Biology subjects

Huxlin, K. R.

Publications and source records attributed to Huxlin, K. R..

15 recordsLinked to original sources

bioRxiv2025

Steering in the presence of a gaze-contingent occlusion over a quarter of the visual field

Why do some cortically blind (CB) drivers who are missing vision from a quadrant or hemifield have trouble maintaining a central lane position, while others do not? A recent driving study in virtual reality showed that most patients with right-sided visual field deficits (right CB) perform similarly to controls, while most of those with left CB demonstrated a unique pattern of steering biases (Giguere et al., 2025). In this study, we tested the hypothesis that these biases could result from loss of visual information falling on the blind field. The steering and gaze behavior of 24 subjects with normal vision (mean age: 19.8 years, SD: 1.44) were recorded in a virtual reality steering task while gaze-contingent occluding masks were imposed on a quadrant of their visual field. The central five degrees of vision were spared to mimic the sparing present in most CB patients. Turn direction (left/right), turn radius (two non-constant radii), and occlusion quadrant (one of four quadrants or no occlusion) were randomized between trials. We found that the pattern of steering biases observed in CB drivers were not replicated when visually-healthy drivers were subjected to gaze-contingent masks, and we conclude that it may be a mistake to characterize the effects of cortical blindness on steering behavior as consistent with a simple omission of visual information. This insight has the potential to guide future research on CB adaptation to their visual impairments and possible interventions to improve their steering performance.

animal behavior and cognition↗

bioRxiv2025

The effect of unilateral cortical blindness on lane position and gaze behavior in a virtual reality steering task

Adults with cortically-induced blindness (CB) affecting a quarter to a half of their visual field show greater variability in lane positioning when driving compared to those with intact vision. Because humans rely on visual information from optic flow to control steering, we hypothesized that these lane biases are caused in part by a disruption to motion processing caused by CB. To investigate, we examined the steering behavior of 21 CB drivers (11 left-sided, 10 right-sided visual deficits) and 9 visually intact controls in a naturalistic virtual environment. Participants were instructed to maintain a central lane position while traveling at 19 m/s along a procedurally generated single-lane road. Turn direction (left/right) and turn radius (35m/55m/75m) varied between trials, and the quality of optic flow information was indirectly manipulated by altering the environmental texture density (low/medium/high). Right-sided CB participants maintained a similar average distance from the inner road edge as controls. Those with left-sided CB were less affected by changes in optic flow and turn direction. These differences were not explained by age, time since stroke, sparing of central vision, gaze direction, or saccade rate. Our results suggest that some left-sided CB participants place a lower weighting on optic flow information in the control of steering, possibly as a result of lateralization in the processing of motion. More broadly, our findings show that CB steering and gaze behavior are remarkably preserved despite the presence of visual deficits across large portions of the visual field.

animal behavior and cognition↗

bioRxiv2024

Optic flow density modulates corner-cutting independently of age in a virtual reality steering task

There is a critical need to understand how aging visual systems contribute to age-related increases in vehicle accidents. We investigated the potential contribution of age-related detriments in steering based on optic flow, a source of information known to play a role in navigation control. Seventeen younger adults (mean age: 21.1 years) and thirteen older adults (mean age: 57.3 years) performed a virtual reality steering task. The virtual environment depicted movement at 19 m/s along a winding road. Participants were tasked with maintaining a central lane position while experiencing 8 repetitions of each combination of optic flow density (low, medium, high), turn radius (35, 55, 75 meters), and turn direction (left, right), presented in random order. All participants cut corners, but did so less on turns with rotational flow from distant landmarks and without proximal optic flow. The magnitude of this flow-related effect was independent of age, although older adults cut corners more on all turns. An exploratory gaze analysis revealed no age-related differences in gaze behavior. The lack of age-related differences in steering or gaze behavior as a function of optic flow implies that processing of naturalistic optic flow stimuli when steering may be preserved with age.

neuroscience↗

bioRxiv2023

Transfer of figure-ground segregation learning is facilitated by a cross-modal auditory feature-based attention cue.

