Biology subjects

Bowman, H.

Publications and source records attributed to Bowman, H..

At least 19 recordsLinked to original sources

bioRxiv2026

Beyond Rate: Hippocampal Phase Codes for Space and Memory

Place cells and concept neurons are defined by a rise in firing rate at a particular location or for a particular person or object. Neurons without such a rise remain unlabeled, although they keep firing during the task. Such neurons could still carry information in the timing of their spikes. Hippocampal theta provides a reference for this timing. We therefore asked whether the theta phase of a neuron's spikes depends on location or on the viewed image, even when its firing rate does not. We analysed hippocampal neurons in humans navigating a virtual city, rats running on a linear track, and humans viewing images of anima ls, faces, and places. In both navigation datasets, more neurons than expected by chance fired at a consistent theta phase at particular locations. This phase tuning remained after we excluded neurons whose firing rate depended on location. In human navigation, the spike phases of these remaining neurons improved location decoding beyond the firing rates of all neurons. More phase-tuned neurons than expected by chance also fired at progressively earlier theta phases as participants passed each neuron's preferred location. This pattern resembles phase precession, which classically occurs as an animal crosses the firing-rate field of a place cell. The neurons that showed it had no firing-rate field, so their phase shift was anchored to the location defined by phase tuning alone. During image viewing, more neurons than expected by chance changed the theta phase of their spikes after a particular image appeared. This effect remained after we removed, for each neuron, the images that changed its firing rate. Spike phases alone also predicted the image category above chance. Theta-relative spike timing therefore carries in formation about location and images that firing rate alone misses. We propose that weak input changes when a neuron fires with in the theta cycle, whereas strong input also raises its firing rate.

neuroscience↗

bioRxiv2026

The 2-feature Simultaneous Type/ Serial Token Model of temporal feature conjunctions: Successes are merely fortunate conjunctions.

Resolving the binding problem, i.e., how we integrate perceptual features in space and time to perceive objects, people and events as coherent wholes instead of masses of free-floating features, has been a central goal of cognitive scientists for decades. Conjunction errors occur whenever features are mis-bound leading to illusory percepts that were not actually presented. A specific kind of Rapid Serial Visual Presentation experiment induces temporal illusory conjunctions, called distractor intrusion errors. Despite these errors being well-established, current theories and models provide limited explanations. We present the 2-feature Simultaneous Type/Serial Token (2f-ST2) Model, the latest addition to the family of ST2-models, which simulates the most important behavioural and electrophysiological distractor intrusion findings. These include response distributions, reaction time patterns, and evoked electrophysiology responses. Importantly, we simulate these results across diverse empirical paradigms, implementing a range of stimulus sets, temporal dynamics, and involving multiple responses after each trial, without needing to modify our model's architecture or core parameters. Our findings are discussed in relation to theories of selective attention and working-memory binding. We argue that the 2f-ST2 model is more parsimonious than the leading theory of distractor-intrusions (the focussed-attention/sophisticated-guessing model), since it uses only a single binding mechanism, implying that correct bindings are simply fortunate conjunctions. The 2f-ST2 model further makes predictions for stimulus-competition, subjective-visibility and human electrophysiology. In summary, the ST2-model is a general framework for understanding how perception, temporal attention and working-memory interact, and the 2f-ST2 model extends the framework to distractor intrusions, thus explaining temporal feature binding.

neuroscience↗

bioRxiv2025

The Missing Memory Imprint

We provide evidence that the brain searches for salient stimuli below the level of conscious awareness. We show that, while targets are found very efficiently in Rapid Serial Visual Presentation (RSVP), distractors do not leave a strong memory trace, especially if the memory probe is unexpected. This fits with traditional theories of late attentional selection, whereby "correct rejections" of non-targets are performed with very little processing cost. Our findings are also consistent with the tokenized percept theory of conscious perception, one element of which is that conscious awareness is required to provide sustained representations.

