Biology subjects

Roberts, M. J.

Publications and source records attributed to Roberts, M. J..

10 recordsLinked to original sources

bioRxiv2026

Item-specific clustering of high gamma-band activity on theta phase during speech categorization

Theta-gamma phase-amplitude coupling (PAC) has been proposed as a mechanism for separating neural representations in time. Although item-specific PAC has been reported, its role in perception remains unclear. Notably, previous work has shown that theta phase can bias perception, raising the question whether such biases are linked to phase-specific gamma activity. Here, we investigated whether phase-dependent perceptual biases are accompanied by item-specific theta-gamma PAC. We presented ambiguous speech sounds that could be interpreted as either /da/ or /ga/ in patients with epilepsy implanted with intracranial electrocorticography. We found that pre-stimulus theta phase predicted both the neural and perceptual response, with /da/ and /ga/ tuned channels exhibiting gamma activity clustering at distinct theta phases. These findings suggest that neural and perceptual biases stem from phase-specific pre-activation of item-specific neural representations. They demonstrate the generalizability of the theta-gamma code, shaping behavior and enhancing representational capacity.

neuroscience↗

bioRxiv2026

Stimulus dependent modulation of perceptual filling-in is predicted by the properties of early visual cortex

Filling-in occurs during the perceptual disappearance of a blank figure presented on a textured background. Current models of perceptual filling-in are based on a two-stage model where the figure boundary weakens after a period of adaptation, followed by the spreading of the background representation into the region representing the figure. This suggests a competition between figure boundary and background representations whereby filling-in is facilitated by a weaker boundary representation and a stronger background representation. Here, we test this interpretation, by using the oblique effect and surround-modulation suppression, which are functional properties of early visual cortex that modulate the expected strengths of the responses to the background texture and to the figure boundary. In a sample of N=58 participants, we found more filling-in with background textures of cardinal compared to oblique orientations (earlier onset time, with more and longer episodes of filling-in per trial), in line with a known, stronger neuronal response for cardinal than for oblique orientation in early visual cortex. We found more filling-in when the main axis of the rectangular figure was iso-oriented rather than cross-oriented with the background texture (more and longer episodes of filling-in per trial, but no change in onset time), in line with a lower response to oriented stimuli when surrounded by iso-oriented flankers compared to cross-oriented flankers. Overall, our results support the two-stage model and suggest the involvement of early visual cortical areas characterized by the oblique effect and orientation-tuned surround-suppression.

neuroscience↗

bioRxiv2026

Feedback to deep layers in human V1 during perceptual filling-in

Visual surface perception is a fundamental aspect of vision, yet its neural implementation remains poorly understood. Troxlers perceptual filling-in paradigm provides a tractable illusion for studying surface perception, in which a peripheral figure becomes perceptually assimilated into the surrounding background after a period of sustained fixation. Although neural correlates of this phenomenon have been reported in early visual cortex, the underlying mechanisms, particularly the contribution of feedback signaling, remain unresolved. Here we use ultra-high-field (7T) layer-fMRI to investigate perceptual filling-in in the human visual cortex. While experimentally controlling perceptual filling-in, we measured GE-BOLD responses in ten participants. Analyses across cortical depth in the independently localized figure representation in primary visual cortex (V1) revealed neural correlates of filling-in in deep cortical layers, which are associated with feedback input. These findings provide evidence that perceptual filling-in and visual surface perception in general are supported by feedback signals to early visual cortex.

neuroscience↗

bioRxiv2025

Context-dependent benefits of training and reminders in visual skill learning

Previous studies using a visual texture discrimination task (TDT) have demonstrated that performance enhancements resulting from extensive daily training (full training condition) remained intact after replacing all training, except for the first and last session, with a few daily reminder trials (reminder condition). Omitting reminders (control condition) yielded only limited learning, supporting their crucial contribution. We first confirmed these findings and excluded gaze position differences among conditions as a contributing factor. Next, we tested whether the reminders effectiveness is specific to a context of limited attention to the peripheral target caused by simultaneously performing a demanding fixation task. Removing the fixation task yielded performance levels in the first session matching those normally reached after lengthy daily training, suggesting that learning in the standard TDT involves the redeployment of attention. After changing texture parameters to increase the difficulty of the task, performing the TDT without a fixation task yielded learning in all three conditions. This indicates that in a dual-task, reminders can produce learning outcomes comparable to full training. In contrast, when the TDT is performed with full attention to the target, consolidation of the initial session alone can yield improvements equivalent to those observed in reminder and full training conditions.

neuroscience↗

bioRxiv2025

Unveiling early visual cortical mechanisms in perceptual filling-in: a parametric study of eccentricity and movement dependence

