Biology subjects

Umbach, G.

Publications and source records attributed to Umbach, G..

6 recordsLinked to original sources

bioRxiv2025

Electrocorticographic Detection of Speech Networks in Glioma-infiltrated Cortex

Direct cortical stimulation (DCS) is the clinical gold standard for identifying functional cortex in the human brain, which is essential for the safe removal of brain lesions. Defining the electro-physiological properties of DCS- positive cortical regions may facilitate the identification of critical language regions, thereby permitting safe glioma resections in communities without access. Leveraging a multicenter electrophysiologic dataset of DCS- positive language regions spatially matched with subdural arrays, we analyzed regions identified as functionally critical (DCS+) versus functionally non-critical (DCS-) during intraoperative language mapping. In IDH-mutant gliomas, DCS+ regions exhibited significantly greater speech-related neural activity and enhanced encoding and decoding of linguistic and semantic features. We demonstrate that resting-state classifiers distinguish DCS+ from DCS- regions in IDH-mutant tumors. Task-based and resting-state electrophysiologic distinctions were pathology-specific and not present in IDH-wildtype glioblastomas. These findings may accelerate DCS mapping by guiding surgeons to priority regions, improving efficiency, and patient outcomes.

neuroscience↗

bioRxiv2025

Aperiodic neural dynamics define a novel signature of glioma-induced excitation-inhibition dysregulation

Diffuse gliomas remodel neuronal circuits with prognostic and therapeutic significance for patients. Electrophysiologic measures of cortical excitability hold promise for monitoring disease progression and evaluating therapeutic responses. The power law exponent (aperiodic slope) reflects the balance between excitatory and inhibitory activity within neuronal networks, a critical aspect of normal brain function often disrupted in neurological conditions. Despite its potential, the significance of the aperiodic slope in glioma-infiltrated tissue and its underlying cellular processes has not been fully investigated. Here, we integrate multi-modal electrophysiological analysis with transcriptomic profiling to analyze the aperiodic slope in both normal and glioma-infiltrated cortex. We determine that glioma infiltration induces a flattening of the aperiodic slope, indicating a shift toward excitation dominance that varies according to tumor subtype and correlates with impairments in semantic naming. Single-nucleus RNA sequencing revealed that cortical regions with flat aperiodic slope exhibit transcriptional programs enriched in glutamatergic signaling, membrane depolarization, and excitatory synaptic transmission. The aperiodic slope responds to pharmacologically induced changes in cortical inhibition during propofol administration, a GABAA agonist. Our results establish the aperiodic slope as a robust biomarker of glioma-associated excitation-inhibition imbalance, with potential applications in tumor classification and treatment monitoring.

cancer biology↗

bioRxiv2021

Boundary cells in the representation of episodes in the human hippocampus

The representation of episodes is a fundamental requirement for forming episodic memories, but the specific electrophysiological mechanisms supporting episode construction in the human hippocampus remain unknown. Experiments in rodent models indicate that a population of neurons sensitive to edges of an environment, termed border or boundary neurons in spatial navigation, fulfills a role analogous to episode demarcation. We hypothesized that such boundary neurons could be identified in the human mesial temporal lobe, with firing rates sensitive specifically to the beginning and end of mnemonically-relevant episodes in the free recall task. Using a generalized linear model to control for factors such as encoding success and item onset times along with other variables, we found 44 Boundary neurons out of a total 736 single neurons recorded across 27 subjects. We distinguish boundary neurons from a separate population of ramping neurons, which are time-sensitive neurons whose activity provides complementary but distinct information during episodic representation. We also describe evidence that the firing of boundary neurons within the preferred windows (at the beginning and end of episodes) is organized by hippocampal theta oscillations, using spike-field coherence metrics.

neuroscience↗

bioRxiv2021

Flexibility of Functional Neuronal Assemblies Supports Human Memory

Summary ParagraphEpisodic memories, or consciously accessible memories of unique events, represent a key aspect of human cognition. Evidence from rodent models suggests that the neural representation of these complex memories requires cooperative firing of groups of neurons on short time scales1, organized by gamma oscillations2, 3. These co-firing groups, termed "neuronal assemblies,"4 represent a fundamental neurophysiological unit supporting memory. Using microelectrode data from neurosurgical patients5, we identify neuronal assemblies in the human MTL and show that they exhibit consistent organization in their firing pattern based on gamma phase information. We connect these properties to memory performance across recording sessions. Finally, we describe how human neuronal assemblies flexibly adjust6-9 over longer time scales. Our findings provide key evidence linking assemblies to human episodic memory for the first time.

neuroscience↗

bioRxiv2020

Time cells in the human hippocampus and entorhinal cortex support episodic memory

The organization of temporal information is critical for the encoding and retrieval of episodic memories. In the rodent hippocampus and entorhinal cortex, recent evidence suggests that temporal information is encoded by a population of "time cells." We identify time cells in humans using intracranial microelectrode recordings obtained from 27 human epilepsy patients who performed an episodic memory task. We show that time cell activity predicts the temporal organization of episodic memories. A significant portion of these cells exhibits phase precession, a key phenomenon not previously seen in human recordings. These findings establish a cellular mechanism for the representation of temporal information in the human brain needed to form episodic memories.

neuroscience↗

bioRxiv2019

Intracranial EEG reveals bihemispheric parietal and extra parietal brain networks supporting mental arithmetic

Mathematical reasoning is central to everyday life. Lesion data and functional MRI studies suggest that even simple arithmetic involves the coordination of multiple spatially diverse brain regions, but to date, math processing has not been well characterized using direct brain recordings, especially outside of the parietal cortex. To address this, we utilized an unparalleled data set of 310 subjects implanted with intracranial electrodes to investigate the spatial and temporal dynamics of arithmetic reasoning. Our data support the importance of regions previously implicated in numerosity such as the superior parietal lobule and intraparietal sulcus. However, we also identify contributions to arithmetic processing from regions such as the entorhinal cortex and temporal pole. Using the excellent bihemispheric coverage afforded by our data set and the precise temporal resolution of intracranial recordings, we characterize in detail the spatial and temporal characteristics of an arithmetic processing network, quantifying subtle hemispheric differences for selected regions. We also examine how activity in these regions predicts arithmetic ability and look for gender differences in the pattern of network activation. Our findings further define the complex network of regions involved in human arithmetical reasoning.

neuroscience↗