Biology subjects

van Bree, S.

Publications and source records attributed to van Bree, S..

7 recordsLinked to original sources

bioRxiv2026

Shared and Distinct Object Spaces in Human and Macaque Inferotemporal Cortex

Human and macaque studies of inferotemporal cortex (IT) have shaped our understanding of object vision, yet the extent of their representational alignment and the precise nature of this correspondence have remained unclear. To address these questions, we applied multivariate cross-species alignment to large-scale macaque multi-unit recordings and human fMRI responses to the same 8,640 naturalistic object images. The resulting shared space revealed a surprisingly rich, high-dimensional geometry that extended well beyond coarse correspondences such as animacy and shape and included a wide range of interpretable visual and conceptual dimensions, as well as specific conjunctions of the two. Unexpectedly, the space also uncovered a shared neural signature for orthography-related content, consistent with precursor mechanisms in macaques. Contrasting the within-species spaces revealed systematic differences in the expression of living and artificial categories, conspecific content, and visual versus conceptual structure. Together, these findings uncover a high-dimensional shared object space along with species-specific divergences, clarifying the scope and limits of cross-species comparability.

neuroscience↗

bioRxiv2024

No evidence that visual impulses enhance the readout of retrieved long-term memory contents from EEG activity

The application of multivariate pattern analysis (MVPA) to electroencephalography (EEG) data allows neuroscientists to track neural representations at temporally fine-grained scales. This approach has been leveraged to study the locus and evolution of long-term memory contents in the brain, but a limiting factor is that decoding performance remains low. A key reason for this is that processes like encoding and retrieval are intrinsically dynamic across trials and participants, and this runs in tension with MVPA and other techniques that rely on consistently unfolding neural codes to generate predictions about memory contents. The presentation of visually perturbing stimuli may experimentally regularize brain dynamics, making neural codes more stable across measurements to enhance representational readouts. Such enhancements, which have repeatedly been demonstrated in working memory contexts, remain to our knowledge unexplored in long-term memory tasks. In this study, we evaluated whether visual perturbations--or pings--improve our ability to predict the category of retrieved images from EEG activity during cued recall. Overall, our findings suggest that while pings evoked a prominent neural response, they did not reliably produce improvements in MVPA-based classification across several analyses. We discuss possibilities that could explain these results, including the role of experimental and analysis parameter choices and mechanistic differences between working and long-term memory.

neuroscience↗

bioRxiv2022

Phase separation of competing memories along the human hippocampal theta rhythm.

Competition between overlapping memories is considered one of the major causes of forgetting and it is still unknown how the human brain resolves such mnemonic conflict. In the present MEG study, we empirically tested a computational model that leverages an oscillating inhibition algorithm to minimise overlap between memories. We used a proactive interference task, where a reminder word could be associated with either a single image (non-competitive condition) or two competing images, and participants were asked to always recall the most recently learned word-image association. Time-resolved pattern classifiers were trained to detect the reactivated content of target and competitor memories from MEG sensor patterns, and the timing of these neural reactivations was analysed relative to the phase of the dominant hippocampal 3Hz theta oscillation. In line with our preregistered hypotheses, target and competitor reactivations locked to different phases of the hippocampal theta rhythm after several repeated recalls. Participants who behaviourally experienced lower levels of interference also showed larger phase separation between the two overlapping memories. The findings provide evidence that the temporal segregation of memories, orchestrated by slow oscillations, plays a functional role in resolving mnemonic competition by separating and prioritising relevant memories under conditions of high interference.

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bioRxiv2021

The spotlight of attention turns from rhythmic exploration-exploitation to a stable exploitation state

While traditional studies claim that visuospatial attention stays fixed at one location at a time, recent research has rather shown that attention rhythmically fluctuates between different locations at rates of prominent brain rhythms. However, little is known about the temporal dynamics of this fluctuation and, particularly, whether it changes over time. Thus, we addressed this question by investigating how visuospatial attention behaves over space and time. We recorded electroencephalographic activity of twenty-seven human participants while they performed a visuospatial cueing task, where attention was covertly oriented to the left or right visual field. In order to decode the spatial locus of attention from neural activity, we trained and tested a classifier on every timepoint of the orienting period, from the attentional cue to stimulus onset. This resulted in one temporal generalization matrix per participant, which was time-frequency decomposed to identify the sampling rhythm. Finally, a searchlight analysis was conducted to reveal the brain regions responsible for attention allocation. Our results show a dynamic evolution of the attentional spotlight, distinguishing between two states. In an early time window, attention explored both cued and uncued hemifield rhythmically at ~10 Hz. In a later time window attention focused on the cued hemifield. Classification was driven by occipital sources, while frontal regions exclusively became involved just before the spotlight settled onto the cued location. Together, our results define attentional sampling as a quasi-rhythmic dynamic process characterized by an initial rhythmic exploration-exploitation state, which is followed by a stable exploitation state.