Surface perception relies on interactions between boundary encoding and surface filling-in. In a perceptual filling-in paradigm, a blank figure becomes perceptually replaced by a textured background after prolonged fixation of a point away from the figure. Filling-in begins when neurons representing the figures boundary adapt, allowing background-related activity to spread into the figures retinotopic representation. Adaptation proceeds faster the better the boundary is stabilized in a neurons receptive field (RF). We hypothesized that moving the figure boundary beyond a neurons RF would reduce adaptation and hinder filling-in, with larger movements permitting progressively less filling-in. As RF size increases with eccentricity, we further hypothesized that greater eccentricities would require larger movements to interfere with filling-in. Our results confirmed both predictions. The reduction in filling-in duration with increasing motion range permitted estimating RF size at each eccentricity. The slope of a linear function relating RF size to eccentricity matched values reported in human fMRI studies of V1/V2, suggesting that boundary adaptation involves early visual areas. We also explored whether microsaccade amplitude affects filling-in, but found no supporting evidence. Thus, external figure motion and microsaccades may disrupt adaptation through different mechanisms. These findings provide new insights into neural adaptation processes preceding perceptual filling-in.

neuroscience↗

bioRxiv2025

Conserved Aberrant Developmental Trajectories of Human and Mouse SBMA Motor Neurons

Spinal bulbar muscular atrophy (SBMA) is a neuromuscular disease caused by a polyglutamine repeat expansion in the androgen receptor gene (AR). Lower motor neuron loss is a key feature of the disease, yet it remains poorly understood why these cells are affected. The transcriptional mechanisms underlying SBMA pathogenesis and how these evolve across developmental and disease stages remains incompletely defined. To elucidate the molecular mechanisms underlying motor neuron loss in SBMA, we first performed transcriptomic profiling of both induced pluripotent stem cell derived motor neurons (iPSC-MNs) generated from SBMA patients and laser-captured micro dissected motor neurons (LCM-MNs) from symptomatic AR100 SBMA mice. We compared differential gene expression between the two models to identify shared transcriptional programs. To address the temporal progression of molecular changes we conducted profiling at key stages of motor neurogenesis in the developing iPSC-MNs and at pre-symptomatic and end-stage disease in AR100 SBMA mice to elucidate the emergence of the transcriptional phenotype and the trajectory of the gene expression changes. We found significant transcriptional convergence between these two species. Notably, shared dysregulation was observed in pathways related to the spliceosome, the cell cycle and mitochondrial function. These transcriptional alterations emerged early in motor neurogenesis suggesting a developmental component to SBMA. Further in AR100 LCM-MNs we also observed disruption of mitochondrial and DNA damage repair pathways from pre-symptomatic to end stage disease. This study identifies conserved pathogenic mechanisms across two SBMA model systems and provides crucial insights into the molecular basis and temporal dynamics of SBMA progression which may help identify potential therapeutic targets for SBMA. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/674754v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@1577034org.highwire.dtl.DTLVardef@187824eorg.highwire.dtl.DTLVardef@17bf6a5org.highwire.dtl.DTLVardef@17e09f9_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

Revisiting alpha-theta cross-frequency dynamics during working memory

Prior Electroencephalography (EEG) research has shown that during working memory delay, alpha (8-14 Hz) and theta (4-8 Hz) oscillations tend to form a 2:1 frequency ratio. According to the Binary Hierarchy Brain Body Oscillation Theory (BHBBOT), a recent model grounded in mathematical analysis, such harmonic (2:1) alpha:theta frequency configurations reflect enhanced connectivity between brain regions generating these rhythms. However, this prediction has not yet been empirically tested. In this study, we leveraged Information Theory and the Theory of Weakly Coupled Oscillators (TWCO) to examine whether the previously observed frequency modulations in alpha and theta rhythms during working memory are accompanied by changes in inter-areal connectivity. Contrary to the BHBBOT predictions, both Information Theory metrics and TWCO parameters showed that connectivity between frontal theta and parietal alpha rhythms was significantly reduced during the working-memory delay period (while the proportion of 2:1 ratios increased). In addition, phase locking value, a standard measure of synchrony, was also significantly reduced during working memory delay and was negatively associated with behavioural performance. In conclusion, our results show that the increased occurrence of 2:1 alpha:theta cross-frequency ratios during working memory reflects functional segregation (rather than integration) between frontal and parietal regions.

neuroscience↗

bioRxiv2024

Gamma Synchrony Mediates Figure-Ground Perception

Gamma synchrony is ubiquitous in visual cortex, but whether it contributes to perceptual grouping remains contentious based on observations that gamma frequency is not consistent across stimulus features and that gamma synchrony depends on distances between image elements. These stimulus dependencies have been argued to challenge the idea that the visual system groups image elements by synchronizing the neural assemblies that encode them. Here we argue instead that these dependencies may shape synchrony in perceptually meaningful ways. Indeed, according to the theory of weakly coupled oscillators (TWCO), synchrony-based grouping mechanisms require stimulus dependence. Synchronization among coupled oscillators depends on frequency dissimilarity and coupling strength, which in early visual cortex relate to local feature dissimilarity and physical distance, respectively. We manipulated these factors in a texture segregation experiment wherein human observers identified the orientation of a figure defined by reduced contrast heterogeneity compared to the background. Human performance followed TWCO predictions both qualitatively and quantitatively, as formalized in a computational model. Moreover, we found that when enriched with a Hebbian learning rule, our model also predicted human learning effects: Increases in model gamma synchrony due to perceptual learning predicted improvements in texture segregation across sessions. Taken together, our data suggest that the stimulus-dependence of gamma synchrony captures local image statistics and is linked to the stimulus-dependence of texture segregation, and that the effect of visual experience on gamma synchrony provides a viable perceptual learning mechanism for training-induced improvements in texture segregation. Our results suggest that gamma synchrony with its inherent stimulus dependencies can provide a plausible mechanistic basis for perceptual grouping and visual scene segmentation.

