Biology subjects

Rhodes, E.

Publications and source records attributed to Rhodes, E..

6 recordsLinked to original sources

bioRxiv2026

Artefact-free EEG during temporal interference stimulation reveals phase-specific modulation of the human visual cortex

Background: Temporal interference (TI) stimulation applies kHz electric fields whose envelope is modulated at a difference frequency ({Delta}f), allowing non-invasive deep-brain targeting. Measuring the neural response during stimulation with EEG is essential for establishing mechanisms and for closed-loop control. However, non-linearities in the recording chain mix the kHz carriers, producing an artefact at exactly {Delta}f. Objectives: To establish a method for recording EEG during TI without the {Delta}f artefact, and to test whether TI modulates neural activity at {Delta}f. Methods: A front-end analogue low-pass filter (7th order; 90 Hz cut-off; [≥]130 dB attenuation at 1 kHz) was bench-tested. In 22 healthy participants, residual artefact was assessed per recording with a two-stage detection pipeline in stimulation-only blocks. TI targeted the right primary visual cortex at 10 or 15.5 Hz, in-phase or anti-phase with multi-frequency photic stimulation (4.5, 10, 15.5 Hz), during a choice reaction time task. Results: The filter suppressed the {Delta}f artefact below the noise floor on a resistive load. In vivo, residual artefact was confirmed in two participants and could not be excluded in two more; all four were excluded from EEG analyses. Steady-state visual evoked potential (SSVEP) amplitude at 11, 14.5 and 15.5 Hz predicted faster responses. In-phase 15.5 Hz TI increased SSVEP amplitude at 14.5 and 15.5 Hz and shortened response times relative to both sham and anti-phase TI, which did not differ from sham. Conclusions: With front-end filtering and per-recording verification, EEG can measure TI neuromodulation during stimulation and at {Delta}f, revealing phase-specific modulation of visual entrainment linked to behaviour.

neuroscience↗

bioRxiv2023

Just a phase? Causal probing reveals spurious phasic dependence of sensory perception

For over a decade, electrophysiological studies have reported correlations between sensory perception and the phase of spontaneous pre-stimulus brain oscillations. To date, these findings have been interpreted as evidence that the brain uses neural oscillations to sample and predict upcoming stimuli. Yet, evidence from simulations have shown that analysis artefacts could also lead to spurious pre-stimulus oscillations that appear to predict future brain responses. To address this discrepancy, we conducted an experiment in which visual stimuli were presented timed to specific phases of spontaneous alpha and theta oscillations. This allowed us to causally probe the role of ongoing neural activity in visual processing independent of the stimulus-evoked dynamics. Our findings did not support a causal link between spontaneous alpha / theta rhythms and behaviour. However, spurious correlations between theta phase and behaviour emerged offline using gold-standard acausal time-frequency analyses. These findings demonstrate that care should be taken when inferring causal relationships between neural activity and behaviour using acausal analyses. HIGHLIGHTSO_LIWe causally probed the role of spontaneous EEG rhythms in visual attention via phase-locking. C_LIO_LITheta phase predicted behaviour offline, but cues presented in real-time with theta had no effect on behaviour. C_LIO_LISpurious theta rhythmic sampling is an artefact of the evoked potential and acausal filtering. C_LIO_LIecHT accurately computes the phase in real-time and mitigates erroneous phase-behaviour correlations. C_LI

