Exploring the impact and influence of melanin on frequency-domain near-infrared spectroscopy measurements.

Significance: Near-infrared spectroscopy (NIRS) is a non-invasive optical method that measures changes in hemoglobin concentration and oxygenation. The measured light intensity is susceptible to reduced signal quality due to the presence of melanin.

Aim: We quantify the influence of melanin concentration on NIRS measurements taken with a frequency-domain near-infrared spectroscopy system using 690 and 830 nm.

Cell-specific effects of temporal interference stimulation on cortical function.

Temporal interference (TI) stimulation is a popular non-invasive neurostimulation technique that utilizes the following salient neural behavior: pure sinusoid (generated in off-target brain regions) appears to cause no stimulation, whereas modulated sinusoid (generated in target brain regions) does. To understand its effects and mechanisms, we examine responses of different cell types, excitatory pyramidal (Pyr) and inhibitory parvalbumin-expressing (PV) neurons, to pure and modulated sinusoids, in intact network as well as in isolation. In intact network, we present data showing that PV neurons are much less likely than Pyr neurons to exhibit TI stimulation.

Effect of electric field direction on neuronal activity: an ex-vivo study.

The effect of electrical stimulation on neurons depends on the spatiotemporal properties of the applied electric field as well as on the biophysical properties of the neural tissue, which includes geometric and electrical characteristics of the cells, and the neural circuit dynamics. In this work, we characterize the effect of electric field direction on neural response in cortical layers. This can, for instance, enable more efficient (e.

EEG Source Imaging of Infarct Core and Penumbra for Ischemic Stroke Patients.

A quantitative method of analyzing EEG signals after stroke onset can help monitor disease progression and tailor treatments. In this work, we present an EEG-based imaging algorithm to estimate the location and size of the stroke infarct core and penumbra tissues. Building on recent advancements in localizing neural silences, we develop an algorithm that utilizes known spectral properties of the infarct core and penumbra to separately localize them.

Scaling of Algorithmic Bias in Pulse Oximetry with Signal-to-Noise Ratio.

Recent work has noted a skin-color bias in existing pulse oximetry systems in their estimation of arterial oxygen saturation. Frequently, the algorithm used by these systems estimate a "ratio-of-ratios", called the "R-value", on their way to estimating the oxygen saturation. In this work, we focus on an "SNR-related" bias that is due to noise in measurements.

A Spatial-Temporal Graph Attention Network for Automated Detection and Width Estimation of Cortical Spreading Depression Using Scalp EEG.

We present an end-to-end Spatial-Temporal Graph Attention Network (STGAT) for non-invasive detection and width estimation of Cortical Spreading Depressions (CSDs) on scalp electroencephalography (EEG). Our algorithm, that we refer to as CSD Spatial-temporal graph attention network or CSD-STGAT, is trained and tested on simulated CSDs with varying width and speed ranges. Using high-density EEG, CSD-STGAT achieves less than 10.

Noninvasive and reliable automated detection of spreading depolarization in severe traumatic brain injury using scalp EEG.

Background: Spreading depolarizations (SDs) are a biomarker and a potentially treatable mechanism of worsening brain injury after traumatic brain injury (TBI). Noninvasive detection of SDs could transform critical care for brain injury patients but has remained elusive. Current methods to detect SDs are based on invasive intracranial recordings with limited spatial coverage.

A model of neurovascular coupling and its application to cortical spreading depolarization.

Cortical spreading depolarization (CSD) is a neuropathological condition involving propagating waves of neuronal silence, and is related to multiple diseases, such as migraine aura, traumatic brain injury (TBI), stroke, and cardiac arrest, as well as poor outcome of patients. While CSDs of different severity share similar roots on the ion exchange level, they can lead to different vascular responses (namely spreading hyperemia and spreading ischemia). In this paper, we propose a mathematical model relating neuronal activities to predict vascular changes as measured with near-infrared spectroscopy (NIRS) and fMRI recordings, and apply it to the extreme case of CSD, where sustained near-complete neuronal depolarization is seen.