This study tested the role of a cross-modal feature based attention (FBA) cue on perceptual learning and spatial transfer. The trained task was figure-ground segregation in the motion domain. The experiment involved a pre-test, ten days of training, and a post-test. Twelve visually intact participants were immersed in a virtual environment and tasked with identifying the location and motion direction of a peripheral 10{whitebullet}aperture of semi-coherently moving dots embedded at randomized locations within whole-field random dot motion. The aperture contained both randomly moving dots and signal dots which had global leftward or rightward motion. To manipulate motion coherence, a 3-up-1-down staircase adjusted the direction range of the signal dots in response to segregation judgments. The dot stimulus was preceded by a 1s white-noise spatialized auditory cue emitted from the fixation point (neutral group), or from an emitter moving in the direction of signal dots at 80{whitebullet}/s in a horizontal arc centered on the fixation point (FBA cue group). Visual feedback indicated the selected and true aperture locations, and correctness of the motion direction judgment. Analysis measured MD discrimination within the aperture as well as segregation ability, both measured in terms of direction range threshold (DRT). At trained locations, MD DRT improved similarly in FBA and neutral groups, and learning was retained when the pre-cue was removed ({Delta}DRT from pretest to posttest: 61{+/-}10{whitebullet}(SD) FBA, 74{+/-}10{whitebullet}neutral), and transferred to untrained locations (41{+/-}10{whitebullet}FBA, 45{+/-}10{whitebullet}neutral). DRT for localization also improved in both groups when pre-cues were removed (49{+/-}10{whitebullet}FBA, 44{+/-}10{whitebullet}neutral), but only the FBA group showed full transfer of learning to untrained locations in the segregation task (32{+/-}10{whitebullet}FBA, 23{+/-}10{whitebullet}neutral). In summary, transfer occurred for both motion direction and segregation tasks, but the segregation transfer required the presence of the cross-modal FBA cue during training.

neuroscience↗

bioRxiv2023

Multisensory perceptual learning in virtual reality may facilitate transfer to untrained locations but is impacted by training procedures.

Visual training improves performance in visually-intact and visually-impaired participants, making it useful as a rehabilitation tool. An interesting question in rehabilitation is whether invocation of multisensory integration could increase training efficacy. To investigate, participants completed a 10-day training experiment wherein they repeatedly performed a 4-way global motion direction discrimination task. On each trial, participants were presented with a 5{degrees} diameter visual global motion stimulus placed in a gaze-contingent manner at 10{degrees} azimuth/elevation. The visual-only group was presented the unimodal visual stimulus. However, for the auditory/visual (AV) group, the visual stimulus was paired with a pulsed white-noise auditory cue moving along in a direction consistent with the horizontal component of the visual motion stimulus. Direction range thresholds (DRT) were computed daily. The motion direction discrimination learning transferred fully in both groups, regardless of the presence of a feature-based attention cue. However, the figure-ground segregation learning only fully transferred to untrained locations with the addition of the feature-based attention cue. These results speak to the multiple levels of processing on which perceptual learning can operate. PACS0000, 1111 2000 MSC0000, 1111

neuroscience↗

bioRxiv2022

Pathway and directional specificity of Hebbian plasticity induction in the cortical visual motion processing network

Cortico-cortical paired associative stimulation (ccPAS), which repeatedly pairs single pulse TMS over two distant brain regions with a specific time interval, is thought to modulate synaptic plasticity. Applied to the motion cortical pathway, ccPAS has been shown to improve motion discrimination when specifically targeting backward projections, stimulating the medio-temporal area (MT) followed by the primary visual cortex (V1). However, there is no direct neuroimaging evidence of the spatial selectivity of the ccPAS effects (i.e., pathway or direction specificity) or detailing the exact nature of the ccPAS effects (i.e., the oscillatory signature, timing...). In this study, we applied ccPAS along the motion discrimination pathway, in the top-down direction (MT-to-V1: "Backward ccPAS") and in the bottom-up direction (V1-to-MT: "Forward ccPAS") in sixteen healthy volunteers and compared changes in visual network activity in response to single pulse TMS over V1 and MT using spectral granger causality (sGC). The sGC results showed common increases in direct V1-to-MT and V1-to-IPS bottom-up inputs in the high Beta/low Gamma band (25-40 Hz) for both ccPAS, probably reflecting task exposure. However, a clear distinction in information transfer occurred in the re-entrant MT-to-V1 signals, which were only modulated by Backward ccPAS. This difference was predictive of the behavioural improvements at the motion discrimination task. Our results support the view of the possibility to specifically enhance re-entrant Alpha oscillatory signals from MT-to-V1 to promote motion discrimination performance through Backward ccPAS. These findings contribute to better understanding visual processing in healthy subjects and how it can be modulated to pave the way to clinical translation in vision handicapped patients. The changes in re-entrant MT-to-V1 inputs could help to provide single-subject prediction scenarios in patients suffering from a visual system stroke, in whom visual recovery might partly rely on the top-down inputs to the spared V1 neurons.

