Biology subjects

Stengel, C.

Publications and source records attributed to Stengel, C..

5 recordsLinked to original sources

bioRxiv2022

In vivo low-intensity magnetic pulses durably alter neocortical neuron excitability and spontaneous activity.

Magnetic brain stimulation is a promising treatment for neurological and psychiatric disorders. However, a better understanding of its effects at the individual neuron level is essential to improve its clinical application. We combined focal low-intensity repetitive transcranial magnetic stimulation (LI-rTMS) to the rat somatosensory cortex with intracellular recordings of subjacent pyramidal neurons in vivo. Continuous 10 Hz LI-rTMS reliably evoked firing at [~]4-5 Hz during the stimulation period and induced durable attenuation of synaptic activity and spontaneous firing in cortical neurons, through membrane hyperpolarization and a reduced intrinsic excitability. However, inducing firing in individual neurons by repeated intracellular current injection did not reproduce LI-rTMS effects on neuronal properties. These data provide novel understanding of mechanisms underlying magnetic brain stimulation showing that, in addition to inducing biochemical plasticity, even weak magnetic fields can activate neurons and enduringly modulate their excitability.

neuroscience↗

bioRxiv2021

Causal contributions of neural noise to left frontal networks subtending the modulation of conscious visual perception in the human brain

For several decades, the field of human neurophysiology has focused on the role played by cortical oscillations in enabling brain function underpinning behaviors. In parallel, a less visible but robust body of work on the stochastic resonance phenomenon has also theorized contributions of neural noise - hence more heterogeneous, complex and less predictable activity - in brain coding. The latter notion has received indirect causal support via improvements of visual function during non-regular or random brain stimulation patterns. Nonetheless, direct evidence demonstrating an impact of brain stimulation on direct measures of neural noise is still lacking. Here we evaluated the impact of three non frequency-specific TMS bursts, compared to a control pure high-beta TMS rhythm, delivered to the left FEF during a visual detection task, on the heterogeneity, predictability and complexity of ongoing brain activity recorded with scalp EEG. Our data showed surprisingly that the three non frequency-specific TMS patterns did not prevent a build-up of local high-beta activity. Nonetheless, they increased power across broader or in multiple frequency bands compared to control purely rhythmic high-beta bursts tested along. Importantly, non frequency-specific patterns enhanced signal entropy over multiple time-scales, suggesting higher complexity and an overall induction of higher levels of cortical noise than rhythmic TMS bursts. Our outcomes provide indirect evidence on a potential modulatory role played by sources of stochastic noise on brain oscillations and synchronization. Additionally, they pave the way towards the development of novel neurostimulation approaches to manipulate cortical sources of noise and further investigate their causal role in neural coding.

neuroscience↗

bioRxiv2019

Causal modulation of right fronto-parietal phase synchrony with Transcranial Magnetic Stimulation during a conscious visual detection task

Correlational evidence in non-human primates has reported evidence of increased frontoparietal high-beta band (22-30 Hz) synchrony during the endogenous allocation of visuospatial attention. But may the engagement of inter-regional synchrony at this specific frequency band provide the causal mechanism by which top-down processes are engaged and they facilitate visual perception in humans? Here we further analyzed electroencephalographic (EEG) signals from a group of healthy human participants who performed a conscious visual detection task, under the influence of brief rhythmic (30 Hz) or random bursts of Transcranial Magnetic Stimulation (TMS), with an identical number of pulses and duration, delivered to the right Frontal Eye Field (FEF) prior to the onset of a lateralized near-threshold target. We report increases of inter-regional synchronization in the high-beta band (25-35 Hz) between the electrode closest to the stimulated region (right FEF) and parietal leads, and increases of local inter-trial coherence in the same frequency band over parietal contacts, both driven by rhythmic but not random TMS patterns. Importantly, such increases were accompained by increases of visual sensitivity for left visual targets (contralateral to the stimulation) in the rhythmic but not the random TMS condition at the group level. These outcomes suggest that human high-beta synchrony between right frontal and parietal regions can be modulated non-invasively and that high-beta oscillatory activity across the right dorsal fronto-parietal network may contribute to the facilitation of conscious visual detection. Our study also supports future applications of non-invasive brain stimulation technologies for the manipulation of inter-regional synchrony, which could be administered to improve visual behaviors in healthy humans or neurological patients.

neuroscience↗

bioRxiv2019

Perturbation-based mapping of natural frequencies with direct intracranial stimulation of the human brain

Theoretical and experimental evidence suggest that the induction of oscillatory activity by an external rhythmic source on a specific brain area is maximally efficient if the input pattern matches its so-called natural frequency, defined as the predominant neural rhythm at which the activity of this area tends to fluctuate spontaneously. Based on this principle, single pulse Transcranial Magnetic Stimulation (TMS) coupled to scalp electroencephalography (EEG) has provided evidence of frequency-specific power increases within a unique natural frequency band, considered common to the whole lobe.\n\nIn an attempt to gain deeper insight into this phenomenon and set the basis for a finer-grained atlas of natural frequencies, here we analyzed intracranial EEG (iEEG) signals modulated by single pulses of direct electrical brain stimulation in human patients implanted with depth multielectrodes. Our analyses revealed changes in local EEG activity emerging from local oscillators and contributing to a complex distribution of frequency-specific natural rhythmic responses throughout cortical regions. Moreover, challenging the notion of natural oscillations featuring a predominant frequency band characteristic for an entire lobe, our data support a rich diversity of spectral fingerprints (narrowband, vs. broadband or multiband) with single or multiple frequency peaks, often encompassing contiguous frequency bands, operating at a very local scale.\n\nOur findings contribute novel insights on which specific brain areas could be more likely to be synchronized at a given frequencies band and their preferred coupling frequencies, features that could ultimately inform on their structural and functional organization. Our results may also increase our mechanistic understanding of invasive and noninvasive brain stimulation and promote further developments of these approaches for the manipulation of brain oscillations subtending normal and impaired cognition.

neuroscience↗

bioRxiv2019

Entrainment of local synchrony reveals a causal role for high-beta right frontal oscillations in human visual consciousness

Prior evidence supports the critical role of oscillatory activity in cognitive function, but are cerebral oscillations simply correlated or causally linked to specific aspects of visual cognition? Here, EEG signals were recorded on humans performing a conscious visual detection task, while they received brief rhythmic or random noninvasive stimulation patterns delivered to the right Frontal Eye Field prior to the onset of a lateralized target. Compared to random patterns, rhythmic high-beta patterns led to greater entrainment of local oscillations (i.e., increased power and phase alignment at the stimulation frequency), and to higher conscious detection of contralateral targets. When stimulation succeeded in enhancing visual detection, the magnitude of oscillation entrainment correlated with visual performance increases. Our study demonstrates a causal link between high-beta oscillatory activity in the Frontal Eye Field and conscious visual perception. Furthermore, it supports future applications of brain stimulation to manipulate local synchrony and improve or restore impaired visual behaviors.

neuroscience↗