Diffuse optical tomography spatial prior for EEG source localization in human visual cortex.

Electroencephalography (EEG) and diffuse optical tomography (DOT) are imaging methods which are widely used for neuroimaging. While the temporal resolution of EEG is high, the spatial resolution is typically limited. DOT, on the other hand, has high spatial resolution, but the temporal resolution is inherently limited by the slow hemodynamics it measures.

PATHFINDER: Designing Stimulus for Neuromodulation Through Data-Driven Inverse Estimation of Non-Linear Functions.

Objective: Using data-driven methods to design stimuli (e.g., electrical currents) which evoke desired neural responses in different neuron-types for applications in treating neural disorders.

Focused Epicranial Brain Stimulation by Spatial Sculpting of Pulsed Electric Fields Using High Density Electrode Arrays.

Transcranial electrical neuromodulation of the central nervous system is used as a non-invasive method to induce neural and behavioral responses, yet targeted non-invasive electrical stimulation of the brain with high spatial resolution remains elusive. This work demonstrates a focused, steerable, high-density epicranial current stimulation (HD-ECS) approach to evoke neural activity. Custom-designed high-density (HD) flexible surface electrode arrays are employed to apply high-resolution pulsed electric currents through skull to achieve localized stimulation of the intact mouse brain.

Building a culture of responsible neurotech: Neuroethics as socio-technical challenges.

Scientists around the globe are joining the race to achieve engineering feats to read, write, modulate, and interface with the human brain in a broadening continuum of invasive to non-invasive ways. The expansive implications of neurotechnology for our conception of health, mind, decision-making, and behavior has raised social and ethical considerations that are inextricable from neurotechnological progress. We propose "socio-technical" challenges as a framing to integrate neuroethics into the engineering process.

HingePlace: Focused transcranial electrical current stimulation that allows subthreshold fields outside the stimulation target.

Transcranial Electrical Stimulation (TES) is a promising tool for treating many neurological disorders, but it classically results in diffused stimulation. Many optimization algorithms have been proposed for focusing TES, commonly by creating multi-electrode arrangements and choosing current amplitudes such that the resulting current fields in the brain are focused in the target region, and are as small as possible outside the target region. Consequently, it is likely that such optimization does not harness the non-linear nature of neural dynamics, particularly their thresholding phenomenon, i.

Projections and the Potential Societal Impact of the Future of Neurotechnologies.

Traditionally, recording from and stimulating the brain with high spatial and temporal resolution required invasive means. However, recently, the technical capabilities of less invasive and non-invasive neuro-interfacing technology have been dramatically improving, and laboratories and funders aim to further improve these capabilities. These technologies can facilitate functions such as multi-person communication, mood regulation and memory recall.

Abnormalities in cortical pattern of coherence in migraine detected using ultra high-density EEG.

Individuals with migraine generally experience photophobia and/or phonophobia during and between migraine attacks. Many different mechanisms have been postulated to explain these migraine phenomena including abnormal patterns of connectivity across the cortex. The results, however, remain contradictory and there is no clear consensus on the nature of the cortical abnormalities in migraine.

Neural silences can be localized rapidly using noninvasive scalp EEG.

A rapid and cost-effective noninvasive tool to detect and characterize neural silences can be of important benefit in diagnosing and treating many disorders. We propose an algorithm, SilenceMap, for uncovering the absence of electrophysiological signals, or neural silences, using noninvasive scalp electroencephalography (EEG) signals. By accounting for the contributions of different sources to the power of the recorded signals, and using a hemispheric baseline approach and a convex spectral clustering framework, SilenceMap permits rapid detection and localization of regions of silence in the brain using a relatively small amount of EEG data.

Quantifying a frequency modulation response biomarker in responsive neurostimulation.

