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Spatially precise activation of the mouse cochlea with a multi-channel hybrid cochlear implant.
(Journal of Neural Engineering, 2025-05-06) Azees, Ajmal A; Thompson, Alex C; Ruther, Patrick; Ajay, Elise A; Zhou, Jenny; Aregueta Robles, Ulises A; Garrett, David J; Quigley, Anita; Fallon, James B; Richardson, Rachael T
Cochlear implants are among the few clinical interventions for people with severe or profound hearing loss. However, current spread during monopolar electrical stimulation results in poor spectral resolution, prompting the exploration of optical stimulation as an alternative approach. Enabled by introducing light-sensitive ion channels into auditory neurons (optogenetics), optical stimulation has been shown to activate a more discrete neural area with minimal overlap between each frequency channel during simultaneous stimulation. However, the utility of optogenetic approaches is uncertain due to the low fidelity of responses to light and high-power requirements compared to electrical stimulation.Hybrid stimulation, combining sub-threshold electrical and optical pulses, has been shown to improve fidelity and use less light, but the impact on spread of activation and channel summation using a translatable, multi-channel hybrid implant is unknown. This study examined these factors during single channel and simultaneous multi-channel hybrid stimulation in transgenic mice expressing the ChR2/H134R opsin. Acutely deafened mice were implanted with a hybrid cochlear array containing alternating light emitting diodes and platinum electrode rings. Spiking activity in the inferior colliculus was recorded during electrical-only or hybrid stimulation in which optical and electrical stimuli were both at sub-threshold intensities. Thresholds, spread of activation, and threshold shifts during simultaneous hybrid stimulation were compared to electrical-only stimulation.The electrical current required to reach activation threshold during hybrid stimulation was reduced by 7.3 dB compared to electrical-only stimulation (< 0.001). The activation width measured at two levels of discrimination above threshold and channel summation during simultaneous hybrid stimulation were significantly lower compared to electrical-only stimulation (< 0.05), but there was no spatial advantage of hybrid stimulation at higher electrical stimulation levels.Reduced channel interaction would facilitate multi-channel simultaneous stimulation, thereby enhancing the perception of temporal fine structure which is crucial for music and speech in noise.
The fNIRS glossary project: a consensus-based resource for functional near-infrared spectroscopy terminology.
(Neurophotonics, 2025-04-18) Stute, Katharina; Gossé, Louisa K; Montero-Hernandez, Samuel; Perkins, Guy A; Yücel, Meryem A; Cutini, Simone; Durduran, Turgut; Ehlis, Ann-Christine; Ferrari, Marco; Gervain, Judit; Mesquita, Rickson C; Orihuela-Espina, Felipe; Quaresima, Valentina; Scholkmann, Felix; Tachtsidis, Ilias; Torricelli, Alessandro; Wabnitz, Heidrun; Yodh, Arjun G; Carp, Stefan A; Dehghani, Hamid; Fang, Qianqian; Fantini, Sergio; Hoshi, Yoko; Niu, Haijing; Obrig, Hellmuth; Klein, Franziska; Artemenko, Christina; Bajracharya, Aahana; Barth, Beatrix; Bartkowski, Christian; Borot, Lénac; Bulgarelli, Chiara; Busch, David R; Chojak, Malgorzata; DeFreitas, Jason M; Diprossimo, Laura; Dresler, Thomas; Eken, Aykut; Elsherif, Mahmoud M; Emberson, Lauren L; Exner, Anna; Ferdous, Talukdar Raian; Fiske, Abigail; Forbes, Samuel H; Gemignani, Jessica; Gerloff, Christian; Guérin, Ségolène M R; Guevara, Edgar; Hamilton, Antonia F de C; Hadi Hosseini, S M; Jain, Divya; Kerr-German, Anastasia N; Kong, Haiyan; Kroczek, Agnes; Longhurst, Jason K; Lührs, Michael; MacLennan, Rob J; Mehler, David M A; Meidenbauer, Kimberly L; Moreau, David; Mutlu, Murat C; Orti, Renato; Paranawithana, Ishara; Pinti, Paola; Jounghani, Ali Rahimpour; Reindl, Vanessa; Ross, Nicholas A; Sanchez-Alonso, Sara; Seidel-Marzi, Oliver; Shukla, Mohinish; Usama, Syed A; Talati, Musa; Vergotte, Grégoire; Atif Yaqub, M; Yu, Chia-Chuan; Zainodini, Hanieh
A shared understanding of terminology is essential for clear scientific communication and minimizing misconceptions. This is particularly challenging in rapidly expanding, interdisciplinary domains that utilize functional near-infrared spectroscopy (fNIRS), where researchers come from diverse backgrounds and apply their expertise in fields such as engineering, neuroscience, and psychology.
