István Ulbert

István Ulbert
Hungarian Academy of Sciences | HAS · Institute of Cognitive Neuroscience and Psychology

MSc, MD, DSc

About

278
Publications
29,686
Reads
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10,792
Citations
Additional affiliations
January 2017 - present
Hungarian Academy of Sciences
Position
  • Group Leader
December 2014 - present
Pázmány Péter Catholic University
Position
  • Professor (Full)
January 2014 - December 2016
Hungarian Academy of Sciences
Position
  • Managing Director

Publications

Publications (278)
Article
Full-text available
Knowledge about the activity of single neurons is essential in understanding the mechanisms of synchrony generation, and particularly interesting if related to pathological conditions. The generation of interictal spikes—the hypersynchronous events between seizures—is linked to hyperexcitability and to bursting behaviour of neurons in animal models...
Article
The paper describes the development of a reusable electrode system for non-invasive brain–computer interface application with signal quality comparable to that of conventional wet Ag/AgCl electrodes. The innovative electrode system consists of a polyvinyl alcohol–glycerol–NaCl contact hydrogel and a 3D-printed, silver-coated polylactic acid electro...
Article
Full-text available
Episodic learning and memory retrieval are dependent on hippocampal theta oscillation, thought to rely on the GABAergic network of the medial septum (MS). To test how this network achieves theta synchrony, we recorded MS neurons and hippocampal local field potential simultaneously in anesthetized and awake mice and rats. We show that MS pacemakers...
Article
Full-text available
The meaning behind neural single unit activity has constantly been a challenge, so it will persist in the foreseeable future. As one of the most sourced strategies, detecting neural activity in high-resolution neural sensor recordings and then attributing them to their corresponding source neurons correctly, namely the process of spike sorting, has...
Preprint
Full-text available
Sleep EEG reflects voltage differences relative to a reference, while its spectrum reflects its composition of various frequencies. In contrast, the envelope of the sleep EEG reflects the instantaneous amplitude of oscillations, while its spectrum reflects the rhythmicity of the occurrence of these oscillations. The sleep EEG spectrum is known to r...
Preprint
Objective:Describing intracortical laminar organization of high frequency oscillations (HFOs).Methods:We recorded potential gradients with laminar microelectrode arrays (LME) for current source density (CSD) and multi-unit activity (MUA) analysis of interictal discharges (IID) and HFOs in the neocortex and mesial temporal lobe of focal epilepsy pat...
Article
Despite advantage of neuroimaging measures in translational research frameworks, less is known about the psychometric properties thereof, especially in middle-late adolescents. Earlier, we examined evidence of convergent and incremental validity of reward anticipation and response event-related potentials (ERPs) and here we examined, in the same sa...
Article
Full-text available
Sleep EEG reflects voltage differences relative to a reference, while its spectrum reflects its composition of various frequencies. In contrast, the envelope of the sleep EEG reflects the instantaneous amplitude of oscillations, while its spectrum reflects the rhythmicity of the occurrence of these oscillations. The sleep EEG spectrum is known to r...
Article
Full-text available
Inhibitory neurons innervating the perisomatic region of cortical excitatory principal cells are known to control the emergence of several physiological and pathological synchronous events, including epileptic interictal spikes. In humans, little is known about their role in synchrony generation, although their changes in epilepsy have been thoroug...
Preprint
Full-text available
Sleep EEG reflects instantaneous voltage differences relative to a reference, while its spectrum reflects the degree to which it is comprised of oscillations at various frequencies. In contrast, the envelope of the sleep EEG reflects the instantaneous amplitude of oscillations at specific frequencies, and its spectrum reflects the rhythmicity of th...
Conference Paper
Full-text available
In this paper, we investigate the long-term adhesion strength and barrier property of our recently proposed encapsulation stack that includes PDMS-Parylene C and PECVD interlayers (SiO2 and SiC) for adhesion improvement. To evaluate the adhesion strength of our proposed stack, the sample preparation consisted in depositing approximately 25 nm of Si...
Preprint
Full-text available
Cortical dynamics obey a 1/f power law, exhibiting an exponential decay of spectral power with increasing frequency. The slope and offset of this 1/f decay reflect the timescale and magnitude of aperiodic neural activity, respectively. These properties are tightly linked to cellular and circuit mechanisms (e.g. excitation:inhibition balance, firing...
Article
Full-text available
Publicly available neural recordings obtained with high spatial resolution are scarce. Here, we present an electrophysiological dataset recorded from the neocortex of twenty rats anesthetized with ketamine/xylazine. The wideband, spontaneous recordings were acquired with a single-shank silicon-based probe having 128 densely-packed recording sites a...