animal behavior and cognition↗

bioRxiv2025

Breakthrough Percepts of Familiar Faces

In Rapid Serial Visual Presentation (RSVP), the vast majority of stimuli are not consciously perceived, but the salient ones breakthrough into awareness and can be reported. In addition, these breakthrough events are observable with EEG, since they generate a P3 or other distinguishing components. The Fringe-P3 method is based upon these characteristics. Concealed knowledge studies have successfully employed this Fringe-P3 method using own-name and own email-address, with the method being shown to be less vulnerable to counter-measures than other approaches. It has also been shown that famous faces presented in RSVP differentially break into awareness and generate a distinct evoked response component. In this paper, we further enhance the applicability of the Fringe-P3 concealed knowledge test by demonstrating the effectiveness of the method on personally-familiar faces. While salient, such stimuli do not have the exquisite salience of famous faces, being a better match to the level of salience that might be found in forensic applications. Our findings suggest that the Fringe-P3 method could be used to detect intrinsic salience of familiar faces, even when there was no task associated with these faces. We investigated the sensitivity of the ERP-based RSVP paradigm to infer recognition of familiar faces, and performed statistical inference in the Time and Frequency domains, to differentiate between known and unknown faces, at group and participant levels.

neuroscience↗

bioRxiv2024

Beyond EEG Onset Transients: Sensitisation and Habituation of Hyper-excitation to Constant Presentation and Offset ofPattern-Glare Stimuli

Pattern-glare, characterised by visual distortions, discomfort, and stress when viewing striped patterns, has been associated with cortical hyperexcitability, particularly in individuals with visually induced epilepsy, migraines, and visual stress. While previous studies have explored the onset transients of such stimuli, this research investigates the sensitisation and habituation effect to the constant presentation and offset of pattern-glare stimuli. We analysed the temporal characteristics of the Event Related Potentials (ERPs) in healthy participants to find correlates of cortical hyperexcitability over two time granularities: a fine granularity (over seconds) and a coarser granularity (across the time-course of the entire experiment). We looked for habituation and sensitization effects across these time periods. Our results suggest that brain responses to pattern-glare stimuli are correlated to participants sensitivity to visual discomfort with statistically significant effects observed for this factor and for its interaction with changes over time. This study improves our understanding of how the brain adapts to persistent visual stimuli and provides insights that may inform treatments for conditions like migraine and epilepsy.

neuroscience↗

bioRxiv2024

Headache-specific Hyperexcitation Sensitises and Habituates on different Time Scales: An Event Related Potential study of Pattern-Glare

Cortical hyperexcitability is a key pathophysiological feature in several neurological disorders, including migraine, epilepsy, tinnitus, and Alzheimers disease. We examined the temporal characteristics of Evoked Related Potentials (ERPs) in a healthy population using the Pattern Glare Test, a diagnostic tool used to assess patients with sensitivity to cortical hyperexcitability. During the experiment, participants recorded state measures with this study focussing on susceptibility to migraine. We investigated two timeframes: habituation over the course of the experiment and sensitization over the course of stimulus presentation. We found evidence of hyperexcitability in the visual cortex, for the clinically aggravating stimuli (medium). Participants who reported a higher state measure exhibited a higher degree of habituation and sensitization, which was dependent on susceptibility to migraine. These findings suggest that the same experimental paradigm and analysis should be performed on a clinically diagnosed population.

neuroscience↗

bioRxiv2021

Hippocampal neurons code individual memory episodes in humans

The hippocampus is an essential hub for episodic memory processing. However, how human hippocampal single neurons code multi-element associations remains unknown. Some argue that each hippocampal neuron codes for an invariant element within an episode. Instead, others have proposed that hippocampal neurons bind together all elements present in a discrete episodic memory. Here, we provide evidence for the latter. We show that individual neurons, which we term Episode Specific Neurons (ESNs), code discrete episodic memories using either a rate code or a temporal firing code. We find evidence for these neurons exclusively in the hippocampus. Importantly, these ESNs do not reflect the coding of a particular element in the episode (i.e., concept or time). Instead, they code for the conjunction of the different elements that make up the episode. One-Sentence SummaryIndividual neurons in the hippocampus code for discrete episodic memories.

neuroscience↗

bioRxiv2021

Concealed identity information detection with pupillometry in rapid serial visual presentation