Estimating sensor-space EEG connectivity PART 2: Identifying optimal artifact reduction techniques for functional connectivity in real data.
(Clinical Neurophysiology, 2025-04-08) Miljevic, Aleksandra; Murphy, Oscar W; Fitzgerald, Paul B; Bailey, Neil W
Electroencephalography (EEG) can be used to assess functional brain connectivity (FC). However, there is considerable variability in the methods used for FC measurement across different studies, which may contribute to heterogeneity in research outcomes. We aimed to assess how different EEG pre-processing steps impact EEG-FC measurement when applied to real EEG data.
Estimating sensor-space EEG connectivity PART 1: Identifying best performing methods for functional connectivity in simulated data.
(Clinical Neurophysiology, 2025-04-08) Miljevic, Aleksandra; Murphy, Oscar W; Fitzgerald, Paul B; Bailey, Neil W
Functional brain connectivity (FC) can be estimated using electroencephalography (EEG). However, there is considerable variability across studies in the FC measures used and in data (pre-)processing methods, leading to difficulties comparing and amalgamating results between studies. Thus, standardisation of EEG (pre-)processing for the measurement and reporting of FC is needed.We aimed to assess differences in FC estimates produced by different settings across multiple EEG pre-processing steps, (including re-referencing and epoching) to validate a reliable methodological pipeline for assessing EEG-FC in simulated EEG data.
Ensemble responses of auditory midbrain neurons in the cat to speech stimuli at different signal-to-noise ratios
(Hearing Research, 2024-12-03) Anu Sabu; Dexter Irvine; David B Grayden; James Fallon
Originally reserved for those who are profoundly deaf, cochlear implantation is now common for people with partial hearing loss, particularly when combined with a hearing aid. This combined intervention enhances speech comprehension and sound quality when compared to electrical stimulation alone, particularly in noisy environments, but the physiological basis for the benefits is not well understood. Our long-term aim is to elucidate the underlying physiological mechanisms of this improvement, and as a first step in this process, we have investigated in normal hearing cats, the degree to which the patterns of neural activity evoked in the inferior colliculus (IC) by speech sounds in various levels of noise allows discrimination between those sounds. Neuronal responses were recorded simultaneously from 32 sites across the tonotopic axis of the IC in anaesthetised normal hearing cats (n = 7). Speech sounds were presented at 20, 40 and 60 dB SPL in quiet and with increasing levels of additive noise (signal-to-noise ratios (SNRs) –20, –15, –10, –5, 0, +5, +10, +15, +20 dB). Neural discrimination was assessed using a Euclidean measure of distance between neural responses, resulting in a function reflecting speech sound differentiation across various SNRs. Responses of IC neurons reliably encoded the speech stimuli when presented in quiet, with optimal performance when an analysis bin-width of 5–10 ms was used. Discrimination thresholds did not depend on stimulus level and were best for shorter analysis binwidths. This study sheds light on how the auditory midbrain represents speech sounds and provides baseline data with which responses to electro-acoustic speech sounds in partially deafened animals can be compared.