Biology subjects

Fracasso, A.

Publications and source records attributed to Fracasso, A..

17 recordsLinked to original sources

bioRxiv2026

No Evidence of tACS-Primed Enhancement of Alpha Neurofeedback

Neurofeedback shows promise as a clinical intervention, but its effectiveness is hindered by variability of response across individuals. One factor influencing neurofeedback success may be endogenous brain states, particularly the baseline power within target frequency bands. Transcranial alternating current stimulation (tACS) provides a potential mechanism to modulate these baseline frequency bands. This study explored whether tACS could effectively enhance participants' ability to gain neurofeedback control by increasing lateralised posterior alpha activity prior to engagement in a covert spatial attention-based neurofeedback task. Participants completed three counterbalanced sessions: 1) alpha tACS and active neurofeedback, 2) alpha tACS and sham neurofeedback, 3) gamma (40Hz) tACS and active neurofeedback. Neurofeedback performance was assessed via lateralised posterior alpha power shifts and Posner task reaction times. We identified no difference in reaction times or lateralised alpha power shifts across conditions. While participants reliably demonstrated lateralised posterior alpha patterns, consistent with the covert spatial attention neurofeedback protocol, no advantage of active neurofeedback over sham was observed. The lack of significant effects underscores the need for further rigorous tACS studies to identify the parameters essential for successful neural entrainment, and to evaluate its potential in enhancing neurofeedback efficacy.

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bioRxiv2026

Mapping memory-guided saccade population receptive fields reveals principles of cortical organization along the human intraparietal sulcus

The intraparietal sulcus is a central hub for motor planning and sensorimotor integration. Its responses are known to support coordinate transformations across reference frames and modalities--for example, eye-position gain fields that convert retinotopic, fovea-centred signals into head-centred representations. In the oculomotor domain, the human intraparietal sulcus is sensitive to eye-movement planning and has been extensively studied using memory-guided saccade paradigms. These classic approaches have revealed topographic organization and contralateral sensitivity for preferred direction in saccade planning and execution. However, such designs provide detailed information about preferred direction; they do not probe tuning width: how narrowly or broadly a given cortical location responds around its preferred direction. At present, it remains unclear whether and how tuning width is organized along the human intraparietal sulcus. Critically, neurophysiological studies in non-human primates do not offer systematic and extensive measurements of tuning width. Moreover, the relationship between tuning width and preferred direction at the population level in human intraparietal cortex is unknown. Here, we address these questions using a forward-modelling approach combined with high-field (7-Tesla) functional MRI. We observe contralateral preference for preferred direction in saccade planning and execution, as well as a novel large-scale organization of preferred saccade tuning width, in vivo, in humans. Highlightssaccade planning and execution tuning width is arranged topographically along human early visual cortex and human intraparietal sulcus; specificity of voxel-level saccade planning and execution decreases along the visual hierarchy; specificity of population-level saccade planning and execution increases along the visual hierarchy; forward modelling applied to memory-guided saccade paradigm outperforms the standard phase-encoding approach;

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bioRxiv2025

Sustained dynamics of saccadic inhibition and adaptive oculomotor responses during continuous exploration

In natural environments, stimuli often recur across time and space, requiring the visual system to remain sensitive to novelty while managing predictability. A central question in systems neuroscience is how motor systems adapt to repeated sensory events without compromising responsiveness. We investigated this adaptive capacity using saccadic inhibition (SI)--a reflexive suppression of eye movements triggered by sudden visual transients--as a probe of oculomotor dynamics during naturalistic viewing. Human participants (N = 21) freely explored visual arrays while brief gaze-contingent flashes appeared five times at random intervals, either foveally or parafoveally. SI reliably occurred [~]120 ms post-flash across repetitions and locations, indicating robust sensory-driven inhibition. However, the rebound phase--reflecting saccade reprogramming--showed a progressive decline. In a second experiment (N = 19), only the first or the fifth flash was visible on each trial. In this case, neither inhibition nor rebound was altered, suggesting that the rebound decline is driven by repeated sensory stimulation rather than exploration time. This dissociation reveals selective habituation of motor re-engagement mechanisms, while reflexive inhibitory gating remains stable. We propose that inhibition is mediated by circuitry that transiently suppresses saccade initiation and resists habituation. By contrast, the weakening rebound reflects a separate, habituation-prone route that reduces saccade generation to irrelevant events. Functionally, this imbalance implies a recalibration within the saccade generator, preserving inhibitory capacity while constraining motor output. Our findings uncover a distinct form of oculomotor habituation and demonstrate how SI reveals dynamic decoupling of sensory input and motor output under repeated stimulation. Significance StatementThe ability to interrupt and resume eye movements in response to environmental changes is fundamental to visual exploration. We investigated how this process unfolds across repeated visual transients in naturalistic conditions. Our findings show that saccadic inhibition remains stable across time, whereas the subsequent rebound phase habituates. This dissociation suggests that distinct processes mediate reflexive interruption and motor recovery habituation. Our data indicate that dynamic modulation of motor gating circuits is a mechanism for optimizing oculomotor behavior. These results deepen our understanding of visual-motor coordination, provide insight about the constraints governing the underlying system circuitry, and may inform clinical tools for assessing sensorimotor adaptability in health and disease.