The concealed information test (CIT) relies on bodily reactions to stimuli that are hidden in mind. However, people can use countermeasures, such as purposely focusing on irrelevant things, to confound the CIT. A new method designed to prevent countermeasures uses rapid serial visual presentation (RSVP) to present stimuli on the fringe of awareness. Previous studies that used RSVP in combination with electroencephalography (EEG) showed that participants exhibit a clear reaction to their real first name, even when they try to prevent such a reaction (i.e., when their name is concealed information). Since EEG is not easily applicable outside the laboratory, we investigated here whether pupil size, which is easier to measure, can also be used to detect concealed identity information. In our first study, participants adopted a fake name, and searched for this name in an RSVP task, while their pupil sizes were recorded. Apart from this fake name, their real name and a control name also appeared in the task. We found pupil dilation in response to the task-irrelevant real name, as compared to control names. However, while most participants showed this effect qualitatively, it was not statistically significant for most participants individually. In a second study, we preregistered the proof-of-concept methodology and replicated the original findings. Taken together, our results show that the current RSVP task with pupillometry can detect concealed identity information at a group level. Further development of the method is needed to create a valid and reliable concealed identity information detector at the individual level.

physiology↗

bioRxiv2020

How hot is the hot zone? Computational modelling clarifies the role of parietal and frontoparietal connectivity during anaesthetic-induced loss of consciousness

In recent years, specific cortical networks have been proposed to be crucial for sustaining consciousness, including the posterior hot zone and frontoparietal resting state networks (RSN). Here, we computationally evaluate the relative contributions of three RSNs - the default mode network (DMN), the salience network (SAL), and the central executive network (CEN) - to consciousness and its loss during propofol anaesthesia. Specifically, we use dynamic causal modelling (DCM) of 10 minutes of high-density EEG recordings (N = 10, 4 males) obtained during behavioural responsiveness, unconsciousness and post-anaesthetic recovery to characterise differences in effective connectivity within frontal areas, the posterior "hot zone", frontoparietal connections, and between-RSN connections. We estimate - for the first time - a large DCM model (LAR) of resting EEG, combining the three RSNs into a rich club of interconnectivity. Consistent with the hot zone theory, our findings demonstrate reductions in inter-RSN connectivity in the parietal cortex. Within the DMN itself, the strongest reductions are in feed-forward frontoparietal and parietal connections at the precuneus node. Within the SAL and CEN, loss of consciousness generates small increases in bidirectional connectivity. Using novel DCM leave-one-out cross-validation, we show that the most consistent out-of-sample predictions of the state of consciousness come from a key set of frontoparietal connections. This finding also generalises to unseen data collected during post-anaesthetic recovery. Our findings provide new, computational evidence for the importance of the posterior hot zone in explaining the loss of consciousness, highlighting also the distinct role of frontoparietal connectivity in underpinning conscious responsiveness, and consequently, suggest a dissociation between the mechanisms most prominently associated with explaining the contrast between conscious awareness and unconsciousness, and those maintaining consciousness. HighlightsO_LIModelling shows that connectivity within hot zone tracks change of conscious state C_LIO_LISeparately, frontoparietal connections support maintenance of conscious state C_LIO_LIStrength of frontoparietal connections predicts conscious state in unseen data C_LIO_LIBoth parietal hot zone and frontoparietal connectivity important for consciousness C_LI FundingThis work was supported by the UK Engineering and Physical Sciences Research Council (EP/P033199/1), Belgian National Funds for Scientific Research (FRS-FNRS), the University and University Hospital of Liege, the Fund Generet, the King Baudouin Foundation, the AstraZeneca Foundation, the European Unions Horizon 2020 Framework Programme for Research and Innovation under the Specific Grant Agreement No. 945539 (Human Brain Project SGA3), DOCMA project (EU-H2020-MSCA-RISE-778234), the BIAL Foundation, the European Space Agency (ESA) and the Belgian Federal Science Policy Office (BELSPO) in the framework of the PRODEX Programme, the Center-TBI project (FP7-HEALTH-602150), the Public Utility Foundation Universite Europeenne du Travail, "Fondazione Europea di Ricerca Biomedica", the Mind Science Foundation, the European Commission, and the Special Research Fund of Ghent University. O.G. is research associate and S.L. is research director at the F.R.S-FNRS. Declaration of interestNone. Significance StatementVarious connectivity studies have suggested multiple network-level mechanisms driving changes in the state of consciousness, such as the posterior hot zone, frontal-, and large-scale frontoparietal networks. Here, we computationally evaluate evidence for these mechanisms using dynamic causal modeling for resting EEG recorded before and during propofol-anaesthesia, and demonstrate that, particularly, connectivity in the posterior hot zone is impaired during propofol-induced unconsciousness. With a robust cross-validation paradigm, we show that connectivity in the large-scale frontoparietal networks can consistently predict the state of consciousness and further generalise these findings to an unseen state of recovery. These results suggest a dissociation between the mechanisms most prominently associated with explaining the contrast between conscious awareness and unconsciousness, and those maintaining consciousness.

