Biology subjects

Ferez, M.

Publications and source records attributed to Ferez, M..

5 recordsLinked to original sources

bioRxiv2026

Signal space beamforming for gain- and geometry-independent interference suppression in wearable MEG

Optically pumped magnetometers (OPMs) for wearable magnetoencephalography (MEG) offer substantial flexibility compared to cryogenic MEG, but they also introduce new challenges related to environmental noise and movement artefacts. State-of-the-art denoising techniques such as signal space separation require not only dense OPM arrays but also the fine calibration of sensor gain and geometry. This may complicate their use in complex experimental situations involving uncooperative patients or subjects such as newborns or fetuses, where OPM positioning may be unstable or plain unknown. To address this limitation, we introduce signal space beamforming (SSB), a version of beamforming applied to sensor signals and designed to suppress interferences independently of sensor gain and geometry. We show that SSB operates via a trade-off between noise suppression and neural signal preservation that is controlled by a single soft-threshold parameter, which we calibrated using phantom measurements. We then validated the effectiveness of SSB across several datasets. Using interictal OPM-MEG recordings in epileptic patients, SSB successfully cleaned signals while preserving epileptiform discharges. Moving onto cutting-edge early neurodevelopmental OPM-MEG recordings, SSB allowed to recover auditory evoked responses in newborns and fetuses similar to previous findings but with more streamlined preprocessing and higher response amplitude in the case of the fetal data. We contend that SSB provides a pragmatic solution to exploit OPM-MEG data recorded in challenging conditions where geometry-dependent methods cannot be used, opening new frontiers for pioneering clinical and fundamental applications of the OPM technology.

neuroscience↗

bioRxiv2025

Fetal magnetoencephalography based on optically pumped magnetometers

The fetus in the third trimester of gestation has already the remarkable capacity to process external sensory information in utero. So far, investigations of fetal brain responses to sensory information have mostly relied on cryogenic magnetoencephalography (MEG), which is suitable to record fetal brain activity and is not much affected by layers of maternal tissues. Nevertheless, this solution is extremely expensive and limited to a couple of laboratories worldwide. In this work, we took advantage of the next generation cryogenic-free MEG, that is MEG based on optically pumped magnetometers (OPM), to develop a system that could record both fetal and newborn brain responses to auditory stimulation in a longitudinal design. Twenty-one pregnant women in their late third trimester of gestation (35-40 weeks of gestational age) were exposed to sequences of 500 Hz tones. Fetal brain activity was recorded using a wearable belt equipped with OPM sensors arranged on the womens abdomen based on fetal head position. Results revealed that fetal OPM-MEG successfully recorded significant evoked brain responses to auditory stimuli that peaked ~300 ms post-stimulus at the group level. A similar auditory paradigm was performed with on-scalp OPM-MEG in 14 one-month-old infants, with 9 participants common to both timepoints. Infant responses showed a significant latency decrease compared to the fetal ones in terms of magnetometers; a decrease that did not reach significance level for virtual gradiometers. This work demonstrates the ability of OPM-MEG to non-invasively record fetal brain responses to external sensory stimuli. It paves the way for a wider use of fetal MEG to investigate fetal cognition and positions OPM-MEG as the most promising lifespan-compliant solution for monitoring early brain development.

neuroscience↗

bioRxiv2024

A Novel, Robust, and Portable Platform for Magnetoencephalography using Optically Pumped Magnetometers

Magnetoencephalography (MEG) measures brain function via assessment of magnetic fields generated by neural currents. Conventional MEG uses superconducting sensors, which place significant limitations on performance, practicality, and deployment; however, the field has been revolutionised in recent years by the introduction of optically-pumped-magnetometers (OPMs). OPMs enable measurement of the MEG signal without cryogenics, and consequently the conception of OPM-MEG systems which ostensibly allow increased sensitivity and resolution, lifespan compliance, free subject movement, and lower cost. However, OPM-MEG remains in its infancy with limitations on both sensor and system design. Here, we report a new OPM-MEG design with miniaturised and integrated electronic control, a high level of portability, and improved sensor dynamic range (arguably the biggest limitation of existing instrumentation). We show that this system produces equivalent measures when compared to an established instrument; specifically, when measuring task-induced beta-band, gamma-band and evoked neuro-electrical responses, source localisations from the two systems were highly comparable and temporal correlation was >0.7 at the individual level and >0.9 for groups. Using an electromagnetic phantom, we demonstrate improved dynamic range by running the system in background fields up to 8 nT. We show that the system is effective in gathering data during free movement (including a sitting-to-standing paradigm) and that it is compatible with simultaneous electroencephalography (EEG - the clinical standard). Finally, we demonstrate portability by moving the system between two laboratories. Overall, our new system is shown to be a significant step forward for OPM-MEG technology and offers an attractive platform for next generation functional medical imaging.

neuroscience↗

bioRxiv2023

Extending the applicability of optically pumped magnetoencephalography toward early human life

Characterizing the early development of the human brain is critical from both fundamental and clinical perspectives. However, existing neuroimaging techniques are either not well suited to infants or have limited spatial or temporal resolution. The advent of optically pumped magnetometers (OPMs) has revolutionized magnetoencephalography (MEG) by enabling wearable and thus more naturalistic recordings while maintaining excellent sensitivity and spatiotemporal resolution. Nevertheless, its adaptation to studying neural activity in infancy poses several challenges. In this work, we present an original close-to-scalp OPM-MEG setup that successfully recorded brain responses to sounds in newborns. We exposed one-month-old infants to continuous streams of tones and observed significant evoked responses, which peaked [~]250 ms poststimulus at bilateral auditory cortices. When tones were presented at a steady fixed pace with an oddball tone every fourth tone, significant neural responses were found both at the frequency of the standard tones (3 Hz) and of the oddball tones (0.75 Hz). The latter reflects the ability of the newborn brain to detect auditory change and synchronize to regular auditory patterns. Additional analyses support the added value of triaxial OPMs to increase the number of channels on small heads. Finally, OPM-MEG responses were validated with those obtained from the same participants using an adult-sized cryogenic MEG. This study demonstrates the applicability of OPM-MEG to study early postnatal periods; a crucial step towards future OPM investigations of typical and pathological early brain development.

neuroscience↗

bioRxiv2019

Estimates of cortical column orientation improveMEG source inversion

Determining the anatomical source of brain activity non-invasively measured from EEG or MEG sensors is challenging. In order to simplify the source localization problem, many techniques introduce the assumption that current sources lie on the cortical surface. Another common assumption is that this current flow is orthogonal to the cortical surface, thereby approximating the orientation of cortical columns. However, it is not clear which cortical surface to use to define the current source locations, and normal vectors computed from a single cortical surface may not be the best approximation to the orientation of cortical columns. We compared three different surface location priors and five different approaches for estimating dipole vector orientation, both in simulations and visual and motor evoked MEG responses. We show that models with source locations on the white matter surface and using methods based on establishing correspondences between white matter and pial cortical surfaces dramatically outperform models with source locations on the pial or combined pial/white surfaces and which use methods based on the geometry of a single cortical surface in fitting evoked visual and motor responses. These methods can be easily implemented and adopted in most M/EEG analysis pipelines, with the potential to significantly improve source localization of evoked responses.

neuroscience↗