Biology subjects

Barbeau, E. J.

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

3 recordsLinked to original sources

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.

neuroscience↗

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

neuroscience↗

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

neuroscience↗