Biology subjects

Rokers, B.

Publications and source records attributed to Rokers, B..

9 recordsLinked to original sources

bioRxiv2024

Gray matter abnormalities in sight deprivation and sight restoration

Blindness provides a unique model for investigating brain plasticity in response to sensory deprivation. While structural changes in both gray and white matter have been widely documented, particularly in cases of early or congenital visual deprivation, gray matter studies have traditionally focused on cortical thickness, often finding cortical thickening in posterior regions. However, other aspects of gray matter integrity, such as cortical myelin content, remain underexplored. In this study, we examined the effects of visual deprivation on cortical structure in a cohort of congenitally blind individuals who received eye surgery during adolescence, expanding beyond conventional measures to include cortical thickness, curvature, and T1-weighted signal intensity. This multi-faceted approach offers a more comprehensive view of cortical adaptations to congenital sensory deprivation. While blindness offers valuable insights into sensory-driven brain plasticity, an intriguing and unresolved question is whether structural plasticity reverses after sight restoration, enabling typical visual processing circuits to develop despite the initial period of deprivation. To address this, we assessed the effect of sight-recovering eye surgery on gray matter changes. Critically, individuals in this cohort received surgery after the closure of the sensitive period for visual development. We did not find evidence of gray matter changes after surgery. However, in a previous study conducted on the same cohort, we reported that notable plasticity in white matter emerged in this same population. These results suggest that white matter alterations, rather than gray matter changes, may potentially serve as a biomarker of structural plasticity following sight restoration, even beyond the sensitive developmental window.

neuroscience↗

bioRxiv2024

Characterizing dynamic functional connectivity in congenitally blind people using Hidden Markov Models

How sensory experience shapes the organization of the human brain connectome remains a central question in neuroscience. Previous studies of congenital blindness have primarily relied on stationary functional connectivity, potentially overlooking how sensory deprivation affects the temporal reconfiguration of large-scale brain networks. Here, we investigated dynamic functional connectivity in blindness by comparing resting-state fMRI data from sighted (n = 50) and early blind individuals (n = 33) using a data-driven hidden Markov model approach. Early blind individuals exhibited increased fractional occupancy of two brain states characterized by bilateral somatomotor and left-lateralized occipito-frontal networks, whereas sighted participants more frequently occupied a state dominated by default mode and ventral attention networks. Connectivity states preferentially expressed by sighted participants showed reduced visual-somatomotor coupling in blind individuals, while states more frequently visited by early blind participants exhibited enhanced connectivity within the visual network and between occipital, fusiform, and prefrontal regions. Critically, the hyperconnectivity in blindness was largely explained by altered state occupancy, indicating that temporal dynamics, rather than connectivity patterns per se, drive reorganization. Beyond temporal dynamics, visual deprivation altered the spatial organization of functional gradients derived from model-based, state-specific connectivity: occipital regions shifted closer to transmodal networks, while the overall low-dimensional geometry of latent states remained largely preserved. This suggests that early visual deprivation selectively reshapes the temporal expression and functional embedding of brain states without altering the core scaffold of large-scale dynamics. Together, these findings demonstrate that blindness reshapes both the temporal and spatial structure of large-scale brain networks, highlighting the chronnectome as a critical substrate of experience-dependent plasticity. Significance StatementBlindness provides a unique opportunity to understand how the human brain reorganizes in the absence of typical sensory experience. Previous studies have relied on stationary functional connectivity, overlooking the role of temporal network dynamics. Using a data-driven Hidden Markov Model approach applied to resting-state fMRI, we show that early visual deprivation primarily alters the temporal dynamics of brain states. Crucially, the hyperconnectivity classically observed in early blind individuals emerges from changes in state occupancy rather than intrinsic alterations of connectivity patterns. Beyond temporal effects, we also demonstrate that visual deprivation reshapes functional gradients, with occipital regions shifting toward transmodal systems. Together, these findings reveal the chronnectome as a key mechanism of experience-dependent plasticity, while preserving a robust large-scale organizational scaffold.

