The Panoramic ECAP Method: Estimating Patient-Specific Patterns of Current Spread and Neural Health in Cochlear Implant Users

AbstractThe knowledge of patient-specific neural excitation patterns from cochlear implants (CIs) can provide important information for optimizing efficacy and improving speech perception outcomes. The Panoramic ECAP (‘PECAP’) method (Cosentino et al. 2015) uses forward-masked electrically evoked compound action-potentials (ECAPs) to estimate neural activation patterns of CI stimulation. The algorithm requires ECAPs be measured for all combinations of probe and masker electrodes, exploiting the fact that ECAP amplitudes reflect the overlapping excitatory areas of both probes and maskers. Here we present an improved version of the PECAP algorithm that imposes biologically realistic constraints on the solution, that, unlike the previous version, produces detailed estimates of neural activation patterns by modelling current spread and neural health along the intracochlear electrode array and is capable of identifying multiple regions of poor neural health. The algorithm was evaluated for reliability and accuracy in three ways: (1) computer-simulated current-spread and neural-health scenarios, (2) comparisons to psychophysical correlates of neural health and electrode-modiolus distances in human CI users, and (3) detection of simulated neural ‘dead’ regions (using forward masking) in human CI users. The PECAP algorithm reliably estimated the computer-simulated scenarios. A moderate but significant negative correlation between focused thresholds and the algorithm’s neural-health estimates was found, consistent with previous literature. It also correctly identified simulated ‘dead’ regions in all seven CI users evaluated. The revised PECAP algorithm provides an estimate of neural excitation patterns in CIs that could be used to inform and optimize CI stimulation strategies for individual patients in clinical settings.

Download Full-text

The Panoramic ECAP Method: estimating patient-specific patterns of current spread and neural health in cochlear implant users

10.31234/osf.io/xrz4f ◽

2020 ◽

Author(s):

Charlotte Garcia ◽

Tobias Goehring ◽

Stefano Cosentino ◽

Richard E Turner ◽

John M. Deeks ◽

...

Keyword(s):

Cochlear Implant ◽

Electrode Array ◽

Significant Negative Correlation ◽

Patient Specific ◽

Clinical Settings ◽

Neural Activation ◽

Activation Patterns ◽

Current Spread ◽

Compound Action Potentials ◽

In Cis

The knowledge of patient-specific neural excitation patterns from cochlear implants can provide important information for optimising efficacy and improving speech perception outcomes. The Panoramic ECAP (or ‘PECAP’) method (Cosentino, et al., 2015) uses forward-masked electrically evoked compound action potentials (ECAPs) to estimate neural activation patterns of cochlear implant (CI) stimulation. The algorithm requires ECAPs be measured for loudness-balanced stimuli from all combinations of probe and masker electrodes, and takes advantage of ECAP amplitudes being a result of the overlapping excitatory areas of both probes and maskers. Here we present an improved version of the PECAP algorithm that imposes biologically realistic constraints on the solution and produces separate estimates of current spread and neural health along the length of the electrode array. The algorithm was evaluated for reliability and accuracy in three ways: (1) computer-simulated current-spread and neural-health scenarios, (2) comparisons to psychophysical correlates of neural health and electrode-modiolus distances in human CI users, and (3) detection of simulated neural ‘dead’ regions (using forward masking) in human CI users. The PECAP algorithm reliably estimated the computer simulated scenarios. A moderate but significant negative correlation between focused thresholds and PECAP’s neural health estimates was found, consistent with previous literature. It also correctly identified simulated dead regions in seven CI users. The revised PECAP algorithm provides an estimate of the electrode-to-neuron interface in CIs that could be used to inform and optimize CI stimulation strategies for individual patients in clinical settings.

Download Full-text

SpeedCAP: An Efficient Method for Estimating Neural Activation Patterns Using Electrically-Evoked Compound Action-Potentials in Cochlear Implant Users

10.31234/osf.io/vd6kq ◽

2021 ◽

Author(s):

Charlotte Garcia ◽

John M. Deeks ◽

Tobias Goehring ◽

Daniele Borsetto ◽

Manohar Bance ◽

...

Keyword(s):