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bioRxiv2025

Visual performance fields during Saccadic Suppression of Image Displacement

Visual perception is not homogeneous throughout the visual field. Performance is generally better along the horizontal meridian compared to the vertical meridian, and in the lower compared to the upper visual field. These asymmetries in visual performance are reflected in structural asymmetries in early visual cortex. When exploring a visual scene, eye movements occur continuously, with visual perception resulting from a tight interplay between the visual as well as the oculomotor systems. Literature on visual performance across visual fields during saccades is limited, but existing studies show that perceptual performance during saccades is indistinguishable between the upper and the lower visual fields, or altogether better in the upper visual field compared to lower. In the current exploratory study, we asked participants to detect the direction of target displacement across visual fields, while performing a saccade as well as at fixation. During fixation and saccade viewing conditions, performance on the task was better along the horizontal compared to the vertical meridian. However, we did not observe a robust difference in performance between the lower and upper visual field, neither at fixation nor when participants were requested to perform saccades. We interpret our results based on known behavioural and neural anisotropies, as well as considering evolutionary approaches to the perception-action cycle.

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bioRxiv2025

The Influence of Spatial Frequencies, Orientation and Familiarity on Face Stimuli Integration

When we observe an object, our visual system identifies its shape and integrates it with specific details to form a coherent representation. This coarse-to-fine approach involves rapid processing of low spatial frequency (LSF) content to generate a basic template, which aids the integration of the more detailed high spatial frequency (HSF) information. Here we explore with two experiments how the contribution of LSF and HSF integration extends to face processing. To do so, we leveraged the face inversion effect, whereby inverted faces are more difficult to recognize than upright ones. In Experiment 1, ten participants matched two familiar faces displayed in rapid succession (template and probe face, respectively). The template and the probe shared either the same SF (congruent) or had complementary SF (incongruent). In congruent conditions, HSF templates yielded better matching accuracy than LSF templates. However, in incongruent conditions, mapping LSF probes onto HSF templates was more effective, but only for upright faces. We propose that, depending on the task, holistic processing may be facilitated by detailed information. In Experiment 2, twelve participants performed the same task with both familiar and unfamiliar faces. While for familiar faces the effects were the same as Experiment 1, for unfamiliar faces the overall accuracy was better for congruent than incongruent conditions, and, crucially, it was independent of the template SF. Our results challenge the view that LSF content provides a foundational template for integrating HSF information, and instead suggest a flexible encoding of SF information, that depends on image contingencies.

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bioRxiv2024

Contributions of temporal and spatial masking signals in perception of sequential visual events

Accurate perception of time and space is essential for moment-to-moment interactions with our surroundings. This process requires flexibility, as it integrates information from our actions and the external context. Probing the visual system during the updating process reveals spatiotemporal distortions, where sequential stimuli appear closer in time and space than they are. These effects occur perisaccadically or when a visual mask follows the stimuli. The study investigated whether non-overlapping visual masks could influence temporal inversion judgments (TOJs), suggesting that a temporal signal might act as an anchor during updating. In Experiment 1, participants judged the temporal order of two stimuli under three conditions: no mask, a full-field mask, or a partial mask avoiding stimulis locations. Compared to no mask, both masks triggered TOJs when presented within 30 milliseconds of the second stimulus. In a control experiment, delaying mask onset by 30 milliseconds eliminated the inversion effect. In Experiment 2, TOJs were observed for both ipsilateral and contralateral masks, suggesting that long range inhibitory signals might also contribute to the effect. Together, these findings indicate that temporal inversions can occur with non-overlapping stimuli masks configuration, pointing to a non-spatial signal related to mask timing as the underlying mechanism.