neuroscience↗

bioRxiv2024

Functional localization of visual motion area FST in humans

The fundus of the superior temporal sulcus (FST) in macaques is implicated in the processing of complex motion signals, yet a human homolog remains elusive. Here we considered potential localizers and evaluated their effectiveness in delineating putative FST (pFST), from hMT and MST, two nearby motion-sensitive areas in humans. Nine healthy participants underwent scanning sessions with 2D and 3D motion localizers, as well as population receptive field (pRF) mapping. We observed consistent anterior and inferior activation relative to hMT and MST in response to stimuli that contained coherent 3D, but not 2D, motion. Motion opponency and myelination measures further validated the functional and structural distinction between pFST and hMT/MST. At the same time, standard pRF mapping techniques that reveal the visual field organization of hMT/MST proved suboptimal for delineating pFST. Our findings provide a robust framework for localizing pFST in humans, and underscore its distinct functional role in motion processing.

neuroscience↗

bioRxiv2022

Identifying cortical areas that underlie the transformation from retinal to world motion signals

Accurate motion perception requires that the visual system integrate the retinal motion signals received by the two eyes into a single representation of 3D (i.e., world) motion. However, most experimental paradigms limit the motion stimuli to the fronto-parallel plane (i.e., 2D motion) and are thus unable to dissociate retinal and world motion signals. Here, we used stereoscopic displays to present separate motion signals to the two eyes and examined their representation in visual cortex using fMRI. Specifically, we presented random-dot motion stimuli that produced percepts of various 3D motion trajectories. We also presented control stimuli that contained the same retinal motion energy in the two eyes but were inconsistent with any 3D motion trajectory. We decoded the stimuli from BOLD activity using a probabilistic decoding algorithm. We found that 3D motion direction can be reliably decoded in three major clusters in the human visual system. In early visual cortex (V1-V3), we found no significant difference in decoding performance between the 3D motion and control stimuli, suggesting that these areas represent retinal motion rather than world motion signals. In voxels in and surrounding hMT and IPS0 however, decoding performance was consistently superior for 3D motion compared to control stimuli. Our results reveal the parts of the visual processing hierarchy that are critical for the transformation of retinal into world motion signals and suggest a role for IPS0 in the representation of 3D motion signals, in addition to its sensitivity to 3D object structure and static depth.

neuroscience↗

bioRxiv2022

Task feedback suggests a post-perceptual locus of serial dependence

Decisions across a range of perceptual tasks are biased toward past stimuli. Such serial dependence is thought to be an adaptive low-level mechanism that promotes perceptual stability across time. However, recent studies suggest post-perceptual mechanisms may also contribute to serially-biased responses, calling into question a single locus of serial dependence and the nature of integration of past and present sensory inputs. We measured serial dependence in the context of a 3D motion perception task where uncertainty in the sensory information varied substantially from trial to trial. We found that serial dependence varied with stimulus properties that impact sensory uncertainty on the current trial. Reduced stimulus contrast was associated with an increased bias toward the previous trials stimulus direction. Critically, performance feedback, which reduced sensory uncertainty, abolished serial dependence. These results provide clear evidence for a post-perceptual locus of serial dependence in 3D motion perception and support the role of serial dependence as a response strategy in the face of substantial sensory uncertainty.

neuroscience↗

bioRxiv2019

Perceptual metacognition of human faces is causally supported by function of the lateral prefrontal cortex

Metacognitive visual awareness--the ability to know that one is having a particular visual experience--is thought to optimally guide behavior and help us accurately navigate our complex social environments. Yet the neural underpinnings of visual metacognition continue to be the subject of vigorous debate: While prior work identified correlations between perceptual metacognitive ability and the structure and function of lateral prefrontal cortex (LPFC), evidence for a causal role of this region in promoting metacognition is controversial--in fact, some question whether the prefrontal cortex plays any role in supporting conscious visual experiences. Moreover, whether LPFC function promotes metacognitive awareness of perceptual and emotional features of complex, yet ubiquitous socio-emotional face stimuli is unknown. Using model-based analyses following a causal intervention to LPFC in humans, we demonstrate that LPFC promotes metacognitive awareness of the orientation of emotional faces--although not of their emotional expressions. Effects were specific to metacognition, as LPFC perturbation did not alter stimulus discrimination performance. Collectively, these data support the causal involvement of the prefrontal cortex in metacognitive awareness, and indicate that the role of LPFC function in metacognition encompasses perceptual experiences of naturalistic social stimuli.

