tACS-mediated modulation of the auditory steady-state response as seen with MEG.

BACKGROUND: Previous studies have shown that transcranial electrical stimulation can be successfully applied during simultaneous MEG measurements. In particular, using beamforming they have established that changes of stimulus induced as well as evoked activity can be inspected during transcranial alternating current stimulation (tACS). OBJECTIVE/HYPOTHESIS: We studied tACS-mediated changes of the auditory steady-state response (ASSR), hypothesizing that-due to the putatively inhibitory role of alpha oscillations-these evoked responses would be diminished. METHODS: We compared ASSRs in conditions with and without 12-Hz and 6.5-Hz sinusoidal 1.5 mA tACS, applied bilaterally over temporal areas. Source-level activity was estimated using a linearly constrained minimum variance beamformer and compared across tACS conditions using paired t-tests following a condition-internal normalization procedure. CONCLUSIONS: By separating the electrical and auditory stimulation to non-overlapping parts of the frequency spectrum, we were able to compare auditory-evoked steady-state activity across tACS conditions. We observed a significant decrease in normalized ASSR power in the 12-Hz tACS condition, illustrating that tACS could induce immediate changes in auditory evoked activity. This study sets a methodology to further interrogate the causal roles of oscillatory dynamics in auditory cortices, as well as suggests perspectives for employing tACS in clinical contexts.

Balloon Eustachian tuboplasty under local anesthesia: Is it feasible?

OBJECTIVE: To study whether balloon Eustachian tuboplasty (BET) is a feasible and safe procedure under local anesthesia. STUDY DESIGN: Prospective multicenter case-control study. METHODS: Patients undergoing either BET (n = 13) or endoscopic sinus surgery (ESS) (n = 12) under local anesthesia, with the possibility of sedation and analgesia, were monitored during the procedure and recovery period for possible adverse effects. After the procedure, the patients responded to a questionnaire assessing their experience. RESULTS: No adverse effects were detected in the BET group. Patients in the BET group reported similar Visual Analog Scale scores for pain during the operation as the ESS group (5.0 ± 0.7 vs. 3.2 ± 0.7, mean ± standard error of the mean). However, patients in the BET group experienced more discomfort (4.2 ± 0.6 vs. 2.5 ± 0.3, respectively, P = 0.049). Seventy-seven and 92% of the patients in the BET and ESS groups, respectively, considered the anesthesia and pain relief to be sufficient. Patients from both the BET and ESS groups were almost devoid of pain 1 to 2 hours postoperatively (0.8 ± 0.2 and 1.4 ± 0.3, respectively). In total, 12 of 13 patients in the BET group, and all 12 patients in the ESS group, would choose local anesthesia with sedation and analgesia if they needed to undergo the same procedure again. CONCLUSION: BET is a safe and feasible procedure under monitored anesthesia care, including local anesthesia along with sedation and analgesia. There is need for further methodological improvement to reduce pain and discomfort during the operation. LEVEL OF EVIDENCE: 4. Laryngoscope, 127:1021-1025, 2017.

Auditory localization by subjects with unilateral tinnitus.

Tinnitus is associated with changes in neural activity. How such alterations impact the localization ability of subjects with tinnitus remains largely unexplored. In this study, subjects with self-reported unilateral tinnitus were compared to subjects with matching hearing loss at high frequencies and to normal-hearing subjects in horizontal and vertical plane localization tasks. Subjects were asked to localize a pink noise source either alone or over background noise. Results showed some degree of difference between subjects with tinnitus and subjects with normal hearing in horizontal plane localization, which was exacerbated by background noise. However, this difference could be explained by different hearing sensitivities between groups. In vertical plane localization there was no difference between groups in the binaural listening condition, but in monaural listening the tinnitus group localized significantly worse with the tinnitus ear. This effect remained when accounting for differences in hearing sensitivity. It is concluded that tinnitus may degrade auditory localization ability, but this effect is for the most part due to the associated levels of hearing loss. More detailed studies are needed to fully disentangle the effects of hearing loss and tinnitus.