Responsive neurostimulation (RNS) is an effective treatment for controlling seizures in patients with drug-resistant focal epilepsy who are not suitable candidates for resection surgery. A lack of tools for detecting and characterizing potential response biomarkers, however, contributes to a limited understanding of mechanisms by which RNS improves seizure control. We developed a method to quantify ictal frequency modulation, previously identified as a biomarker of clinical responsiveness to RNS.

Effect of skull thickness and conductivity on current propagation for noninvasively injected currents.

When currents are injected into the scalp, e.g. during transcranial current stimulation, the resulting currents generated in the brain are substantially affected by the changes in conductivity and geometry of intermediate tissue.

Enhanced spatiotemporal resolution imaging of neuronal activity using joint electroencephalography and diffuse optical tomography.

Electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) are both commonly used methodologies for neuronal source reconstruction. While EEG has high temporal resolution (millisecond-scale), its spatial resolution is on the order of centimeters. On the other hand, in comparison to EEG, fNIRS, or diffuse optical tomography (DOT), when used for source reconstruction, can achieve relatively high spatial resolution (millimeter-scale), but its temporal resolution is poor because the hemodynamics that it measures evolve on the order of several seconds.

Current Conceptual Understanding of the Epileptogenic Network From Stereoelectroencephalography-Based Connectivity Inferences.

Localization of the epileptogenic zone (EZ) is crucial in the surgical treatment of focal epilepsy. Recently, EEG studies have revealed that the EZ exhibits abnormal connectivity, which has led investigators to now consider connectivity as a biomarker to localize the EZ. Further, abnormal connectivity of the EZ may provide an explanation for the impact of focal epilepsy on more widespread brain networks involved in typical cognition and development.

Novel Electrodes for Reliable EEG Recordings on Coarse and Curly Hair.

EEG is a powerful and affordable brain sensing and imaging tool used extensively for the diagnosis of neurological disorders (e.g. epilepsy), brain computer interfacing, and basic neuroscience.

Hydrophilic Conductive Sponge Sensors for Fast Setup, Low Impedance Bio-potential Measurements.

Low electrode-skin impedance can be achieved if the interface has an electrolytic medium that allows the movement of ions across the interface. Maintaining good physical contact of the sensor with the skin is imperative. We propose a novel hydrophilic conductive sponge interface that encapsulates both of these fundamental concepts into an effective physical realization.

Differentiation of Types of Visual Agnosia Using EEG.

Visual recognition deficits are the hallmark symptom of visual agnosia, a neuropsychological disorder typically associated with damage to the visual system. Most research into visual agnosia focuses on characterizing the deficits through detailed behavioral testing, and structural and functional brain scans are used to determine the spatial extent of any cortical damage. Although the hierarchical nature of the visual system leads to clear predictions about the temporal dynamics of cortical deficits, there has been little research on the use of neuroimaging methods with high temporal resolution to characterize the temporal profile of agnosia deficits.

Cortical Hyper-Excitability in Migraine in Response to Chromatic Patterns.

Objective: Individuals with migraine exhibit heightened sensitivity to visual input that continues beyond their migraine episodes. However, the contribution of color to visual sensitivity, and how it relates to neural activity, has largely been unexplored in these individuals.

Background: Previously, it has been shown that, in non-migraine individuals, patterns with greater chromaticity separation evoked greater cortical activity, regardless of hue, even when colors were isoluminant.

STIMULUS: Noninvasive Dynamic Patterns of Neurostimulation Using Spatio-Temporal Interference.

Objective: This paper obtains strategies that can achieve spatially precise noninvasive deep brain stimulation using electrical currents.

Methods: We provide the Spatio-Temporal Interference-based stiMULation focUsing Strategy (STIMULUS) that generates rich patterns of spatiotemporally interfering currents to stimulate precisely and deep inside the brain. To calibrate and compare the accuracy of stimulation using different techniques, we utilize computational Hodgkin-Huxley-type models for neurons and a model of current dispersion in the head.