neuroscience↗

bioRxiv2018

Variability in Sensory Sensitivity Predicts Motion Sickness in Virtual Reality

Severity of motion sickness varies across individuals. While some experience immediate symptoms, others seem relatively immune. We explored a potential explanation for such individual variability based on cue conflict theory. According to cue conflict theory, sensory signals that lead to mutually incompatible perceptual interpretations will produce physical discomfort. A direct consequence of such theory is that individuals with greater sensitivity to visual (or vestibular) sensory cues should show greater susceptibility, because they would be more likely to detect a conflict. Using virtual reality (VR), we first assessed individual sensitivity to a number of visual cues and subsequently induced moderate levels of motion sickness using stereoscopic movies presented in the VR headset. We found that an observers sensitivity to motion parallax cues predicted severity of motion sickness symptoms. We also evaluated evidence for another reported source of variability in motion sickness severity in VR, namely sex, but found little support. We speculate that previously-reported sex differences might have been due to poor personalization of VR displays, which default to male settings and introduce cue conflicts for the majority of females. Our results identify a sensory sensitivity-based predictor of motion sickness, which can be used to personalize VR experiences and mitigate discomfort.

neuroscience↗

bioRxiv2018

Linking Retinal, Neural, and Perceptual Measures of Glaucoma with Diffusion Magnetic Resonance Imaging (dMRI)

AbstractO_ST_ABSPurposeC_ST_ABSTo link optic nerve (ON) structural integrity to clinical markers of glaucoma using advanced, semi-automated diffusion weighted imaging (DWI) tractography methods in human glaucoma patients.\n\nMethodsWe characterized optic neuropathy in patients with unilateral advanced-stage glaucoma (n = 6) using probabilistic DWI tractography and compared their results to those in healthy controls (n=6).\n\nResultsWe successfully identified the ONs of glaucoma patients based on DWI in all patients and confirmed that the degree of reduced structural integrity of the ONs determined using DWI correlated with clinical markers of glaucoma severity. Specifically, we found reduced fractional anisotropy (FA), a measure of structural integrity, in the ONs of eyes with advanced, as compared to mild, glaucoma (F(1,10) = 55.474, p < 0.0001). Furthermore, by comparing the ratios of ON FA in glaucoma patients to those of healthy controls (n = 6), we determined that this difference was beyond that expected from normal anatomical variation (F(1,9) = 20.276, p < 0. 005). Finally, we linked the DWI-measures of neural integrity to standard clinical glaucoma measures. ON vertical cup-to-disc ratio (vCD) predicted ON FA (F(1,10) = 11.061, p < 0.01, R2 = 0.66), retinal nerve fiber layer thickness (RNFL) predicted ON FA (F(1,10) = 11.477, p < 0.01, R2 = 0.63) and ON FA predicted perceptual deficits (visual field index [VFI]) (F(1,10) = 15.308, p < 0.005, R2 = 0.52).\n\nConclusionWe provide semi-automated methods to detect glaucoma-related structural changes using DWI and confirm that they correlate with clinical measures of glaucoma.

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bioRxiv2017

Systematic misperceptions of 3D motion explained by Bayesian inference

People make surprising but reliable perceptual errors. Here, we provide a unified explanation for errors in the perception of three-dimensional (3D) motion. To do so, we characterized the retinal motion signals produced by objects moving with arbitrary trajectories through arbitrary locations in 3D. Next, we developed a Bayesian model, treating 3D motion perception as optimal inference given sensory noise and the geometry of 3D viewing. The model predicts a wide array of systematic perceptual errors, that depend on stimulus distance, contrast, and eccentricity. We then used a virtual reality (VR) headset as well as a standard 3D display to test these predictions in both traditional psychophysical and more naturalistic settings. We found evidence that people make many of the predicted errors, including a lateral bias in the perception of motion trajectories, a dependency of this bias on stimulus contrast, viewing distance, and eccentricity, and a surprising tendency to misreport approaching motion as receding and vice versa. In sum, we developed a quantitative model that provides a parsimonious account for a range of systematic misperceptions of motion in naturalistic environments.

neuroscience↗