Data Collection ◽

Cochlear Implant ◽

Action Potentials ◽

Forward Masking ◽

Patient Specific ◽

Neural Activation ◽

Current Spread ◽

Wide Range ◽

Compound Action Potentials ◽

Compound Action

Objectives: Electrically-Evoked Compound Action-Potentials (ECAPs) can be recorded using the electrodes in a cochlear implant (CI) and represent the synchronous responses of the electrically-stimulated auditory-nerve. ECAPs can be obtained using a forward-masking method that measures the neural response to a probe and masker electrode separately and in combination. The Panoramic ECAP (PECAP) method measures ECAPs using multiple combinations of masker and probe electrodes and uses a nonlinear optimization algorithm to estimate current spread from each electrode and neural health along the cochlea. However, the measurement of ECAPs from multiple combinations of electrodes is too time-consuming for use in clinics. This study proposes and evaluates a fast version of the PECAP measurements, SpeedCAP, that minimises recording time by exploiting redundancies between multiple ECAP measures, and that can be applied to methods where multiple ECAPs are required. Design: In the first study, 11 users of Cochlear Limited CIs took part. ECAPs were recorded using the forward-masking artefact-cancellation technique at the most comfortable loudness level (MCL) for every combination of masker and probe electrodes for all active electrodes in the users’ MAPs, as per the standard PECAP recording paradigm. The same current levels and recording parameters were then used to collect ECAPs in the same users with the SpeedCAP method. The ECAP amplitudes were then compared between the two conditions, as were the corresponding estimates of neural health and current spread calculated using the PECAP method described by Garcia et al (2021). The second study measured SpeedCAP intra-operatively in 8 CI patients and with all maskers and probes presented at the same current level to assess feasibility. ECAPs for the subset of conditions where the masker and probe were presented on the same electrode were compared to those obtained using the slower approach leveraged by the standard clinical software. Results: Data collection time was reduced from 45 (PECAP) to 8 (SpeedCAP) minutes. There were no significant differences between normalized root mean squared error (RMSE) repeatability metrics for post-operative PECAP and SpeedCAP data, nor for the RMSEs calculated between PECAP and SpeedCAP data. When between-participant differences were removed, both the neural health (r = 0.73) and current spread (r = 0.65) estimates were significantly correlated (p < 0.0001, df = 218) between SpeedCAP and PECAP conditions across all electrodes. Valid ECAPs were obtained in all patients in the second study, demonstrating intra-operative feasibility of SpeedCAP. No significant differences in RMSEs were detectable between post- and intra-operative ECAP measurements. Conclusions: The improved efficiency of SpeedCAP provides time savings facilitating multi-electrode ECAP recordings in routine clinical practice. The SpeedCAP data collection is sufficiently quick to record intra-operatively, and adds no significant error to the ECAP amplitudes. Such measurements could thereafter be submitted to models such as PECAP to provide patient-specific patterns of neural activation to inform programming of clinical MAPs and/or identify causes of poor performance at the electrode-nerve interface of CI users. The speed and accuracy of these measurements also opens up a wide range of additional research questions to be addressed.

Download Full-text

Multistage nonlinear optimization to recover neural activation patterns from evoked compound action potentials of cochlear implant users

IEEE Transactions on Biomedical Engineering ◽

10.1109/tbme.2015.2476373 ◽

2015 ◽

pp. 1-1 ◽

Cited By ~ 4

Author(s):

Stefano Cosentino ◽

Etienne Gaudrain ◽

John Deeks ◽

Robert Carlyon

Keyword(s):

Cochlear Implant ◽

Nonlinear Optimization ◽

Action Potentials ◽

Neural Activation ◽

Activation Patterns ◽

Compound Action Potentials ◽

Compound Action

Download Full-text

Negative symptoms in schizophrenia show association with amygdala volumes and neural activation during affective processing

Acta Neuropsychiatrica ◽

10.1017/neu.2015.11 ◽

2015 ◽

Vol 27 (4) ◽

pp. 213-220 ◽

Cited By ~ 11

Author(s):

Christoffer Rahm ◽

Benny Liberg ◽

Greg Reckless ◽

Olga Ousdal ◽

Ingrid Melle ◽

...

Keyword(s):

Negative Correlation ◽

Negative Symptoms ◽

Significant Negative Correlation ◽

Group Differences ◽

Affective Processing ◽

Neural Activation ◽

Healthy Controls ◽

Activation Patterns ◽

Affective Stimuli ◽

Amygdala Volume

ObjectivesNegative symptoms in schizophrenia have been associated with structural and functional alterations of the amygdala. We hypothesised that there would be between-group differences in amygdala volume and neural activation patterns during processing of affective stimuli among patients with schizophrenia and healthy controls. We further hypothesised correlations between neuroimaging metrics and clinical ratings of negative symptoms in patients with schizophrenia.MethodsWe used structural and functional magnetic resonance imaging to assess volume and neural activation of the amygdala in 28 patients with schizophrenia and 28 healthy controls.ResultsWe found no between-group differences in amygdala volume or neural activation. However, we found a significant negative correlation between emotional blunting and neural activation in the left amygdala during processing of positive affect. We also found a significant negative correlation between stereotyped thinking and the volume of right amygdala.ConclusionOur findings implicate the amygdala in a subgroup of negative symptoms in schizophrenia that are characterised by reduced expression with blunted affect and stereotyped thinking.

Download Full-text

The Perception of Ramped Pulse Shapes in Cochlear Implant Users

Trends in Hearing ◽

10.1177/23312165211061116 ◽

2021 ◽

Vol 25 ◽

pp. 233121652110611

Author(s):

Charlotte Amalie Navntoft ◽

David M. Landsberger ◽

Tania Rinaldi Barkat ◽

Jeremy Marozeau

Keyword(s):

Single Channel ◽

Spiral Ganglion ◽

Electrode Array ◽

Neural Activation ◽

Activation Patterns ◽

Power Efficient ◽

Threshold Detection ◽

Electric Pulses ◽

Significant Difference ◽

Ganglion Neurons

The electric stimulation provided by current cochlear implants (CI) is not power efficient. One underlying problem is the poor efficiency by which information from electric pulses is transformed into auditory nerve responses. A novel stimulation paradigm using ramped pulse shapes has recently been proposed to remedy this inefficiency. The primary motivation is a better biophysical fit to spiral ganglion neurons with ramped pulses compared to the rectangular pulses used in most contemporary CIs. Here, we tested the hypotheses that ramped pulses provide more efficient stimulation compared to rectangular pulses and that a rising ramp is more efficient than a declining ramp. Rectangular, rising ramped and declining ramped pulse shapes were compared in terms of charge efficiency and discriminability, and threshold variability in seven CI listeners. The tasks included single-channel threshold detection, loudness-balancing, discrimination of pulse shapes, and threshold measurement across the electrode array. Results showed that reduced charge, but increased peak current amplitudes, was required at threshold and most comfortable levels with ramped pulses relative to rectangular pulses. Furthermore, only one subject could reliably discriminate between equally-loud ramped and rectangular pulses, suggesting variations in neural activation patterns between pulse shapes in that participant. No significant difference was found between rising and declining ramped pulses across all tests. In summary, the present findings show some benefits of charge efficiency with ramped pulses relative to rectangular pulses, that the direction of a ramped slope is of less importance, and that most participants could not perceive a difference between pulse shapes.

Download Full-text