Characteristics and international comparability of the Finnish matrix sentence test in cochlear implant recipients.

OBJECTIVES: The first Finnish sentence-based speech test in noise--the Finnish matrix sentence test--was recently developed. The aim of this study was to determine the characteristics of the new test with respect to test-retest reliability, speech recognition curve, and international comparability in Finnish cochlear implant (CI) recipients. DESIGN: The speech reception thresholds (SRT) were measured by means of an adaptive test procedure and compared with the results of the traditional Finnish word test. Additional measurements for concurrent slope and SRT estimation were conducted to determine the speech recognition curve and to check the test-retest reliability. STUDY SAMPLE: The measurements were performed on 78 Finnish CI recipients. In a subset of 25 patients, additional measurements for test-retest reliability and slope determination were performed. RESULTS: The mean SRT was -3.5 ± 1.7 dB SNR, with only a weak correlation with the Finnish word test. Test-retest reliability was within ± 1 dB and the mean slope of the speech recognition curve was 14.6 ± 3.6 %/dB. The rehabilitation results were similar to the results published for the German matrix test. CONCLUSIONS: The Finnish matrix test was found to be suitable and efficient in CI recipients with similar characteristics as the German matrix test.

Transcutaneous vagus nerve stimulation modulates tinnitus-related beta- and gamma-band activity.

OBJECTIVES: The ability of a treatment method to interfere with tinnitus-related neural activity patterns, such as cortical gamma rhythms, has been suggested to indicate its potential in relieving tinnitus. Therapeutic modulation of gamma-band oscillations with vagus nerve stimulation has been recently reported in epileptic patients. The aim of this study was to investigate the effects of transcutaneous vagus nerve stimulation (tVNS) on neural oscillatory patterns. DESIGN: We calculated the power spectral density and synchrony of magnetoencephalography recordings during auditory stimulation in seven tinnitus patients and eight normal-hearing control subjects. Comparisons between subject groups were performed to reveal electrophysiological markers of tinnitus. tVNS-specific effects within each group were studied by comparing recording blocks with and without tVNS. We also investigated the correlation of each measure with individual ratings of tinnitus distress, as measured by the tinnitus handicap inventory questionnaire. RESULTS: Tinnitus patients differed from controls in the baseline condition (no tVNS applied), measured by both cortical oscillatory power and synchronization, particularly at beta and gamma frequencies. Importantly, we found tVNS-induced changes in synchrony, correlating strongly with tinnitus handicap inventory scores, at whole-head beta-band (r = -0.857, p = 0.007), whole-head gamma-band (r = -0.952, p = 0.0003), and frontal gamma-band (r = -0.952, p = 0.0003). CONCLUSIONS: We conclude that tVNS was successful in modulating tinnitus-related beta- and gamma-band activity and thus could have potential as a treatment method for tinnitus.

Motion of the tympanic membrane after cartilage tympanoplasty determined by stroboscopic holography.

Stroboscopic holography was used to quantify dynamic deformations of the tympanic membrane (TM) of the entire surface of the TM before and after cartilage tympanoplasty of the posterior or posterior-superior part of the TM. Cartilage is widely used in tympanoplasties to provide mechanical stability for the TM. Three human cadaveric temporal bones were used. A 6 mm x 3 mm oval cartilage graft was placed through the widely opened facial recess onto the medial surface of the posterior or posterior-superior part of the TM. The graft was either in contact with the bony tympanic rim and manubrium or not. Graft thickness was either 0.5 or 1.0mm. Stroboscopic holography produced displacement amplitude and phase maps of the TM surface in response to stimulus sound. Sound stimuli were 0.5, 1, 4 and 7 (or 8)kHz tones. Middle-ear impedance was measured from the motion of the entire TM. Cartilage placement generally produced reductions in the motion of the TM apposed to the cartilage, especially at 4 kHz and 7 or 8 kHz. Some parts of the TM showed altered motion compared to the control in all three cases. In general, middle-ear impedance was either unchanged or increased somewhat after cartilage reconstruction both at low (0.5 and 1 kHz) and high (4 and 7 kHz) frequencies. At 4 kHz, with the 1.0mm thick graft that was in contact with the bony tympanic rim, the impedance slightly decreased. While our earlier work with time-averaged holography allowed us to observe differences in the pattern of TM motion caused by application of cartilage to the TM, stroboscopic holography is more sensitive to TM motions and allowed us to quantify the magnitude and phase of motion of each point on the TM surface. Nonetheless, our results are similar to those of our earlier work: The placement of cartilage on the medial surface of TM reduces the motion of the TM that apposes the cartilage. These obvious local changes occur even though the cartilage had little effect on the sound-induced motion of the stapes.

