Biology subjects

Barbeau, E. J.

Publications and source records attributed to Barbeau, E. J..

10 recordsLinked to original sources

bioRxiv2026

How aging reshapes implicit learning: behavioral and oscillatory evidence from an EEG-adapted Fast Mapping paradigm.

Most of everyday memory formation occurs without deliberate intent, yet the neural mechanisms supporting implicit encoding and their reorganization with age remain poorly understood. The present study investigated age-related changes in implicit learning using an EEG-adapted Fast Mapping paradigm (the Disjunctive Inference Implicit Learning Test, DIILT) in 31 younger and 35 older adults, paired with a comprehensive neuropsychological assessment and a one-month delayed recognition measure. Behaviorally, younger adults rapidly acquired novel implicit associations across the learning phase, whereas older adults showed persistent reliance on familiar items and limited improvement for novel associations. Critically, both groups successfully retained novel associations after one month, with implicitly learned associations showing greater long-term stability than explicitly encoded ones regardless of age. At the neural level, younger adults exhibited early posterior theta engagement for novel compared to familiar items, which disappeared by the end of learning, consistent with novelty-driven associative encoding. Older adults showed no such theta modulation for novel items, pointing to reorganization of the neural mechanisms supporting implicit encoding. Theta dynamics predicted immediate recognition in younger adults but not in older adults who rather showed theta association with processing speed, suggesting an age-related shift from memory-specific binding to domain-general cognitive resource allocation, consistent with neural maintenance frameworks of cognitive aging. These findings demonstrate that implicit encoding produces durable memory traces across the lifespan but relies on reorganized oscillatory dynamics in aging, with implications for understanding how cognitive aging reshapes everyday memory formation.

neuroscience↗

bioRxiv2026

A learning-evoked slow-oscillatory architecture paces population activity for offline reactivation across the human medial temporal lobe

Memory processing requires the coordinated engagement of neuronal populations across distributed brain networks and across time. How such coordination is organized in the human medial temporal lobe (MTL) remains unclear. Here, we show that MTL population activity is dynamically structured by a transient slow-oscillatory architecture that emerges during online learning to promote offline consolidation and later recall. Using intracranial recordings that combine single-neuron spiking activity and local field potentials in human participants, we find that mnemonic engagement evokes on-demand slow-oscillatory bursts in the hippocampus. These hippocampal bursts synchronize gamma-band patterns across MTL regions, defining discrete coordination events that pace cross-regional coactivity motifs during learning. These learning-time population motifs are then selectively reactivated during hippocampal ripples in post-learning rest, and the strength of their reactivation predicts subsequent recall accuracy. Together, these findings identify a multi-scale coordination mechanism that links distributed population activity across learning, consolidation, and recall in humans.

neuroscience↗

bioRxiv2025

A Reappraisal of the Role of the Mammillothalamic Tract in Memory Deficits Following Stroke in the Thalamus

The thalamus, traditionally viewed as a sensory relay station, is now recognized for its critical role in higher-order cognitive functions, including memory. While most research has focused on its distinct nuclei, the thalamus also contains crucial white matter tracts, such as the mammillothalamic tract (MTT), part of the Papez circuit. Despite its established role in memory, the MTT remains underappreciated in studies on the cognitive role of the thalamus, increasing the risk of misattributing memory functions to nearby thalamic nuclei. This study investigates the memory impact of thalamic strokes by considering disruption to the MTT. We examined 40 patients with chronic ischemic thalamic lesions and 45 healthy controls using neuropsychological assessments, focusing on the Free and Cued Selective Reminding Test (FCSRT) and high-resolution structural neuroimaging. Advanced imaging techniques, such as symptom mapping and disconnectome analyses, were employed to analyze the relationships between lesion sites, tract disconnections and cognitive outcomes. Additionally, the expression of calbindin-rich matrix cells and parvalbumin-rich core cells was examined to assess how the connectivity property of thalamic cells, and its disruption, can relate to cognitive deficits following a thalamic stroke. Patients with left-sided thalamic lesions, especially those involving the MTT, showed significant memory impairments. Symptom mapping identified a specific cluster of lesioned voxels in the left anterior-lateral thalamus, including the MTT, as being strongly associated with poorer memory performance. Disconnectome analysis confirmed that verbal memory deficits were associated with disruption of the MTT. Furthermore, a striking overlap was observed between the critical regions linked to memory deficits and calbindin-rich thalamic areas. However, this calbindin-rich region was also disrupted in patients without memory impairment, revealing that MTT disruption, and not lesions to this region, induced memory deficits in these patients. The identified FCSRT deficit cluster overlapped with brain regions consistently linked to memory processes following fMRI meta-analytic mapping of memory-related keywords. These findings challenge the traditional focus on thalamic nuclei and connector hubs, indicating a need to reappraise the importance of the MTT in memory impairment after a thalamic stroke. This study advocates for a shift in thalamic research, emphasizing the need to investigate tract-specific contributions and disruptions of the MTT but also of other tracts such as the interthalamic adhesion or amygdalo-fugal pathway, rather than holding only to a "nuclei-centric" view of the thalamus.

