in the normal cortical projection zone of the fovea for simulated peripheral visual field defects. We applied fMRI-based visual field mapping of the central visual field at 3 Tesla in eight controls to compare the pRF properties of the central visual field of a reference condition (stimulus radius: 14{degrees}) and two conditions with simulated peripheral visual field defect, i.e., with a peripheral gray mask, stimulating only the central 7{degrees} or 4{degrees} radius. We quantified, for the cortical representation of the actually stimulated visual field, the changes in the position and size of the pRFs associated with reduced peripheral stimulation using conventional and advanced pRF modeling. We found foveal pRF-positions ([≤]3{degrees}) to be significantly shifted towards the periphery (p<0.05, corrected). These pRF-shifts were largest for the 4{degrees} condition [visual area (mean eccentricity shift): V1 (0.9{degrees}), V2 (0.9{degrees}), V3 (1.0{degrees})], but also evident for the 7{degrees} condition [V1 (0.5{degrees}), V2 (0.5{degrees}), V3 (0.9{degrees})]. Further, an overall enlargement of pRF-sizes was observed. These findings indicate the dependence of foveal pRF parameters on the spatial extent of the stimulated visual field. Consequently, our results imply that, previously reported similar findings in patients with actual peripheral scotomas need to be interpreted with caution and indicate the need for adequate control conditions in investigations of visual cortex reorganization. HighlightsO_LIFoveal pRF properties change in controls with restricted peripheral stimulation C_LIO_LIpRFs shift in position and enlarge in size for reduced stimulation extent C_LIO_LIAlterations in pRF characteristics in patients should be interpreted with caution C_LIO_LIAdequate control conditions needed in investigations of visual cortex plasticity C_LI

neuroscience↗

bioRxiv2019

Population receptive field and connectivity properties of the early visual cortex in human albinism

In albinism, the pathological decussation of the temporal retinal afferents at the optic chiasm leads to superimposed representations of opposing hemifields in the visual cortex. Here, we assessed the equivalence of the two representations and the cortico-cortical connectivity of the early visual areas. Applying fMRI-based population receptive field (pRF)-mapping (both hemifield and bilateral mapping) and connective field (CF)-modeling, we investigated the early visual cortex in 6 albinotic participants and 4 controls. In albinism, superimposed retinotopic representations of the contra- and ipsilateral visual hemifield were observed on the hemisphere contralateral to the stimulated eye. This was confirmed by the observation of bilateral pRFs during bilateral mapping. Hemifield mapping revealed similar pRF-sizes for both hemifield representations throughout V1 to V3. The typical increase of V1-sampling extent for V3 compared to V2 was not found for the albinotic participants. The similarity of the pRF-sizes for opposing visual hemifield representations highlights the equivalence of the two maps in the early visual cortex. The altered V1-sampling extent in V3 indicates the adaptation of cortico-cortical connections to the abnormal input of the visual cortex. These findings thus suggest that conservative developmental mechanisms are complemented by alterations of the extrastriate cortico-cortical connectivity.\n\nHighlightsO_LIpRF mapping confirms cortical overlay of opposing visual hemifields in albinism.\nC_LIO_LIEquivalent information processing of both hemifields is indicated by similar pRF sizes.\nC_LIO_LICF modeling indicates changes to the cortico-cortical connections at the level of V3.\nC_LI

neuroscience↗

bioRxiv2018

The effect of acquisition resolution on orientation decoding from V1: comparison of 3T and 7T

Previously published results indicate that the accuracy of decoding visual orientation from 7T fMRI data of V1 peaks at spatial acquisition resolutions that are routinely accessible with more conventional 3T scanners. This study directly compares the decoding performance between a 3T and a 7T dataset that were acquired using the same stimulation paradigm by applying an identical analysis procedure. The results indicate that decoding models built on 3T data are comparatively impaired. Moreover, we found no evidence for a strong coupling of BOLD signal change magnitude or temporal signal to noise ratio (tSNR) with decoding performance. Direct enhancement of tSNR via multiband fMRI acquisition at the same resolution did not translate into improved decoding performance. Additional voxel selection can boost 3T decoding performance to the 7T level only at a 3mm acquisition resolution. In both datasets the BOLD signal available for orientation decoding is spatially broadband, but, consistent with the size of the BOLD point-spread-function, decoding models at 3T utilize spatially coarser image components.

neuroscience↗