neuroscience↗

bioRxiv2020

Aging Reduces EEG Markers of Recognition Despite Intact Performance: Implications for Forensic Memory Detection

ERP-based forensic memory detection is based on the logic that guilty suspects will hold incriminating knowledge about crimes they have committed, and therefore should show parietal ERP positivities related to recognition when presented with reminders of their crimes. We predicted that such forensic memory detection might however be inaccurate in older adults, because of changes to recognition-related brain activity that occurs with aging. We measured both ERPs and EEG oscillations associated with episodic old/new recognition and forensic memory detection in 30 younger (age < 30) and 30 older (age > 65) adults. EEG oscillations were included as a complementary measure which is less sensitive to temporal variability and component overlap than ERPs. In line with predictions, recognition-related parietal ERP positivities were significantly reduced in the older compared to younger group in both tasks, despite highly similar behavioural performance. We also observed ageing-related reductions in oscillatory markers of recognition in the forensic memory detection test, while the oscillatory effects associated with episodic recognition were similar across age groups. This pattern of results suggests that while both forensic memory detection and episodic recognition are accompanied by ageing-induced reductions in parietal ERP positivities, these reductions may be caused by non-overlapping mechanisms across the two tasks. Our findings suggest that EEG-based forensic memory detection tests are invalid in older populations, limiting their practical applications.

neuroscience↗

bioRxiv2020

Strategic and non-strategic semantic expectations hierarchically modulate neural processing

Perception is facilitated by a hierarchy of expectations generated from context and prior knowledge. In auditory processing, violations of local (within-trial) expectations elicit a mismatch negativity, while violations of global (across-trial) expectations elicit a later positive component (P300). This result is taken as evidence of prediction errors ascending through the expectation hierarchy. However, in language comprehension, there is no evidence that violations of semantic expectations across local-global levels similarly elicit a sequence of hierarchical error signals - thus drawing into question the putative link between event-related potentials and prediction errors. We investigated the neural basis of such hierarchical expectations of semantics in a word-pair priming paradigm. By manipulating the overall proportion of related or unrelated word-pairs across the task, we created two global contexts that differentially encouraged strategic use of primes. Across two experiments, we replicated behavioural evidence of greater priming in the high validity context, reflecting strategic expectations of upcoming targets based on global context. In our pre-registered EEG analyses, we observed a local prediction error ERP effect (i.e. semantic priming) approximately 250ms post-target, which, in exploratory analyses, was followed 100ms later by a signal that interacted with the global context. However, the later effect behaved in an apredictive manner - i.e. was most extreme for fulfilled expectations, rather than violations. Our results are consistent with interpretations of early ERPs as reflections of prediction error and later ERPs as processes related to conscious access and in support of task demands. Significance statementSemantic expectations have been associated with the ERP N400 component, which is modulated by semantic prediction errors across levels of the hierarchy. However, there is no evidence of a two-stage profile that reflects violations of semantic expectations at a single level of the hierarchy, such as the MMN and P3b observed in the local-global paradigm, which are elicited by violations of local and global expectations, respectively. In the present study, we provided evidence of an early ERP effect that reflects violations of local semantic expectations, followed by an apredictive signal that interacted with the global context. Thus, these results support the notion of early ERPs as prediction errors and later ERPs reflecting conscious access and strategic use of context.