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bioRxiv2024

A large cohort study (n = 591) on the impact of the presence or absence of the interthalamic adhesion: cognitive, neuroimaging, and genetic results

Both thalami can be connected by an Interthalamic Adhesion (IA). The extent of its presence varies among individuals and remains poorly understood. This study examines the IAs prevalence, anatomical variations, genetic determinants, and cognitive associations. Data from 591 healthy subjects (25-35 years) from the Human Connectome Project were analyzed and grouped as monozygotic (MZ) twins, dizygotic (DZ) twins, non-twin siblings, and unrelated individuals. MRI was used to characterize the IA, while neuropsychological assessments and Freesurfer parcellations were used to assess cognition and anatomical differences between subjects with or without an IA. The IA was absent in 12.7% of subjects, more commonly in males (20.0%) than females (6.3%), with no significant differences in age, education, or cognition between those with and without an IA. IA absence was associated with increased cerebrospinal fluid volumes, enlarged third ventricles, and thinning in several cortical areas. Genetic analysis revealed a higher concordance of IA presence among MZ twins (96%) than in other groups, indicating a strong genetic influence. The remaining 4% discrepancy was observed in male pairs only. This study underscores the genetic basis of IA, highlighting sexual dimorphism and neuroanatomical differences associated with its absence, though it does not affect cognition in healthy individuals.

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bioRxiv2024

Factors behind poor cognitive outcome following a thalamic stroke

ObjectiveThalamic strokes produce a range of neurological, cognitive, and behavioral symptoms depending on the thalamic nuclei involved. While thalamic strokes are traditionally associated with severe cognitive deficits, recent studies suggest more modest impairments. This study aims to identify the factors that influence the severity of cognitive impairment following thalamic stroke. MethodsWe recruited 40 patients (median age 51) with chronic isolated thalamic stroke and 45 healthy subjects. All subjects underwent neuroimaging and neuropsychological testing. Cluster and principal component analyses were used to discriminate patients from healthy subjects based on cognitive performance. Disconnectome maps and cortical thickness were analyzed to understand the distant impact of thalamic strokes. ResultsTwo cognitive profiles emerged. Cluster 1 included mostly healthy subjects (n = 43) and patients with no or minor deficits (n = 20); Cluster 2 included patients (n = 19) and 2 healthy subjects with severe deficits of verbal memory, executive functions, and attention. Cluster 1 included all patients with right thalamic stroke. Cluster 2 included all patients with bilateral stroke or mammillothalamic tract disruption. Patients with left-sided stroke were equally divided between Cluster 1 and 2. Other significant differences included age, education, interthalamic adhesion disruption, lesion volume, and location. Disconnectome maps showed larger disruptions of the anterior thalamic projection in patients with left-sided stroke of Cluster 2. InterpretationContrary to common expectations, our findings indicate that many patients with thalamic stroke have relatively good cognitive outcomes. In contrast, we identified some of the factors behind poor outcomes that may help clinicians.

