Bionics Institute

There remain large variations in cochlear implant auditory-speech perception ability, which are poorly explained by patient history factors. This study aims to better understand how combinations of speech processing limitations, identified using psychophysical and functional brain imaging measures, are associated with long-term speech understanding outcomes of new cochlear implant recipients. Forty-three cochlear implant recipients (44 ears) were recruited to participate in a longitudinal study to evaluate limitations at various locations along the auditory processing pathway. At the periphery, intra-cochlear neural health was estimated using focused psychophysical thresholds. Higher-order across-electrode intensity discrimination ability was assessed using psychophysical "spectral tilt." At the cortical level, cross-modal activation of the auditory cortex was assessed using functional near-infrared spectroscopy. Speech understanding outcomes were evaluated in competing multi-talker babble noise at 1-year post-device switch-on. We found that greater abilities to discriminate smaller across-electrode stimulation intensities ( R2 = 0.138, p = 0.047) and smaller cross-modal activations of the auditory cortex ( R2 = 0.216, p = 0.01) were significantly associated with better speech understanding outcomes in cochlear implant recipients. Furthermore, both measures contributed significantly to better predict speech understanding outcomes in a multiple regression model (Adj R2 = 0.312, p = 0.009). The results suggest that recipient-specific psychophysical and functional brain imaging metrics contribute significantly toward individual differences in speech understanding outcomes. Different recipients can be affected by different limitations, which can be identified using these tests, and therefore lead to potential patient-specific methods to improve their speech understanding.

Improving diagnostic accuracy of obsessive-compulsive disorder (OCD) using models of brain imaging data is a key goal of the field, but this objective is challenging due to the limited size and phenotypic depth of clinical datasets. Leveraging the phenotypic diversity in large non-clinical datasets such as the UK Biobank (UKBB), offers a potential solution to this problem. Nevertheless, it remains unclear whether classification models trained on non-clinical populations will generalise to individuals with clinical OCD. This question is also relevant for the conceptualisation of OCD; specifically, whether the symptomology of OCD exists on a continuum from normal to pathological. Here, we examined a recently published "meta-matching" model trained on functional connectivity data from five large normative datasets (N = 45,507) to predict cognitive, health and demographic variables. Specifically, we tested whether this model could classify OCD status in three independent datasets (N = 345). We found that the model could identify out-of-sample OCD individuals. Notably, the most predictive functional connectivity features mapped onto known cortico-striatal abnormalities in OCD and correlated with genetic brain expression maps previously implicated in the disorder. Further, the meta-matching model relied upon estimates of cognitive functions, such as cognitive flexibility and inhibition, to successfully predict OCD. These findings suggest that variability in non-clinical brain and behavioural features can discriminate clinical OCD status. These results support a dimensional and transdiagnostic conceptualisation of the brain and behavioural basis of OCD, with implications for research approaches and treatment targets.

Conductive hydrogels have been increasingly designed as wearable strain sensors due to their significant potential in human motion monitoring and health detection applications. However, the integration of multiple desirable characteristics within a single hydrogel system remains challenging. Furthermore, environmental factors such as humidity and low temperatures often compromise hydrogel sensor functionality, substantially limiting their practical applications and value. In this study, we developed a mussel-inspired multifunctional CACa conductive hydrogel through in situ polymerization by incorporating polyacrylamide (PAM), tannic acid (TA), carboxymethyl cellulose (CMC), and aminated carbon nanotubes (NH2–CNTs) into a unified gel network. By optimizing the CMC mass fraction and subsequent cross-linking via calcium chloride (CaCl2) solution immersion, the resulting hydrogel demonstrates exceptional stretchability, self-adhesion, moisturizing/antifreezing capabilities, conductivity, and underwater adhesion. As a self-adhesive wearable strain sensor, CACa hydrogel can directly adhere to human skin without external assistance. It exhibits high sensitivity and rapid response to various physiological signals, including finger flexion, wrist rotation, elbow movement, and throat vibration during speech. Remarkably, this flexible electronic material maintains functionality even under subzero temperatures and aqueous environments. The hydrogel’s underwater adhesion enables effective motion signal detection and information transmission in submerged conditions. This work provides insights for developing advanced wearable sensors and underwater monitoring devices, significantly expanding the potential applications of multifunctional conductive hydrogels.

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. We simulated EEG-FC data where the 'ground truth' of the connections is known and compared estimates of FC from this ground truth data across multiple FC measures and variations in multiple pre-processing steps. Our results indicated that pre-processing steps that included segmenting the data into 40 or more epochs that were 6s or more in length provided the most accurate estimation of the simulated FC. With regards to the data re-referencing, the Reference Electrode Standardization Technique or the common average re-referencing appeared best when used in conjunction with imaginary coherence and weighted phase lag index metrics. However, the magnitude-squared coherence FC measure performed best with the Current Source Density reference free techniques. Our paper provides an evidence-base for the influence of referencing, epoch length and number, controls for volume conduction, and different FC metrics on EEG-FC measurement. Using this evidence, we present an initial and promising account of the best performing (pre-)processing choices for robust EEG-FC assessment.

Objective.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.Approach.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.Main results.The electrical current required to reach activation threshold during hybrid stimulation was reduced by 7.3 dB compared to electrical-only stimulation (p< 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 (p< 0.05), but there was no spatial advantage of hybrid stimulation at higher electrical stimulation levels.Significance.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.