Article
Objective: The growing number of recording sites of silicon-based probes means that an increasing amount of neural cell activities can be recorded simultaneously, facilitating the investigation of underlying complex neural dynamics. In order to overcome the challenges generated by the increasing number of channels, highly automated signal processi...
Article
Despite ongoing advances in our understanding of local single-cellular and network-level activity of neuronal populations in the human brain, extraordinarily little is known about their “intermediate” microscale local circuit dynamics. Here, we utilized ultra-high-density microelectrode arrays and a rare opportunity to perform intracranial recordin...
Article
Full-text available
Sleep spindles are functionally important NREM sleep EEG oscillations which are generated in thalamocortical, corticothalamic and possibly cortico-cortical circuits. Previous hypotheses suggested that slow and fast spindles or spindles with various spatial extent may be generated in different circuits with various cortical laminar innervation patte...
Article
Full-text available
In neuroscience the use of a microelectrode array allows the detection of neuroelectric signals with high temporal resolution in a confined space within the tissue, while two-photon laser scanning microscopy provides high spatial resolution in a wide region of interest. The combination of these two techniques promises better understanding of the op...
Preprint
Full-text available
Episodic learning and memory retrieval are critically dependent on a hippocampal 4-12 Hz oscillatory 'clock' signal, the theta oscillation. This clock is largely externally paced, by a network of GABAergic neurons in the medial septum (MS). Theoretical studies suggested a range of hypotheses how this network may achieve theta synchrony; however, ex...
Article
Full-text available
Multisite, silicon-based probes are widely used tools to record the electrical activity of neuronal populations. Several physical features of these devices are designed to improve their recording performance. Here, our goal was to investigate whether the position of recording sites on the silicon shank might affect the quality of the recorded neura...
Article
Objective The goal of this study was to define the pathology and anesthesia dependency of single pulse electrical stimulation (SPES) dependent high-frequency oscillations (HFOs, ripples, fast ripples) in the hippocampal formation. Methods Laminar profile of electrically evoked short latency (<100 ms) high-frequency oscillations (80−500 Hz) was exa...
Article
Adolescence is a developmental period characterized by heightened reward sensitivity which, in turn, confers risk for pertinent negative outcomes, underscoring the need to better understand biological bases and behavioral correlates of reward responsiveness during this developmental phase. Our goals in the current study were to examine, in a sample...
Conference Paper
Full-text available
Eyetracking opens new possibilities for people with physical disabilities, enabling them to explore new ways of communication and interaction with their environment. However, this field of assistive technology is not available to everyone in need and still faces substantial obstacles: high-cost devices for use in real-world environments, difficulty...
Chapter
Full-text available
Classification of electroencephalography (EEG) signals is a fundamental issue of Brain Computer Interface (BCI) systems, and deep learning techniques are still under investigation although they are dominant in other fields like computer vision and natural language processing. In this paper, we introduce the chessboard image transformation method in...
Article
Full-text available
Broadband high-frequency activity (BHA; 70 to 150 Hz), also known as “high gamma,” a key analytic signal in human intracranial (electrocorticographic) recordings, is often assumed to reflect local neural firing [multiunit activity (MUA)]. As the precise physiological substrates of BHA are unknown, this assumption remains controversial. Our analysis...
Preprint
Full-text available
Objective: Multisite, silicon-based probes are widely used tools to record the electrical activity of neuronal populations. Several physical features of these devices (e.g. shank thickness, tip geometry) are designed to improve their recording performance. Here, our goal was to investigate whether the position of recording sites on the silicon shan...
Article
Background Mindset and communication barriers may hinder the acceptance of bariatric surgery (BS) by the eligible patient population. Objectives To improve the understanding of expectations, opinions, emotions and attitudes toward weight-loss among patients with obesity. Setting Switzerland, Germany, Austria. Methods Survey data collected from B...
Article
Full-text available
Spiking activity of individual neurons can be separated from the acquired multi-unit activity with spike sorting methods. Processing the recorded high-dimensional neural data can take a large amount of time when performed on general-purpose computers. Methods: In this paper, an FPGA- based real-time spike sorting system is presented which takes i...
Article
Full-text available