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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.

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bioRxiv2024

Proximity to Visual Stimuli Reduces Post-Saccadic Alpha Lateralisation

Posterior alpha lateralisation is a well-established marker of visual spatial attention, with growing evidence suggesting that it may also be linked to oculomotor planning and execution. However, saccades also result in a change in visual input to the fovea, which could be linked to lateralised posterior alpha. In this study, we investigate the interplay between saccade-induced foveal input changes and lateralised posterior alpha by analysing saccades from the cue period of a Posner task and the active feedback period of a neurofeedback task, where visual stimuli were present on screen. Specifically, we examine the impact of saccade landing proximity to visual stimuli and saccade amplitude on post-saccade alpha lateralisation. Consistent with previous research, we observe a general post-saccade alpha lateralisation across both tasks. Importantly, we find that alpha lateralisation is reduced in the neurofeedback task when saccades land close to visual stimuli compared to those landing further away, while saccade amplitude has no significant effect. This investigation highlights the importance of controlling for both eye movements and visual stimuli when investigating alpha lateralisation in fixational tasks. Moreover, it shows how both oculomotor and afferent processing mechanisms affect posterior alpha lateralisation.

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bioRxiv2024

Delineating In-Vivo T1-Weighted Intensity Profiles Within the Human Insula Cortex Using 7-Tesla MRI

The integral role of the insula cortex in sensory and cognitive function has been well documented in humans, and fine anatomical details characterising the insula have been extensively investigated ex-vivo in both human and non-human primates. However, in-vivo studies of insula anatomy in humans (in general), and within-insula parcellation (in particular) have been limited. The current study leverages 7 Tesla magnetic resonance imaging to delineate cortical depth intensity profiles within the human cortex. Our analysis revealed two separate clusters of relatively high and low signal intensity across the insula cortex located in three distinct compartments within the posterior, anterior-inferior, and middle insula. The posterior and anterior-inferior compartments are characterised by elevated T1-weighted signal intensities, contrasting with lower intensity observed in the middle insular compartment, compatible with ex-vivo studies. Importantly, the detection of the high T1-weighted anterior cluster is determined by the choice of brain atlas employed to define the insular ROI. We obtain reliable in-vivo within-insula parcellation at the individual and group levels, across two separate cohorts acquired in two separate sites (n1 = 21, Glasgow, UK; n2 = 101, Amsterdam, NL). Results are further confirmed by deriving cortical depth dependent profiles from T1Map and R1Map images. These results reflect new insights into the insula anatomical structure, in-vivo, while highlighting the use of 7 Tesla in neuroimaging with potential implications for individualised medicine approaches. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=125 SRC="FIGDIR/small/605123v3_ufig1.gif" ALT="Figure 1"> View larger version (51K): org.highwire.dtl.DTLVardef@1c27244org.highwire.dtl.DTLVardef@dbd256org.highwire.dtl.DTLVardef@1ce44f6org.highwire.dtl.DTLVardef@11183d0_HPS_FORMAT_FIGEXP M_FIG C_FIG

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bioRxiv2023

Contentopic mapping in ventral and dorsal association cortex: the topographical organization of manipulable object information

Understanding how object information is neurally organized is fundamental to unravel object recognition1-4. The best-known neural organizational principle of information is topographical mapping of specific dimensions. Such maps have been shown mainly for sensorimotor information within sensorimotor cortices (e.g., retinotopy)5-9. Thus, here we ask whether there are topographic maps - by analogy, contentopic maps - for mid-level object-related dimensions. We used functional magnetic resonance imaging and population receptive field analysis7 to measure tuning of neural populations to selected manipulable object-related dimensions. Here we show maps in dorsal and ventral occipital cortex that code for the score of each object on each target dimension in a linear progression following a particular direction along the cortical surface. Maps for each dimension are distinct, and consistent across individuals. Thus, object information is coded in multiple topographical maps - i.e., contentopic maps. These contentopic maps refer to intermediate level visual and visuomotor representations, and are potentially computed from the grouping of lower-level information through non-linear transformation following gestalt principles4,10. This shows that topography is a widespread and non-incidental strategy for the organization of information in the brain that leads to greatly reduced connectivity-related metabolic costs and fast and efficient readouts of information for stimuli discrimination11,12.

