English MODULATION OF MELATONIN SECRETION WITH TRANSCUTANEOUS AURICULAR NERVE STIMULATION: A CASE STUDY

The main study objective was to test the hypothesis that selective electrical transcutaneous auricular nerve stimulation (tANS) under forenoon daylight conditions induces melatonin secretion in a 64-year-old male patient with angina pectoris, hypercholesterolomy and coronary artery disease, assuming that it has beneficial effects on accompanied insomnia (Regensburg Insomnia Scale (RIS) = 22 points, the total score ranges from 0 to 40). Silicone stimulation plugs, with two platinum stimulating cathodes each, were inserted into the left and right external ears. Afterwards, one-second-long pulse trains of cathodic, biphasic and current regulated stimulating pulses at stimulating charge density Cd of 50.88 µC/cm2 and frequency of 25 Hz, were delivered for 30 min to selected sites at the upper and lower part of the left and right Cymba Conchae (CC), respectively. The common anode was attached to the neck. The time gap between the pulse trains was measured by the patient using a tactile sensor and was about 250 ms. The results showed that selective tANS under forenoon daylight conditions increased melatonin saliva levels in all the trials accomplished in a patient. Precisely, the lowest increase was obtained in trials with lower right (LR) CC, while the highest increase was obtained in upper-right (UR) CC trials.

Partial spectral and temporal coherence of plane-wave pulse trains in second-harmonic generation

We study the spectral and temporal coherence effects in the passage of a Gaussian Schell-model (GSM) scalar, plane-wave pulse train through a slab of nonlinear optical crystal exhibiting second-harmonic generation. We show that due to the nonlinear interaction the temporal and spectral degrees of coherence of the fundamental (F) and second-harmonic (SH) pulse trains at the exit facet may deviate markedly from the GSM and the global degree of coherence of the SH wave generally decreases with increasing incident F beam intensity. In addition, we find that due to the partial coherence of the incident GSM field the transmitted SH wave may show a double-peaked intensity distribution.

Rate discrimination training may partially restore temporal processing abilities from age-related deficits

The ability to understand speech in complex environments depends on the ability of the brain to preserve the precise timing characteristics of the speech signal. Age-related declines in temporal processing may contribute to the communication difficulties in challenging listening conditions experienced by older adults. The study purpose was to evaluate the effects of rate discrimination training on auditory temporal processing. A double-blind, randomized control design assigned 77 young normal-hearing, older normal-hearing, and older hearing-impaired listeners to one of two treatment groups: experimental (rate discrimination for 100-Hz and 300-Hz pulse trains) and active control (tone detection in noise). All listeners were evaluated during pre- and post-training sessions using perceptual rate discrimination of 100-, 200-, 300-, and 400-Hz band-limited pulse trains and auditory steady-state responses (ASSRs) to the same stimuli. Training generalization was evaluated using several temporal processing measures and sentence recognition tests that included time-compressed and reverberant speech stimuli. Results demonstrated a session x training group interaction for perceptual and ASSR testing to the trained frequencies (100 and 300 Hz), driven by greater improvements in the training group than in the active control group. Further, post-test rate discrimination of the older listeners reached levels that were equivalent to those of the younger listeners at pre-test. The training-specific gains generalized to untrained frequencies (200 and 400 Hz), but not to other temporal processing or sentence recognition measures. Further, non-auditory inhibition/attention performance predicted training-related improvement in rate discrimination. Overall, the results demonstrate the potential for auditory training to partially restore temporal processing in older listeners and highlight the role of cognitive function in these gains.