Motion of the surface of the human tympanic membrane measured with stroboscopic holography.

Sound-induced motion of the surface of the human tympanic membrane (TM) was studied by stroboscopic holographic interferometery, which measures the amplitude and phase of the displacement at each of about 40,000 points on the surface of the TM. Measurements were made with tonal stimuli of 0.5, 1, 4 and 8 kHz. The magnitude and phase of the sinusoidal displacement of the TM at each driven frequency were derived from the fundamental Fourier component of the raw displacement data computed from stroboscopic holograms of the TM recorded at eight stimulus phases. The correlation between the Fourier estimates and measured motion data was generally above 0.9 over the entire TM surface. We used three data presentations: (i) plots of the phasic displacements along a single chord across the surface of the TM, (ii) phasic surface maps of the displacement of the entire TM surface, and (iii) plots of the Fourier derived amplitude and phase-angle of the surface displacement along four diameter lines that define and bisect each of the four quadrants of the TM. These displays led to some common conclusions: at 0.5 and 1kHz, the entire TM moved roughly in-phase with some small phase delay apparent between local areas of maximal displacement in the posterior half of the TM. At 4 and 8 kHz, the motion of the TM became more complicated with multiple local displacement maxima arranged in rings around the manubrium. The displacements at most of these maxima were roughly in-phase, while some moved out-of-phase. Superposed on this in- and out-of-phase behavior were significant cyclic variations in-phase with location of less than 0.2 cycles or occasionally rapid half-cycle step-like changes in-phase. The high frequency displacement amplitude and phase maps discovered in this study can not be explained by any single wave motion, but are consistent with a combination of low and higher order modal motions plus some small traveling-wave-like components. The observations of the dynamics of TM surface motion from this study will help us better understand the sound-receiving function of the TM and how it couples sound to the ossicular chain and inner ear.

Middle ear mechanics of cartilage tympanoplasty evaluated by laser holography and vibrometry.

GOALS: To assess the effects of thickness and position of cartilage used to reconstruct the tympanic membrane (TM) using a novel technique, time-averaged laser holography. BACKGROUND: Cartilage is commonly used in TM reconstruction to prevent formation of retraction pockets. The thickness, position, and shape of the cartilage graft may adversely affect TM motion and hearing. We sought to systematically investigate these parameters in an experimental setting. METHODS: Computer-assisted optoelectronic laser holography was used in 4 human cadaveric temporal bones to study sound-induced TM motion for 500 Hz to 8 kHz. Stapes velocity was measured with a laser Doppler vibrometer. Baseline (control) measurements were made with the TM intact. Measurements were repeated after a 0.5- or 1.0-mm-thick oval piece of conchal cartilage was placed on the medial TM surface in the posterior-superior quadrant. The cartilage was rotated so that it was either in contact with the bony tympanic rim and manubrium or not. RESULTS: At frequencies less than 4 kHz, the cartilage graft had only minor effects on the overall TM fringe patterns. The different conditions had no effects on stapes velocity. Greater than 4 kHz, TM motion was reduced over the grafted TM, both with 0.5- and 1.0-mm-thick grafts. No significant differences in stapes velocity were seen with the 2 different thicknesses of cartilage compared with control. CONCLUSION: Computer-assisted optoelectronic laser holography is a promising technique to investigate middle ear mechanics after tympanoplasty. Such positioning may prevent postoperative TM retraction. These findings and conclusions apply to cartilage placed in the posterior-superior TM quadrant.