neuroscience↗

bioRxiv2020

Event-related potentials reflect prediction errors and pop-out during comprehension of degraded speech

Comprehension of degraded speech requires higher-order expectations informed by prior-knowledge. Accurate top-down expectations of incoming degraded speech cause a subjective semantic "pop-out" or conscious breakthrough experience. Indeed, the same stimulus can be perceived as meaningless when no expectations are made in advance. We investigated the ERP correlates of these top-down expectations, their error signals, and the subjective pop-out experience in healthy participants. We manipulated expectations in a word-pair priming noise-vocoded speech task and investigated the role of top-down expectation with a between-groups attention manipulation. Consistent with the role of expectations in comprehension, repetition priming significantly enhanced perceptual intelligibility of the noise-vocoded degraded targets for attentive participants. An early ERP was larger for mismatched (i.e. unexpected) targets than matched targets, indicative of an initial error signal not reliant on top-down expectations. Subsequently, a P3a-like ERP was larger to matched targets than mismatched targets only for attending participants - i.e. a pop-out effect. Rather than relying on complex post hoc interactions between prediction error and precision to explain this apredictive pattern, we consider our data to be consistent with prediction error minimisation accounts for early stages of processing followed by Global Neuronal Workspace-like breakthrough and processing in service of task goals.

neuroscience↗

bioRxiv2020

Sedation modulates fronto-temporal predictive coding circuits and the double surprise acceleration effect

Two important theories in cognitive neuroscience are predictive coding and the global workspace theory. A key research task is to understand how these two theories relate to one another, and particularly, how the brain transitions from a predictive early state to the eventual engagement of a brain-scale state (the global workspace). To address this question, we present a source-localisation of EEG responses evoked by the local-global task - an experimental paradigm that engages a predictive hierarchy, which encompasses the global workspace. The results of our source reconstruction suggest three-phases of processing. The first phase involves the sensory (here auditory) regions of the superior temporal lobe and predicts sensory regularities over a short timeframe (as per the local effect). The third phase is brain-scale, involving inferior frontal, as well as inferior and superior parietal regions; consistent with a global neuronal workspace (as per the global effect). Crucially, our analysis suggests that there is an intermediate (second) phase, involving modulatory interactions between inferior frontal and superior temporal regions. Furthermore, sedation with propofol reduces modulatory interactions in the second phase. This selective effect is consistent with a predictive coding explanation of sedation, with propofol acting on descending predictions of the precision of prediction errors; thereby constraining access to the global neuronal workspace.

neuroscience↗

bioRxiv2020

Modelling the Replay of Dynamic Memories from Cortical Alpha Oscillations with the Sync-Fire / deSync Model.

We here propose a neural network model to explore how neural oscillations might regulate the replay of memory traces. We simulate the encoding and retrieval of a series of events, where temporal sequences are uniquely identifiable by analysing population activity, as several recent EEG/MEG studies have shown. Our model comprises three parts, each considering distinct hypotheses. A cortical region actively represents sequences through the disruption of an intrinsically generated alpha rhythm, where a desynchronisation marks information-rich operations as the literature predicts. A binding region converts each event into a discrete index, enabling repetitions through a sparse encoding of events. We also instantiate a temporal region, where an oscillatory "ticking-clock" made up of hierarchical synfire chains discretely indexes a moment in time. By encoding the absolute timing between events, we show how one can use cortical desynchronisations to dynamically detect unique temporal signatures as they are replayed in the brain.

neuroscience↗

bioRxiv2018

Countering Cross-Individual Variance in Event Related Potentials with Functional Profiling