neuroscience↗

bioRxiv2022

Concurrent TMS-fMRI to determine adaptive brain changes to virtual lesions interfering with visual processing

Understanding how focal perturbations lead to large-scale network (re)organization is essential for accurately predicting the behavioral consequences of brain lesions. In this study, we applied a virtual lesion approach by means of short bursts of 10 Hz transcranial magnetic stimulation (TMS) over either early visual areas (EVA) or the medio-temporal area (MT) in healthy participants, while acquiring concurrent functional MRI. TMS delivered during the early stages of motion processing selectively impaired direction discrimination at both sites, while global motion perception remained unaffected. These behavioral effects were accompanied by a common local increase in BOLD activity, but distinct patterns of network reorganization. Perturbation of EVA led to more robust and efficient functional adaptation, suggesting greater resilience to focal disruption. In contrast, behavioral impairments following MT stimulation were associated with a less organized, more random network structure. Together, these findings underscore the potential of TMS-fMRI coupling as a powerful approach for mapping causal disconnectomics--the dynamic relationships between localized neural disruption and widespread functional and behavioral outcomes providing a better understanding of lesion-induced brain changes in neurological disorders such as stroke. HighlightsO_LITMS-induced perturbation of the early visual areas (EVA) or the mediotemporal area (MT) area selectively impairs motion direction discrimination. C_LIO_LIThe TMS perturbation is associated with a context-dependent local up-scaling of BOLD activity in both areas. C_LIO_LIThe two visual areas display distinct topological networks adaptation in response to TMS, reflecting different levels of network resilience to a focal lesion. C_LIO_LITMS-fMRI coupling can be used to assess causal disconnectomics and to precisely map how a local perturbation propagates to large-scale behavioural deficits. C_LI

neuroscience↗

bioRxiv2021

Perceptual restoration fails to recover unconscious processing for smooth eye movements after occipital stroke

The visual pathways that guide actions do not necessarily mediate conscious perception. Patients with primary visual cortex (V1) damage lose conscious perception but often retain unconscious abilities (e.g. blindsight). Here, we asked if saccade accuracy and post-saccadic following responses (PFRs) that automatically track target motion upon saccade landing are retained when conscious perception is lost. We contrasted these behaviors in the blind and intact-fields of 11 chronic V1-stroke patients, and in 8 visually-intact controls. Saccade accuracy was relatively normal in all cases. Stroke patients also had normal PFR in their intact-fields, but no PFR in their blind-fields. Thus, V1 damage did not spare the unconscious visual processing necessary for automatic, post-saccadic smooth eye movements. Importantly, visual training that recovered motion perception in the blind-field did not restore the PFR, suggesting a clear dissociation between pathways mediating perceptual restoration and automatic actions in the V1-damaged visual system.

neuroscience↗

bioRxiv2020

Bifocal tACS Enhances Visual Motion Discrimination by Modulating Phase Amplitude Coupling Between V1 and V5 Regions

Visual motion discrimination involves reciprocal interactions in the alpha band between the primary visual cortex (V1) and the mediotemporal area (V5/MT). We investigated whether modulating alpha phase synchronization using individualized multisite transcranial alternating current stimulation (tACS) over V5 and V1 regions would improve motion discrimination. We tested 3 groups of healthy subjects: 1) an individualized In-Phase V1alpha-V5alpha tACS (0{degrees} lag) group, 2) an individualized Anti-Phase V1alpha-V5alpha tACS (180{degrees} lag) group and 3) a sham tACS group. Motion discrimination and EEG activity were compared before, during and after tACS. Performance significantly improved in the Anti-Phase group compared to that in the In-Phase group at 10 and 30 minutes after stimulation. This result could be explained by changes in bottom-up alpha-V1 gamma-V5 phase-amplitude coupling. Thus, Anti-Phase V1alpha-V5alpha tACS might impose an optimal phase lag between stimulation sites due to the inherent speed of wave propagation, hereby supporting optimized neuronal communication. IMPACT STATEMENTO_LIAlpha multisite (V1 and V5) tACS influences global motion discrimination and integration C_LIO_LIPhase-amplitude coupling is associated with visual performance C_LIO_LIMultisite Anti-Phase stimulation of strategic visual areas (V1 and V5) is associated with connectivity changes in the visual cortex and thus, associated with changes in direction acuity C_LI

neuroscience↗

bioRxiv2020

How scars shape the neural landscape: key molecular mediators of TGF-β1s anti-neuritogenic effects