Reweighting of Binaural Localization Cues in Bilateral Cochlear-Implant Listeners

Normal-hearing (NH) listeners rely on two binaural cues, the interaural time (ITD) and level difference (ILD), for azimuthal sound localization. Cochlear-implant (CI) listeners, however, rely almost entirely on ILDs. One reason is that present-day clinical CI stimulation strategies do not convey salient ITD cues. But even when presenting ITDs under optimal conditions using a research interface, ITD sensitivity is lower in CI compared to NH listeners. Since it has recently been shown that NH listeners change their ITD/ILD weighting when only one of the cues is consistent with visual information, such reweighting might add to CI listeners’ low perceptual contribution of ITDs, given their daily exposure to reliable ILDs but unreliable ITDs. Six bilateral CI listeners completed a multi-day lateralization training visually reinforcing ITDs, flanked by a pre- and post-measurement of ITD/ILD weights without visual reinforcement. Using direct electric stimulation, we presented 100- and 300-pps pulse trains at a single interaurally place-matched electrode pair, conveying ITDs and ILDs in various spatially consistent and inconsistent combinations. The listeners’ task was to lateralize the stimuli in a virtual environment. Additionally, ITD and ILD thresholds were measured before and after training. For 100-pps stimuli, the lateralization training increased the contribution of ITDs slightly, but significantly. Thresholds were neither affected by the training nor correlated with weights. For 300-pps stimuli, ITD weights were lower and ITD thresholds larger, but there was no effect of training. On average across test sessions, adding azimuth-dependent ITDs to stimuli containing ILDs increased the extent of lateralization for both 100- and 300-pps stimuli. The results suggest that low-rate ITD cues, robustly encoded with future CI systems, may be better exploitable for sound localization after increasing their perceptual weight via training.

Virtual reality validation of naturalistic modulation strategies to counteract fading in retinal stimulation

Objective: Temporal resolution is a key challenge in artificial vision. Several prosthetic approaches are limited by the perceptual fading of evoked phosphenes upon repeated stimulation from the same electrode. Therefore, implanted patients are forced to perform active scanning, via head movements, to refresh the visual field viewed by the camera. However, active scanning is a draining task, and it is crucial to find compensatory strategies to reduce it. Approach: To address this question, we implemented perceptual fading in simulated prosthetic vision using virtual reality. Then, we quantified the effect of fading on two indicators: the time to complete a reading task and the head rotation during the task. We also tested if stimulation strategies previously proposed to increase the persistence of responses in retinal ganglion cells to electrical stimulation could improve these indicators. Main results: This study shows that stimulation strategies based on interrupted pulse trains and randomisation of the pulse duration allows significant reduction of both the time to complete the task and the head rotation during the task. Significance: The stimulation strategy used in retinal implants is crucial to counteract perceptual fading and to reduce active head scanning during prosthetic vision. In turn, less active scanning might improve the patient's comfort in artificial vision.

Generation of Subpicosecond Pulse Trains in Fiber Cascades Comprising a Cylindrical Waveguide with Propagating Refractive Index Wave

A cylindrical waveguide structure with the running refractive index wave has been recently demonstrated as a means for the generation of high-repetition-rate pulse trains. The operation mechanism involves a proper combination of the frequency modulation and modulation instability simultaneously experienced by the input continuous wave (CW) signal as it propagates through the cylinder waveguide. Here, we explore the same idea but employ the cylindrical waveguide only as a part of the cascaded optical fiber configuration now comprising both passive and active optical fiber segments. The new system design enables the improved control of the pulse train formation process in the cascaded system elements, relaxes strong requirements for the CW signal power, and provides an additional optical gain for the advanced pulse peak power scaling. In particular, using a low-amplitude, weakly modulated, continuous wave as an input signal we explore and optimize the nonlinear mechanisms underlying its cascaded transformation into the train of kilowatt peak power picosecond pulses.

High-Peak Power Frequency Modulation Pulse Generation in Cascaded Fiber Configurations with Inscribed Fiber Bragg Grating Arrays

We explored the dynamics of frequency-modulated (FM) pulses in a cascaded fiber configuration comprising one active and one passive optical fiber with multiple fiber Bragg gratings (FBGs) of different periods inscribed over the fiber configuration length. We present a theoretical formalism to describe the mechanisms of the FM pulse amplification and pulse compression in such fiber cascades resulting in peak powers up to ~0.7 MW. In combination with the decreasing dispersion fibers, the considered cascade configuration enables pico- and sub-picosecond pulse trains with a sub-terahertz repetition rate and sub-kW peak power generated directly from the continuous optical signal.