neuroscience↗

bioRxiv2022

Spatiotemporal patterns of sleep spindle activity in human anterior thalamus and cortex

Sleep spindles (8 - 16 Hz) are transient electrophysiological events during non-rapid eye movement sleep. While sleep spindles are routinely observed in the cortex using scalp electroencephalography (EEG), recordings of their thalamic counterparts have not been widely studied in humans. Based on a few existing studies, it has been hypothesized that spindles occur as largely local phenomena. We investigated intra-thalamic and thalamocortical spindle co-occurrence, which may underlie thalamocortical communication. We obtained scalp EEG and thalamic recordings from 7 patients that received bilateral deep brain stimulation (DBS) electrodes to the anterior thalamus for the treatment of drug resistant focal epilepsy. Spindles were categorized into subtypes based on their main frequency (i.e., slow (10{+/-}2 Hz) or fast (14{+/-}2 Hz)) and their level of thalamic involvement (spanning one channel, or spreading uni- or bilaterally within the thalamus). For the first time, we contrasted observed spindle patterns with permuted data to estimate random spindle co-occurrence. We found that multichannel spindle patterns were systematically coordinated at the thalamic and thalamocortical level. Importantly, distinct topographical patterns of thalamocortical spindle overlap were associated with slow and fast subtypes of spindles. These observations provide further evidence for coordinated spindle activity in thalamocortical networks. HighlightsO_LISleep spindles were measured in human anterior thalamus and on the scalp C_LIO_LIBoth fast and slow spindles occurred in the anterior thalamus C_LIO_LI> 25% of spindles spanned multiple channels in thalamus and cortex C_LIO_LIA novel statistical approach confirmed that spindle co-occurrences were not random C_LIO_LICortical spindle patterns depended on thalamic involvement and spindle frequency C_LI

neuroscience↗

bioRxiv2019

A novel approach for combining task-dependent gamma with alpha and beta power modulation for enhanced identification of eloquent cortical areas using ECoG in patients with medical-refractory epilepsy

Electrical stimulation mapping (ESM) is the gold standard for identification of \"eloquent\" areas prior to resection of epileptogenic tissue, however, it is time consuming and may cause side effects, especially stimulation-induced seizures and after-discharges. Broadband gamma activity (55 - 200 Hz) recorded with subdural electrocorticography (ECoG) during cognitive tasks has been proposed as an attractive tool for mapping cortical areas with specific function but until now has not proven definitive clinical value. Fewer studies have addressed whether the alpha (8 - 12 Hz) and beta (15 - 25 Hz) band activity could also be used to improve eloquent cortex identification. We compared alpha, beta and broadband gamma activity, and their combination for the identification of eloquent cortical areas defined by ESM. Ten patients participated in a delayed-match-to-sample task, where syllable sounds were matched to visually presented letters and responses given by keyboard. We used a generalized linear model (GLM) approach to find the optimal weighting of low frequency bands and broadband gamma power to predict the ESM categories. Broadband gamma activity increased more in eloquent areas than in non-eloquent areas and this difference had a diagnostic ability (area under (AU) the receiving operating characteristic curve - AUROC) of [~]70%. Both alpha and beta power decreased more in eloquent areas. Alpha power had lower AUROC than broadband gamma while beta had similar AUROC. AUROC was enhanced by the combination of alpha and broadband gamma (3% improvement) and by the combination of beta and broadband gamma (7% improvement) over the use of broadband gamma alone. Further analysis showed that the relative performance of broadband gamma and low frequency bands depended on multiple factors including the time period of the cognitive task, the location of the electrodes and the patients attention to the stimulus. However, the combination of beta band and broadband gamma always gave the best performance. We show how ECoG power modulation from cognitive testing periods can be used to map the probability of eloquence by ESM and how this probability can be used as an aid for optimal ESM planning. We conclude that low frequency power during cognitive testing can contribute to the identification of eloquent areas in patients with focal refractory epilepsy improving its precision but does not replace the need of ESM.\n\nHighlightsO_LIGamma, alpha and beta band activity has significant diagnostic ability to identify ESM defined eloquent cortical areas.\nC_LIO_LIWe present a novel method to combine gamma and low frequency activity for enhanced identification.\nC_LIO_LIWe quantify how identification is dependent on analysis time window, cortical function, and patients attentional engagement.\nC_LIO_LIWith further development, this approach may offer an alternative to ESM mapping with reduced burden for patients.\nC_LI

neuroscience↗