Following injury to the peripheral and central nervous systems, tissue levels of transforming growth factor (TGF)-{beta}1 often increase, which is key for wound healing and scarring. However, active wound regions and scars appear to inhibit process outgrowth by regenerating neurons. We recently showed that corneal wound myofibroblasts block corneal nerve regeneration in vivo, and sensory neurite outgrowth in vitro in a manner that relies critically on TGF-{beta}1. In turn, delayed, abnormal re-innervation contributes to long-term sensory dysfunctions of the ocular surface. Here, we exposed morphologically and biochemically-differentiated sensory neurons from the ND7/23 cell line to TGF-{beta}1 to identify the intracellular signals regulating these anti-neuritogenic effects, contrasting them with those of Semaphorin(Sema)3A, a known inhibitor of neurite outgrowth. Neuronal morphology was quantified using phase-contrast imaging. Western blotting and specific inhibitors were then used to identify key molecular mediators. Differentiated ND7/23 cells expressed neuron-specific markers, including those involved in neurite extension and polarization. TGF-{beta}1 increased phosphorylation of collapsin response mediator protein-2 (CRMP2), a molecule that is key for neurite extension. We now show that both glycogen synthase kinase (GSK)-3{beta} and Smad3 modulate phosphorylation of CRMP2 after treatment with TGF-{beta}1. GSK-3{beta} appeared to exert a particularly strong effect, which could be explained by its ability to phosphorylate not only CRMP2, but also Smad3. In conclusion, TGF-{beta}1s inhibition of neurite outgrowth in sensory neurons appears to be regulated through a highly-conserved signaling pathway, which involves the GSK-3{beta}/CRMP-2 loop via both canonical and non-canonical mechanisms. It is hoped that by defining the signaling pathways that control neurite outgrowth in wound environments, it will become possible to identify optimal molecular targets to promote re-innervation following injury.

neuroscience↗

bioRxiv2020

Online Transcranial Random Noise stimulation improves perception at high levels of visual white noise

Transcranial random noise stimulation (tRNS), a relatively recent addition to the field of non-invasive, electrical brain stimulation, has been shown to improve perceptual and cognitive functions across a wide variety of tasks. However, the underlying mechanisms of visual improvements caused by tRNS remain unclear. To study this question, we employed a well-established, equivalent-noise approach, which measures perceptual performance at various levels of external noise and is formalized by the Perceptual Template Model (PTM). This approach has been used extensively to infer the underlying mechanisms behind changes in visual processing, including those from perceptual training, adaptation and attention. Here, we used tRNS during an orientation discrimination task in the presence of increasing quantities of external visual white noise and fit the PTM to gain insights into the effects of tRNS on visual processing. Our results show that tRNS improves visual processing when stimulation is applied during task performance, but only at high levels of external visual white noise--a signature of improved external noise filtering. There were no significant effects of tRNS on task performance after the stimulation period. Of interest, the reported effects of tRNS on visual processing mimic those previously reported for endogenous spatial attention, offering a potential area of investigation for future work.

neuroscience↗

bioRxiv2020

Changes in perilesional V1 underlie training-induced recovery in cortically-blind patients

Damage to the primary visual cortex (V1) causes profound, homonymous visual-field loss termed cortical blindness (CB). Though long considered intractable, multiple studies now show that perceptual training can recover visual functions in chronic CB. A popular hypothesis is that training recruits intact extrageniculostriate pathways. Alternatively, training may induce plastic changes within spared regions of the damaged V1. Here, we linked changes in luminance detection sensitivity with retinotopic fMRI activity in eleven chronic CB patients, before and after extensive visual discrimination training. Our results show that the strength of spared V1 activity representing perimetrically blind-field locations before training predicts the amount of training-induced recovery of luminance detection sensitivity. Additionally, training caused an enlargement of population receptive fields in perilesional V1 cortex, which increased blind-field coverage. These findings uncover fundamental changes in perilesional V1 cortex underlying training-induced restoration of conscious luminance detection sensitivity in cortically-blind patients.

neuroscience↗

bioRxiv2020

Functional reorganization of visual processing following long-term adaptation to optical defects