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bioRxiv2024

Exploring the impact of interthalamic adhesion on human cognition: insights from healthy subjects and thalamic stroke patients

Background and ObjectivesInterthalamic adhesion (IA), also known as the massa intermedia, is a structure that connects the median borders of both thalami across the third ventricle. Given it is difficult to identify on routine neuroimaging, its anatomical variants and function remain poorly studied. The main objective of this study was to clarify the role of IA on cognition. Our main hypothesis was that thalamus stroke patients with an IA would show better performance on neuropsychological tests than individuals without an IA through possible compensatory mechanisms. MethodsThe study comprised a group of healthy subjects and a cohort of patients with isolated thalamic strokes at the chronic stage. All participants underwent 3T research T1w and FLAIR MRI as well as a neuropsychological assessment. The presence or absence of an IA and type of IA anatomical variant were evaluated by two independent reviewers. Results42 healthy subjects (mean age= 49) and 40 patients (mean age= 51) were finally included. 76% of participants had an IA, with a higher prevalence among women (92%) than men (61%). The presence or absence of an IA did not effect the neuropsychological performance of healthy subjects nor did the type of IA variant. Across all the tests, patients with an IA (n = 18) showed the lowest BF10 (157) while those without an IA (n = 10) exhibited the highest BF10 (10648) when compared to healthy subjects using a Bayesian rmANOVA. More specifically, patients without an IA performed more poorly in the verbal memory or Stroop task versus healthy subjects than patients with an IA. This effect was not explained by age, laterality of the infarct, volume or, localization of the lesion. Patients with an IA and lesions extending into the IA presented a similar trend to non-IA subjects which could however be explained by a greater volume of lesions. DiscussionIA does not appear to have a major role in cognition for healthy subjects but could play a compensatory part in patients with thalamic lesions.

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bioRxiv2022

Independent component analysis reveals an early hippocampal recognition system using intracerebral evoked potentials in humans

The role of the hippocampal formation in memory recognition has been well studied in animals, with different pathways and structures linked to specific memory processes. In contrast, the hippocampus is commonly analyzed as a unique responsive area in most electrophysiological studies in humans, and the specific activity of its subfields remains unexplored. We combined intracerebral electroencephalogram recordings from epileptic patients with independent component analysis (ICA) during a memory recognition task involving the recognition of old and new images to disentangle the activities of multiple neuronal sources within the hippocampus. We identified two sources with different responses emerging from the hippocampus: a fast one (maximum at [~]250 ms) that could not be directly identified from raw recordings, and a later one, peaking at [~]400 ms. The earliest component was found in 12 out of 15 electrodes, with different amplitudes for old and new items in half of the electrodes. The latter component, identified in 13 out of 15 electrodes, had different delays for each condition, with a faster activation ([~]290 ms after stimulus onset) for recognized items. We hypothesize that both sources represent two steps of hippocampal memory recognition, the faster reflecting the input from other structures and the latter the hippocampal internal processing. Recognized images evoking early activations would facilitate neural computation in the hippocampus, accelerating memory retrieval of complementary information. Overall, our results suggest that hippocampal activity is composed by several sources, including an early system for memory recognition, that can be disentangled with ICA methods. SIGNIFICANCE STATEMENTIn the human memory circuit, the hippocampus is considered as a relatively late structure, associated to the retrieval of elaborated memories. In most electrophysiological studies, it is analyzed as a unique responsive area, and the specific activity of its subfields remains unexplored. In this work, we combined intracerebral recordings with independent component analysis to separate the electrophysiological activity from two different substructures of the hippocampus. We analyzed the responses of both sources in a memory task involving the recognition of old and new images. Our results revealed new hippocampal dynamics associated to different subfields, with memory recognition occurring much faster than previously reported. Importantly, we confirmed the potential of independent component analysis, which can be extended to other brain areas.

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bioRxiv2021

Local neuronal excitation and global inhibition during epileptic fast ripples in humans.

Understanding the neuronal basis of epileptiform activity is a major challenge in neurology. Interictal epileptiform discharges are associated with fast ripples (FRs, >200 Hz) in the local field potential (LFP) and are a promising marker of the epileptogenic zone. Here, by using a novel hybrid macro-micro depth electrode, combining classic depth recording of LFP and two or three tetrodes enabling up to 15 neurons in local circuits to be recorded simultaneously, we have characterized neuronal responses to FRs on the same hybrid and other electrodes targeting other brain regions. While FRs were associated with increased neuronal activity in local circuits only, they were followed by inhibition in large-scale networks. Neuronal responses to FRs were homogeneous in local networks but differed across brain areas. Similarly, post-FR inhibition varied across recording locations and subjects and was shorter than typical inter-FR intervals, suggesting that this inhibition is a fundamental refractory process for the networks. These findings demonstrate that FRs engage local and global networks and point to network features that pave the way for new diagnostic and therapeutic strategies.