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bioRxiv2023

Data-driven estimates of the reproducibility of univariate BWAS are biased.

Recent studies have used big neuroimaging datasets to answer an important question: how many subjects are required for reproducible brain-wide association studies? These data-driven approaches could be considered a framework for testing the reproducibility of several neuroimaging models and measures. Here we test part of this framework, namely estimates of statistical errors of univariate brain-behaviour associations obtained from resampling large datasets with replacement. We demonstrate that reported estimates of statistical errors are largely a consequence of bias introduced by random effects when sampling with replacement close to the full sample size. We show that future meta-analyses can largely avoid these biases by only resampling up to 10% of the full sample size. We discuss implications that reproducing mass-univariate association studies requires tens-of-thousands of participants, urging researchers to adopt other methodological approaches.

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bioRxiv2023

The neural organization of visual information in the auditory cortex of the congenitally deaf

Neuroplasticity is the ability of the human brain to reorganize and modify its activity throughout life. In congenital deafness, sensory-deprived cortex can be recruited to represent sensory information belonging to other modalities, a process known as cross-modal plasticity. Previous studies have indicated that the auditory cortex of congenitally deaf, but not of hearing individuals, is recruited during visual tasks. However, it is not clear to what extent, and how, these cross-modal responses in the deprived auditory cortex represent low-level visual spatial information or map the visual field. Here, we addressed this question directly in an fMRI case-study, aiming to map retinotopic features in the auditory cortex. Two congenitally deaf and one hearing participant went through a conventional retinotopy fMRI experiment with visual stimuli designed to map the visual system. Using population receptive field (pRF) modelling, we revealed retinotopic-related responses in the auditory cortex of the deaf, but not in the hearing. These responses, that were mostly lateralized to the right hemisphere, represented the contralateral visual field, and were characterized by large receptive fields, centred to near foveal areas. Interestingly, we found that these responses to visual stimuli predominantly reflected negative BOLD signals in the auditory cortex of the deaf, suggesting that visual information might be represented through cross-modal deactivation signals.

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bioRxiv2023

Neural and behavioral signatures of the multidimensionality of manipulable object processing.

Understanding how we recognize everyday objects requires unravelling the variables that govern the way we think about objects and the way in which our representations are organized neurally. A major hypothesis is that the organization of object knowledge follows key object-related dimensions, analogously to how sensory information is organized in the brain. Here, we explored, behaviorally and neurally, the multidimensionality of object processing. We focused on within-domain object information as a proxy for the kinds of object decision tasks we typically engage in our daily lives - e.g., identifying a knife from other types of manipulable objects such as spoons, axes or screwdrivers. To do so, we extracted object-related dimensions from subjective human judgments on a set of objects from a particular object domain - i.e., manipulable objects. We demonstrated that the extracted dimensions are cognitively interpretable - i.e., participants are able to label them; are cognitively relevant for manipulable object processing - i.e., categorization decisions are guided by these dimensions; and are important for the neural organization of knowledge - i.e., they are good predictors of the neural signals elicited by manipulable objects. This shows that multidimensionality is a hallmark of the organization of object knowledge in the brain.

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bioRxiv2022

The 3D Structural Architecture of the Human Hand Area is Non-Topographic

The functional topography of the human primary somatosensory cortex (S1) hand area is a widely studied model system to understand sensory organization and plasticity. It is so far unclear whether or not the underlying 3D structural architecture also shows a topographic organization. We used 7T MRI data to quantify layer-specific myelin, iron and mineralization in relation to population receptive field maps of individual finger representations in Brodman area 3b (BA 3b) of human S1 in female and male younger adults. This 3D description allowed us to identify a characteristic profile of layer-specific myelin and iron deposition in the BA 3b hand area, but revealed an absence of structural differences, an absence of low-myelin borders, and high similarity of 3D microstructure profiles between individual fingers. However, structural differences and borders were detected between the hand and face areas. We conclude that the 3D structural architecture of the human hand area is non-topographic, unlike in some monkey species, which suggests a high degree of flexibility for functional finger organization and a new perspective on human topographic plasticity. Significance StatementUsing ultra-high field MRI, we provide the first comprehensive in vivo description of the 3D structural architecture of the human BA 3b hand area in relation to functional population receptive field (pRF) maps. High similarity of precise finger-specific 3D profiles, together with an absence of structural differences and an absence of low-myelin borders between individual fingers, reveal the 3D structural architecture of the human hand area to be non-topographic. This suggests reduced structural limitations to cortical plasticity and reorganization, and allows for shared representational features across fingers.