How we see is fundamentally limited by the eyes optics, which determine retinal image quality and constrain neural processing. Elucidating how long-term exposure to optical defects alters visual processing is vital for understanding the human brains capacity for and limits of sensory plasticity. Using adaptive optics to bypass the eyes optical aberrations, we assessed changes in visual processing in neurotypically-developed adults with keratoconus (KC)--a corneal disease causing severe optical aberrations during adulthood that cannot be fully corrected using conventional methods. As a result, KC patients are chronically exposed to degraded retinal images in their everyday life, making them an ideal model to understand how prolonged exposure to poor optical quality alters visual processing. Here, we show that when tested under similar fully-corrected optical conditions as neurotypical observers, KC patients exhibited altered contrast sensitivity, with impaired sensitivity for fine spatial details and better sensitivity for coarse spatial details. Both gains and losses in contrast sensitivity were more pronounced in patients with poorer habitual optical quality. Moreover, using an equivalent noise paradigm and a computational model of visual processing, we show that these alterations in visual processing are mediated by changes in signal enhancement of spatial frequency selective mechanisms. The present findings uncover fundamental properties of neural compensation mechanisms in response to long-term exposure to optical defects, which alter sensory processing and limit the benefits of improved optics. The outcome is a large-scale functional reorganization favoring the processing of sensory information less affected by the eyes optics. Significance statementThe eyes optics represent an intrinsic limit to human visual perception, determining the quality of retinal images. Neural adaptation optimizes the brains limited sensory processing capacity to the structure of the degraded retinal inputs, providing an exceptional quality of vision given these optical limitations. Here, we show that prolonged exposure to poor optical quality results in a functional reorganization of visual processing that favors sensory information less affected by the eyes optics. The present study helps elucidate how optical factors shape the way the brain processes visual information. Notably, the resulting adaptive neural plasticity limits the immediate perceptual benefits of optical interventions, a factor that must be taken into consideration when treating the increasing human population affected by optical defects.

neuroscience↗

bioRxiv2019

Time is vision: functional preservation and enhanced capacity for recovery in subacute occipital stroke

Stroke damage to the primary visual cortex (V1) causes a loss of vision known as hemianopia or cortically-induced blindness (CB). While early, spontaneous, perimetric improvements can occur, by 6 months post-stroke, the deficit is considered chronic and permanent. Despite evidence from sensorimotor stroke showing that early injury responses heighten neuroplastic potential, to date, rehabilitation research has focused only on chronic CB patients. Consequently, little is known about the functional properties of subacute, post-stroke visual systems, and whether they can be harnessed to enhance visual recovery. Here, for the first time, we show that conscious visual discrimination abilities are partially preserved inside subacute, perimetrically-defined blind fields, disappearing by 6 months post-stroke. Complementing this discovery, we show that global motion discrimination training initiated subacutely leads to comparable magnitude of recovery as that initiated in chronic CB. However, it does so 6 times faster, generalizes to deeper, untrained regions of the blind field, and to other [untrained] aspects of motion perception, preventing their degradation upon reaching the chronic period. Untrained subacutes exhibited only spontaneous improvements in perimetry - spontaneous recovery of motion discriminations was never observed. Thus, in CB, the early post-stroke period appears characterized by gradual - rather than sudden - loss of visual processing. Subacute training stops this degradation, and is dramatically more efficient at eliciting recovery than identical training in the chronic period. Finally, spontaneous improvements in subacutes appear restricted to luminance detection, whereas recovering discrimination abilities requires deliberate training. Simply stated, after an occipital stroke, "time is VISION". One Sentence SummaryThe first 3 months after an occipital stroke are characterized by a gradual - not sudden - loss of visual perceptual abilities and increased rehabilitative potential if visual discrimination training is administered in the blind field.

neuroscience↗

bioRxiv2017

Altered sensitivity to motion of area MT neurons following long-term V1 lesions

The middle temporal area (MT) receives its main afferents from the striate cortex (V1). However, MT also receives direct thalamic projections, which have been hypothesized to play a crucial role in residual vision after V1 lesions. MT neurons continue to respond shortly after V1 lesions, but human clinical work has shown that lesion effects can take up to six months to stabilize, making it important to understand MT responses after long-term deprivation of V1 inputs. We recorded neuronal responses in MT to moving dot stimuli in adult marmoset monkeys, 7-11 months after unilateral V1 lesions. Fewer MT neurons were direction selective, including neurons whose locations corresponded to the intact parts of V1. Firing rates were higher and more variable, and increased with motion strength regardless of direction. These properties could be re-created by a network model with imbalanced inhibition and excitation, providing the first insights into functional implications of long-term plasticity in MT following V1 lesions.

neuroscience↗