neuroscience↗

bioRxiv2021

Clock time: a foreign measure to brain dynamics

Human thought is highly flexible, achieved by evolving patterns of brain activity across groups of cells. Neuroscience aims to understand cognition in the brain by analysing these intricate patterns. We argue this goal is impeded by the time format of our data - clock time. The brain is a system with its own dynamics and regime of time, with no intrinsic concern for the human-invented second. Here, we present the Brain Time Toolbox, a software library that retunes electrophysiology data in line with oscillations that orchestrate neural patterns of cognition. These oscillations continually slow down, speed up, and undergo abrupt changes, introducing a disharmony between the brains internal regime and clock time. The toolbox overcomes this disharmony by warping the data to the dynamics of coordinating oscillations, setting oscillatory cycles as the datas new time axis. This enables the study of neural patterns as they unfold in the brain, aiding neuroscientific inquiry into dynamic cognition. In support of this, we demonstrate that the toolbox can reveal results that are absent in a default clock time format.

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bioRxiv2020

Sustained neural rhythms reveal endogenous oscillations supporting speech perception

Rhythmic sensory or electrical stimulation will produce rhythmic brain responses. These rhythmic responses are often interpreted as endogenous neural oscillations aligned (or "entrained") to the stimulus rhythm. However, stimulus-aligned brain responses can also be explained as a sequence of evoked responses, which only appear regular due to the rhythmicity of the stimulus, without necessarily involving underlying neural oscillations. To distinguish evoked responses from true oscillatory activity, we tested whether rhythmic stimulation produces oscillatory responses which continue after the end of the stimulus. Such sustained effects provide evidence for true involvement of neural oscillations. In Experiment 1, we found that rhythmic intelligible, but not unintelligible speech produces oscillatory responses in magnetoencephalography (MEG) which outlast the stimulus at parietal sensors. In Experiment 2, we found that transcranial alternating current stimulation (tACS) leads to rhythmic fluctuations in speech perception outcomes after the end of electrical stimulation. We further report that the phase relation between electroencephalography (EEG) responses and rhythmic intelligible speech can predict the tACS phase that leads to most accurate speech perception. Together, we provide fundamental results for several lines of research - including neural entrainment and tACS - and reveal endogenous neural oscillations as a key underlying principle for speech perception.

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bioRxiv2019

Does alpha phase modulate visual target detection? Three experiments with tACS phase-based stimulus presentation.

In recent years the influence of alpha (7-13 Hz) phase on visual processing has received a lot of attention. Magneto-/encephalography (M/EEG) studies showed that alpha phase indexes visual excitability and task performance. If occipital alpha phase is functionally relevant, the phase of occipital alpha-frequency transcranial alternating current stimulation (tACS) could modulate visual processing. Visual stimuli presented at different pre-determined, experimentally controlled, phases of the entraining tACS signal should then result in an oscillatory pattern of visual performance. We studied this in a series of experiments. In experiment one, we applied 10 Hz tACS to right occipital cortex (O2) and used independent psychophysical staircases to obtain contrast thresholds for detection of visual gratings in left or right hemifield, in six equidistant tACS phase conditions. In experiments two and three, tACS was at EEG-based individual peak alpha frequency. In experiment two, we measured detection rates for gratings with (pseudo-)fixed contrast levels. In experiment three, participants detected brief luminance changes in a custom-built LED device, at eight equidistant alpha phases. In none of the experiments did the primary outcome measure over phase conditions consistently reflect a one-cycle sinusoid as predicted. However, post-hoc analyses of reaction times (RT) suggested that tACS alpha phase did modulate RT in both experiments 1 and 2 (not measured in experiment 3). This observation is in line with the idea that alpha phase causally gates visual inputs through cortical excitability modulation.

neuroscience↗