In this study, a simple method called the Weight Template (WT) is proposed for classifying brain responses of individuals into deceiving and non-deceiving. The performance of our method was evaluated on a number of identity deception data sets and on artificial EEG data sets. A comparison was made with a standard method used to measure P3 presence, called Peak-to-Peak. In the real experimental data, the WT showed higher performance in terms of sensitivity and specificity. In the artificial EEG data, in ERPs with low Signal-to-Noise Ratio (SNR), the WT was more resistant to noise and provided more accurate measures. HighlightsO_LIWe propose a method for classifying ERPs of the P3 Concealed Information Tests. C_LIO_LIThe new method is based on computing a weighted template (WT) for each individual. C_LIO_LIThe WT is used to characterize the shape of each individuals P3. C_LIO_LIThe performance of the WT was compared with the standard Peak-to-Peak method. C_LIO_LIThe WT showed higher performance in terms of sensitivity and specificity. C_LI

bioengineering↗

bioRxiv2018

Understanding visual attention with RAGNAROC: A Reflexive Attention Gradient through Neural AttRactOr Competition

A quintessential challenge for any perceptual system is the need to focus on task-relevant information without being blindsided by unexpected, yet important information. The human visual system incorporates several solutions to this challenge, one of which is a reflexive covert attention system that is rapidly responsive to both the physical salience and the task-relevance of new information. This paper presents a model that simulates behavioral and neural correlates of reflexive attention as the product of brief neural attractor states that are formed across the visual hierarchy when attention is engaged. Such attractors emerge from an attentional gradient distributed over a population of topographically organized neurons and serve to focus processing at one or more locations in the visual field, while inhibiting the processing of lower priority information. The model moves towards a resolution of key debates about the nature of reflexive attention, such as whether it is parallel or serial, and whether suppression effects are distributed in a spatial surround, or selectively at the location of distractors. Most importantly, the model develops a framework for understanding the neural mechanisms of visual attention as a spatiotopic decision process within a hierarchy and links them to observable correlates such as accuracy, reaction time, and the N2pc and PD components of the EEG. This last contribution is the most crucial for repairing the disconnect that exists between our understanding of behavioral and neural correlates of attention.

neuroscience↗

bioRxiv2018

Speed of time-compressed forward replay flexibly changes in human episodic memory

Remembering information from continuous past episodes is a complex task. On the one hand, we must be able to recall events in a highly accurate way that often includes exact timing; on the other hand, we can ignore irrelevant details and skip to events of interest. We here track continuous episodes, consisting of different sub-events, as they are recalled from memory. In behavioral and MEG data, we show that memory replay is temporally compressed and proceeds in a forward direction. Neural replay is characterized by the reinstatement of temporal patterns from encoding. These fragments of activity reappear on a compressed timescale. Herein, the replay of sub-events takes longer than the transition from one sub-event to another. This identifies episodic memory replay as a dynamic process in which participants replay fragments of fine-grained temporal patterns and are able to skip flexibly across sub-events.

neuroscience↗

bioRxiv2018

Not so proportional after all?

BackgroundThe proportional recovery rule asserts that most stroke survivors recover a fixed proportion of lost function. Reports that the rule can be used to predict recovery, extraordinarily accurately, are rapidly accumulating. Here, we show that the rule may not be as powerful as it seems.\n\nMethodsWe provide a formal analysis of the relationship between baseline scores (X), outcomes (Y) and recovery (Y-X), to highlight the shortcomings of the proportional recovery rule, and illustrate those problems with simulations in which synthetic recovery data are derived from different types of recovery processes.\n\nFindingsWhen the correlation between baseline scores and recovery is stronger than that between baselines scores and outcomes, the former can create an inflated impression of how predictable outcomes really are given baseline scores. This often happens when outcomes are less variable than baseline scores, as is common in empirical studies of recovery after stroke. Moreover, we cannot use the results of these correlations to distinguish proportional recovery from recovery which is either not consistently proportional, or not proportional at all.\n\nInterpretationAnalyses relating baseline scores to subsequent change are a minefield: our formal analysis applies as consistently outside the area of stroke as it does within it. One implication of our analysis is that the proportional recovery rule is not as predictive of real recovery after stroke as recent empirical studies suggest. Another is that different analytical methods will be required to ascertain whether recovery is even proportional at all.

neuroscience↗