Decades of research support the idea that associations between a conditioned stimulus (CS) and an unconditioned stimulus (US) are encoded in the lateral amygdala (LA) during fear learning. However, direct proof for the sources of CS and US information is lacking. Definitive evidence of the LA as the primary site for cue association is also missing....
Article
Full-text available
The use of SU-8 material in the production of neural sensors has grown recently. Despite its widespread application, a detailed systematic quantitative analysis concerning its biocompatibility in the central nervous system is lacking. In this immunohistochemical study, we quantified the neuronal preservation and the severity of astrogliosis around...
Article
Full-text available
The alpha rhythm is the longest-studied brain oscillation and has been theorized to play a key role in cognition. Still, its physiology is poorly understood. In this study, we used microelectrodes and macroelectrodes in surgical epilepsy patients to measure the intracortical and thalamic generators of the alpha rhythm during quiet wakefulness. We f...
Article
Full-text available
Objective: The extraction and identification of single-unit activities in intracortically recorded electric signals have a key role in basic neuroscience, but also in applied fields, like in the development of high-accuracy brain-computer interfaces. The purpose of this paper is to present our current results on the detection, classification and p...
Article
Key points: Initiation of pathological synchronous events such as epileptic spikes and seizures is linked to the hyperexcitability of the neuronal network both in humans and animals. Here we show that epileptiform interictal-like spikes and seizures emerged in human neocortical slices by blocking GABAA receptors, following the disappearance of the...
Conference Paper
Full-text available
Here we show, that based on parallel multichannel extracellular and single channel intracellular potential recordings, it is possible the reconstruct the spatio-temporal distribution of membrane potential with the spatial resolution of the extracellular recordings in single neurons. Moreover we show, that reconstruction of membrane potential made p...
Article
Full-text available
The simultaneous utilization of electrophysiological recordings and two-photon imaging allows the observation of neural activity in a high temporal and spatial resolution at the same time. The three dimensional monitoring of morphological features near the microelectrode array makes the observation more precise and complex. In vitro experiments wer...
Article
We investigated the functional network reorganization caused by low-frequency electrical stimulation (LFES) of human brain cortical surface. Intracranial EEG data from subdural grid positions were analyzed in 16 pre-surgery epileptic patients. LFES was performed by injecting current pulses (10 mA, 0.2 ms pulse width, 0.5 Hz, 25 trials) into all...
Article
Aims In this study, we introduce an edge-type laminar silicon probe suitable for improved cell accessibility during in vitro brain slice recordings. With protruding contact sites, the spiky probe provides high signal yield and quality while approaching cells located deeper in the tissue. Methods. The spiky probe comprises an angled shank carrying 3...
Article
Background The local cortical activation-inhibition sequence underlying electrically evoked cortico-cortical potentials (CCEPs) is little known in humans. Our aim was to study these physiological mechanisms in drug-resistant epileptic patients implanted with subdural electrodes. Materials and methods To reveal the effect of cortical electrical sti...
Article
Full-text available
Background Sleep spindles are involved in memory consolidation and other cognitive functions. Numerous automated methods for detection of spindles have been proposed; most of these rely on spectral analysis in some form. However, none of these approaches are ideal, and novel approaches to the problem could provide additional insights. New method H...
Preprint
Full-text available
Sleep spindles are generated in thalamocortical, corticothalamic and possibly cortico-cortical circuits. Previous hypotheses suggested that slow and fast spindles or spindles with various spatial extent may be generated in different circuits with various cortical laminar innervation patterns. We used NREM sleep EEG data recorded from four human epi...
Article
Full-text available
Softening neural implants that change their elastic modulus under physiological conditions are promising candidates to mitigate neuroinflammatory response due to the reduced mechanical mismatch between the artificial interface and the brain tissue. Intracortical neural probes have been used to demonstrate the viability of this material engineering...
Preprint
Full-text available
Broadband High-frequency Activity (BHA; 70-150 Hz), also known as "high gamma," a key analytic signal in human intracranial recordings is often assumed to reflect local neural firing (multiunit activity; MUA). Accordingly, BHA has been used to study neuronal population responses in auditory (1,2), visual (3,4), language (5), mnemonic processes (6-9...
Article
Full-text available
Neural probes designed for extracellular recording of brain electrical activity are traditionally implanted with an insertion speed between 1 µm/s and 1 mm/s into the brain tissue. Although the physical effects of insertion speed on the tissue are well studied, there is a lack of research investigating how the quality of the acquired electrophysiol...