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bioRxiv2022

Peri-saccadic visual sensitivity is higher in the upper visual field

Visual neural processing is distributed among a multitude of sensory and sensory-motor brain areas exhibiting varying degrees of functional specializations and spatial representational anisotropies. Such diversity raises the question of how perceptual performance is determined, at any one moment in time, during natural active visual behavior. Here, exploiting a known dichotomy between the primary visual cortex and superior colliculus in representing either the upper or lower visual fields, we asked whether peri-saccadic orientation identification performance is dominated by one or the other spatial anisotropy. Humans (48 participants, 29 females) reported the orientation of peri-saccadic upper visual field stimuli significantly better than lower visual field stimuli, unlike their performance during steady-state gaze fixation, and contrary to expected perceptual superiority in the lower visual field in the absence of saccades. Consistent with this, peri-saccadic superior colliculus visual neural responses in two male rhesus macaque monkeys were also significantly stronger in the upper visual field than in the lower visual field. Thus, peri-saccadic orientation identification performance is more in line with oculomotor, rather than visual, map spatial anisotropies. Significance statementDifferent brain areas respond to visual stimulation, but they differ in the degrees of functional specializations and spatial anisotropies that they exhibit. For example, the superior colliculus both responds to visual stimulation, like the primary visual cortex, and controls oculomotor behavior. Compared to the primary visual cortex, the superior colliculus exhibits an opposite pattern of upper/lower visual field anisotropy, being more sensitive to the upper visual field. Here, we show that human peri-saccadic orientation identification performance is better in the upper compared to the lower visual field. Consistent with this, monkey superior colliculus visual neural responses to peri-saccadic stimuli follow a similar pattern. Our results indicate that peri-saccadic perceptual performance reflects oculomotor, rather than visual, map spatial anisotropies.

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bioRxiv2021

Encoding of motion by spatial and temporal frequency in the human middle temporal cortex measured by 7T fMRI

Perception of dynamic scenes in our environment results from the evaluation of visual features such as the fundamental spatial and temporal frequency components of a moving object. The ratio between these two components represents the objects speed of motion. The human middle temporal cortex hMT+ has a crucial biological role in the direct encoding of object speed. However, the link between hMT+ speed encoding and the spatiotemporal frequency components of a moving object is still under explored. Here, we recorded high resolution 7T blood oxygen level-dependent BOLD responses to different visual motion stimuli as a function of their fundamental spatial and temporal frequency components. We fitted each hMT+ BOLD response with a 2D Gaussian model allowing for two different speed encoding mechanisms: 1) distinct and independent selectivity for the spatial and temporal frequencies of the visual motion stimuli 2) pure tuning for the speed of motion. We show that both mechanisms occur but in different neuronal groups within hMT+, with the largest subregion of the complex showing separable tuning for the spatial and temporal frequency of the visual stimuli. Both mechanisms were highly reproducible within participants, reconciling single cell recordings from MT in animals that have showed both encoding mechanisms. Our findings confirm that a more complex process is involved in the perception of speed than initially thought and suggest that hMT+ plays a primary role in the evaluation of the spatial features of the moving visual input.

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bioRxiv2019

Triple visual hemifield maps in optic chiasm hypoplasia

In humans, each hemisphere comprises an overlay of two visuotopic maps of the contralateral visual field, one from each eye. Is the capacity of the visual cortex limited to these two maps or are plastic mechanisms available to host more maps? Using an integrative approach of submillimeter fMRI, diffusion-weighted imaging and population receptive field mapping, we found three hemiretinal inputs to converge onto the left hemisphere in a rare individual with chiasma hypoplasia. This generates extremely atypical responses in striate and extrastriate cortices, specifically an overlay of three hemifield representations. Unexpectedly, the effects of this large abnormality on visual function in daily life are not easily detected. We conclude that developmental plasticity including the re-wiring of local intra- and cortico-cortical connections is pivotal to support the coexistence and functioning of three hemifield maps within one hemisphere.

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