neuroscience↗

bioRxiv2023

The neuron mixer and its impact on human brain dynamics

A signal mixer made of a transistor or a diode facilitates rich computation, which has been the building block of modern telecommunications. The mixing produces new signals at the sum and difference frequencies of the input, thereby enabling powerful operations such as frequency conversion (aka heterodyning), phase detection, and multiplexing. Here, we report that a neural cell is also a signal mixer. We found through ex-vivo and in-vivo whole-cell measurements that neurons mix exogenous (controlled) and endogenous (spontaneous) subthreshold membrane potential oscillations, producing new oscillation frequencies. We show, using pharmacological manipulation, that the neural mixing originates in the voltage-gated ion channels. Furthermore, we demonstrate that the neural mixing dynamic is evident in human brain activity and is associated with cognitive functions. We found that the human electroencephalogram (EEG) displays distinct clusters of local and inter-region mixing interactions. By quantifying the strength of these interactions before a task, we show that converting the salient posterior alpha-beta oscillations into gamma-band oscillations regulates the visual attention state. Neural circuit oscillations have been observed in nearly every cognitive domain and species, and abnormal spectra of neural oscillations have been found in almost all brain disorders. Signal mixing enables individual neurons to actively sculpt the spectrum of their circuit oscillations and utilize them for computational operations, which have only been seen in modern telecommunication until now.

neuroscience↗

bioRxiv2022

Perfect Timing: Effects of Auditory Stimulation on Alpha Oscillations During Wakefulness and the Transition to Sleep are Phase-dependent in Humans

Alpha oscillations play a vital role in managing the brains resources, inhibiting neural activity as a function of their phase and amplitude, and are changed in many brain disorders. Developing minimally invasive tools to modulate alpha activity and identifying the parameters that determine its response to exogenous modulators, is essential for the implementation of focussed interventions. We introduce Alpha Closed-Loop Auditory Stimulation (CLAS) as an EEG-based method to augment and investigate these brain rhythms in humans with specificity and selectivity, using targeted auditory stimulation. Across three independent studies, we demonstrate that CLAS alters alpha power, frequency, and connectivity in a phase, amplitude and topography-dependent manner. Using a single-pulse-CLAS evoked potentials approach we show that the effects of auditory stimuli on alpha oscillations and resulting evoked potentials can be explained within the theoretical framework of oscillator theory and a phase-reset mechanism. Finally, we demonstrate the functional relevance of our approach by showing that CLAS modulates sleep onset dynamics in an alpha phase-dependent manner.

neuroscience↗

bioRxiv2022

Non-invasive temporal interference electrical stimulation of the human hippocampus

Deep brain stimulation (DBS) via implanted electrodes is used worldwide to treat patients with severe neurological and psychiatric disorders however its invasiveness precludes widespread clinical use and deployment in research. Temporal interference (TI) is a strategy for non-invasive steerable DBS using multiple kHz-range electric fields with a difference frequency within the range of neural activity. Here we report the validation of the non-invasive DBS concept in humans. We used electric field modelling and measurements in a human cadaver to verify that the locus of the transcranial TI stimulation can be steerably focused in the hippocampus with minimal exposure to the overlying cortex. We then used functional magnetic resonance imaging (fMRI) and behaviour experiments to show that TI stimulation can focally modulate hippocampal activity and enhance the accuracy of episodic memories in healthy humans. Our results demonstrate targeted, non-invasive electrical stimulation of deep structures in the human brain.

neuroscience↗

bioRxiv2020

Non-invasive Amelioration of Essential Tremor via Phase-Locked Disruption of its Temporal Coherence

Aberrant neural oscillations hallmark numerous brain disorders. Here, we first report a method to track the phase of neural oscillations in real-time via endpoint-corrected Hilbert transform (ecHT) that mitigates the characteristic Gibbs distortion. We then used ecHT to show that the aberrant neural oscillation that hallmarks essential tremor (ET) syndrome, the most common adult movement disorder, can be noninvasively suppressed via electrical stimulation of the cerebellum phase-locked to the tremor. The tremor suppression is sustained after the end of the stimulation and can be phenomenologically predicted. Finally, using feature-based statistical-learning and neurophysiological-modelling we show that the suppression of ET is mechanistically attributed to a disruption of the temporal coherence of the oscillation via perturbation of the tremor generating a cascade of synchronous activity in the olivocerebellar loop. The suppression of aberrant neural oscillation via phase-locked driven disruption of temporal coherence may represent a powerful neuromodulatory strategy to treat brain disorders.

neuroscience↗