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bioRxiv2020

Dynamic connectivity analyses of intracranial EEG during recognition memory reveal various large-scale functional networks

Recognition memory is the ability to recognize previously encountered events, objects, or people. It is characterized by its robustness and rapidness. Even this relatively simple ability requires the coordinated activity of a surprisingly large number of brain regions. These spatially distributed, but functionally linked regions are interconnected into large-scale networks. Understanding memory requires an examination of the involvement of these networks and the interactions between different regions while memory processes unfold. However, little is known about the dynamical organization of large-scale networks during the early phases of recognition memory. We recorded intracranial EEG, which affords high temporal and spatial resolution, while epileptic subjects performed a visual recognition memory task. We analyzed dynamic functional and effective connectivity as well as network properties. Various networks were identified, each with its specific characteristics regarding information flow (feedforward or feedback), dynamics, topology, and stability. The first network mainly involved the right visual ventral stream and bilateral frontal regions. It was characterized by early predominant feedforward activity, modular topology, and high stability. It was followed by the involvement of a second network, mainly in the left hemisphere, but notably also involving the right hippocampus, characterized by later feedback activity, integrated topology, and lower stability. The transition between networks was associated with a change in network topology. Overall, these results confirm that several large-scale brain networks, each with specific properties and temporal manifestation, are involved during recognition memory. Ultimately, understanding how the brain dynamically faces rapid changes in cognitive demand is vital to our comprehension of the neural basis of cognition. O_LIVarious dynamic large-scale networks support recognition memory. C_LIO_LIThe first is mostly feedforward and involves the right hemisphere and the bilateral frontal lobes. C_LIO_LIThe second is mostly feedback and includes left MTL regions and the right hippocampus. C_LIO_LIChanges in network topology accompany the switch between the networks. C_LI

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bioRxiv2020

Building memories on prior knowledge: behavioral and fMRI evidence of impairment in early Alzheimer's Disease

Impaired memory is a hallmark of prodromal Alzheimers Disease (AD). Prior knowledge associated with the memoranda has proved to have a powerful effect on memory in healthy subjects. Yet, barely nothing is known about its effect in early AD. We used functional MRI to ask whether prior knowledge enhanced memory encoding in early AD and whether the nature of prior knowledge mattered. Early AD patients and healthy controls underwent a task-based fMRI experiment, being scanned while learning face-scene associations. Famous faces carried Pre-Experimental Knowledge (PEK) while unknown faces repeatedly familiarized prior to learning carried Experimental Knowledge (EK). As expected, PEK increased subsequent memory in healthy elderly. However, patients did not benefit from PEK. Partly non-overlapping brain networks supported PEK vs. EK encoding in healthy controls. Patients displayed impaired activation in a right subhippocampal region where activity predicted successful associative memory formation of PEK stimuli. These findings call for a thorough consideration of how prior knowledge impacts learning and suggest a possible underestimation of the extent of associative memory impairment in early AD. HighlightsO_LILearning is impaired in prodromal AD, but we currently ignore whether prior knowledge available at encoding promotes learning in AD as it does in healthy controls. C_LIO_LIPatients with AD failed to benefit from pre-experimental prior knowledge (famous faces) by comparison with experimental knowledge (unknown but familiarized faces). C_LIO_LIfMRI responses at study revealed distinct networks underlying associative encoding for both pre-experimental and experimental knowledge. C_LIO_LIA subsequent memory effect found in control subjects for associations carrying pre-experimental knowledge in the right subhippocampal structures, including the perirhinal cortex, was absent in patients. C_LIO_LIPre-experimental knowledge-based associative encoding relies on brain regions specifically targeted by early tau pathology. C_LIO_LIUsing unfamiliar materials to probe memory in early AD might underestimate learning impairment. C_LI

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