Abstract Intracochlear electrodes in cochlear implants (CIs) offer a novel method for recording auditory brain activity without external EEG equipment, addressing challenges in pediatric CI users. This study tested the feasibility of recording electrically evoked cortical auditory evoked potential (eCAEPs) directly via the CI system. Twenty children and three adults with bilateral Advanced Bionics CIs participated. A brief electrical stimulus was delivered to one CI, while the contralateral CI recorded responses using a basal electrode referenced to the case. Each session included stimulus and non-stimulus sweeps, with averaging over 600 ms revealing clear eCAEP patterns. All participants exhibited obligatory P1, N1, and P2 peaks within a test duration of under five minutes. The method showed good test-retest repeatability and expected latency shifts occurred with stimulus level adjustments. Compared to scalp recorded EEG, intracochlear recordings produced significantly larger amplitudes with similar latencies. Early-implanted children displayed distinct eCAEP patterns, and better performing CI users had earlier P1 responses. This recording approach provides a robust, non-invasive tool for monitoring CI users, particularly young children, offering potential advancements in post-implantation assessment and intervention by eliminating external equipment while ensuring reliable recordings.

The cerebellar ataxias (CAs) are a heterogeneous group of disorders characterized by progressive incoordination. Seventeen repeat expansion (RE) loci have been identified as the primary genetic cause and account for >80% of genetic diagnoses. Despite this, diagnostic testing is limited and inefficient, often utilizing single gene assays. This study evaluates the effectiveness of long- and short-read sequencing as diagnostic tools for CA. We recruited 110 individuals (48 females, 62 males) with a clinical diagnosis of CA. Short-read genome sequencing (SR-GS) was performed to identify pathogenic RE and also non-RE variants in 356 genes associated with CA. Independently, long-read sequencing with adaptive sampling (LR-AS) was performed to identify pathogenic RE. SR-GS provided a genetic diagnosis for 38% of the cohort (40/110) including seven non-RE pathogenic variants. RE causes disease in 33 individuals, with the most common condition being SCA27B (n = 24). In comparison, LR-AS identified pathogenic RE in 29 individuals. RE identification for the two methods was concordant apart from four SCA27B cases not detected by LR-AS due to low read depth. For both technologies manual review of the RE alignment enhances diagnostic outcomes. Orthogonal testing for SCA27B revealed a 15% and 0% false positive rate for SR-GS and LR-AS, respectively. In conclusion, both technologies are powerful screening tools for CA. SR-GS is a mature technology currently used by diagnostic providers, requiring only minor changes in bioinformatic workflows to enable CA diagnostics. LR-AS offers considerable advantages in the context of RE detection and characterization but requires optimization before clinical implementation.

Abstract ObjectiveDespite evidence that cross-modal effects after hearing loss and cochlear implantation are primarily conveyed through synaptic gain and efficacy rather than reorganized fiber tracts, few studies have assessed cross-modal functional connectivity (CMFC) to evaluate plasticity. This study, inspired by the psychophysiological interactions (PPI) method, addresses its limitations and provides a robust approach to evaluating task-induced CMFC.DesignTwenty-two post-lingually deafened, newly implanted adult cochlear implant (CI) recipients with severe hearing loss in the contralateral ear and 17 normal-hearing (NH) subjects participated. The experiment included audio-only and visual-only speech tasks, with resting-state FC as a baseline. Functional near-infrared spectroscopy (fNIRS) measured brain imaging data one month and one year post-implantation. CI users’ speech understanding performance was evaluated one year after implantation.ResultsA negative correlation was found between average contralateral task-induced CMFC and speech outcomes, particularly in links from the angular gyrus (AG), both one month and one year post-activation. Plastic changes showed higher task-induced CMFC in AG compared to the superior temporal gyrus (STG), aligning with neural efficiency principles. Task-induced CMFC remained elevated in CI users compared to NH cohorts even after one year.ConclusionTask-induced CMFC can serve as a significant marker of cross-modal plasticity and speech performance in CI recipients, indicating increased reliance on cross-modal processing in one year after implantation.

Abstract Invasive neural electrodes prepared from materials with miniaturized geometrical size could improve the longevity of implants by reducing the chronic inflammatory response. Graphene-based microfibers with tunable porous structures have a large electrochemical surface area (ESA)/geometrical surface area (GSA) ratio that has been reported to possess low impedance and high charge injection capacity (CIC), yet the control of the porous structure remains to be fully investigated. In this study, we introduce wet-spun graphene-based electrodes with pores tuned by sucrose concentrations in the coagulation bath. The electrochemical properties of thermally reduced rGO were optimized by adjusting the ratio of rGO to sucrose, resulting in significantly lower impedance, higher CIC, and higher charge storage capacity (CSC) than platinum microwires. Tensile and insertion tests confirmed that optimized electrodes had sufficient strength to ensure a 100% insertion success rate with low angle shift, thus allowing precise implantation without the need for additional mechanical enhancement. Acutein-vivorecordings from the auditory cortex found low impedance benefits from the recorded amplitude of spikes, leading to an increase in the signal-to-noise ratio (SNR).Ex-vivorecordings from hippocampal brain slices demonstrate that it is possible to record and/or stimulate with graphene-based electrodes with good fidelity compared with conventional electrodes.