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Optogenetics comprise a promising alternative to electrical stimulation for characterization of neural circuits and for the next generation of neural prostheses. Optogenetic stimulation relies on expression of photosensitive microbial proteins in animal cells to initiate a flow of ions into the cells in response to visible light. Here, we generated a novel transgenic mouse model in which we studied the optogenetic activation of spiral ganglion neurons, the primary afferent neurons of the auditory system, and showed a strong optogenetic response, with a similar amplitude as the acoustically evoked response. A twofold increase in the level of channelrhodopsin expression significantly increased the photosensitivity at both the single cell and organismal levels but also partially compromised the native electrophysiological properties of the neurons. The importance of channelrhodopsin expression level to optogenetic stimulation, revealed by these quantitative measurements, will be significant for the characterization of neural circuitry and for the use of optogenetics in neural prostheses. NEW & NOTEWORTHY This study reveals a dose-response relationship between channelrhodopsin expression and optogenetic excitation. Both single cell and organismal responses depend on the expression level of the heterologous protein. Expression level of the opsin is thus an important variable in determining the outcome of an optogenetic experiment. These results are key to the implementation of neural prostheses based on optogenetics, such as next generation cochlear implants, which would use light to elicit a neural response to sound. [ABSTRACT FROM AUTHOR]

Objective Few studies have examined operative times for cochlear implantation (CI) using multivariable linear regression analyses to identify predictors of case length. Herein, we assess whether trainee participation, among other factors, influences operating room (OR) times. Methods We retrospectively reviewed total OR and procedural times for isolated unilateral implants over a 5-year period (2009–2013) in children and adults. Total operating and procedural times were compared. Multivariable linear regression analyses were used to identify predictors of procedural time. Results We identified a total of 455 unilateral CI procedures (n = 35 pediatric, n = 420 adult). Mean total OR time was 193.6 minutes (SD = 58.9 minutes) and mean procedural time was 147.1 minutes (SD = 56.2). The presence of trainees was associated with a significant difference in procedure time: 149.9 minutes (SD = 54.9) with trainees versus 136.6 minutes (SD = 59.9) without trainees, P = 0.0375. Trainee involvement did not significantly increase total OR time: 196.3 minutes (SD = 56.9) with trainees versus 183.8 minutes (SD = 65.0) without trainees, P = 0.0653. Surgeon identity was also associated with differences in procedural time (P < 0.001). Patient age, gender, American Society of Anesthesiologists classification, and pediatric designation had no significant impact on length of case. Conclusions Major predictors of longer procedural OR times for CI are surgeon identity and trainee participation. Few published data exist on length of CI in an academic setting using multivariable linear regression analyses. Our data may be instructive for comparative analyses and have implications for operative planning and surgical education. [ABSTRACT FROM AUTHOR]

The mouse auditory cortex (ACtx) contains two core fields-primary auditory cortex (A1) and anterior auditory field (AAF)-arranged in a mirror reversal tonotopic gradient. The best frequency (BF) organization and naming scheme for additional higher order fields remain a matter of debate, as does the correspondence between smoothly varying global tonotopy and heterogeneity in local cellular tuning. Here, we performed chronic widefield and two-photon calcium imaging from the ACtx of awake Thy1-GCaMP6s reporter mice. Data-driven parcellation of widefield maps identified five fields, including a previously unidentified area at the ventral posterior extreme of the ACtx (VPAF) and a tonotopically organized suprarhinal auditory field (SRAF) that extended laterally as far as ectorhinal cortex. Widefield maps were stable over time, where single pixel BFs fluctuated by less than 0.5 octaves throughout a 1-month imaging period. After accounting for neuropil signal and frequency tuning strength, BF organization in neighboring layer 2/3 neurons was intermediate to the heterogeneous salt and pepper organization and the highly precise local organization that have each been described in prior studies. Multiscale imaging data suggest there is no ultrasonic field or secondary auditory cortex in the mouse. Instead, VPAF and a dorsal posterior (DP) field emerged as the strongest candidates for higher order auditory areas., (© The Author(s) 2019. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The auditory brainstem implant (ABI) restores hearing in patients with damaged auditory nerves. One of the main ideas to improve the efficacy of ABIs is to increase spatial specificity of stimulation, in order to minimize extra-auditory side-effects and to maximize the tonotopy of stimulation. This study reports on the development of a microfabricated conformable electrode array with small (100 μ m diameter) electrode sites. The latter are coated with a conducting polymer, PEDOT:PSS, to offer high charge injection properties and to safely stimulate the auditory system with small stimulation sites. We report on the design and fabrication of the polymer implant, and characterize the coatings in physiological conditions in vitro and under mechanical deformation. We characterize the coating electrochemically and during bending tests. We present a proof of principle experiment where the auditory system is efficiently activated by the flexible polymeric interface in a rat model. These results demonstrate the potential of using conducting polymer coatings on small electrode sites for electrochemically safe and efficient stimulation of the central auditory system.