Changes In Behavioral Thresholds Research Articles

Digital Live Imaging of Intraoperative Electrocochleography - First Description of Feasibility and Hearing Preservation During Cochlear Implantation.

Intraoperative electrocochleography (ECochG) during cochlear implantation is a promising tool to preserve residual hearing. However, the time gap between insertion of the electrode and acoustic feedback from the audiologist to the surgeon can cause delay and subsequently irreparable damage to cochlear structures. In this feasibility study, for the first time, real-time visualization of intraoperative ECochG via digital microscope display directly to the surgeon was successfully performed in four patients. Four patients with residual hearing underwent cochlear implantation. Intraoperative electrocochleography responses were collected and direct visualization during the time of electrode insertion into the surgeon's field of view in the binoculars using augmented real-time digital imaging was realized. The time of electrode insertion was recorded. Hearing preservation was determined by testing postoperative changes in behavioral thresholds. Digital live visualization of intraoperative ECochG using image augmentation in a digital microscope was successfully performed in all cases and enabled direct adaptation of the surgeon's insertion behavior. Mean time of electrode insertion was 129.8 seconds. Postoperative behavioral thresholds were comparable to preoperative taken thresholds. Preservation of residual hearing in the low frequency range was possible. This study is the first to describe digital visualization of intraoperative electrocochleography as a new method enabling the surgeon to directly react to changes in amplitude of the cochlea microphonics. Our results show that augmentation of the intraoperative live imaging with electrical potentials could add to hearing preservation during cochlear implantation.

Psychoacoustic and electrophysiological electric-acoustic interaction effects in cochlear implant users with ipsilateral residual hearing

Cochlear implant users with ipsilateral residual hearing combine acoustic and electric hearing in one ear, this is called electric-acoustic stimulation (EAS). In EAS users, masking can be shown for electric probes in the presence of acoustic maskers and vice versa. Masking effects in acoustic hearing are generally attributed to nonlinearities of the basilar membrane and hair cell adaptation effects. However, similar masking patterns are observed more centrally in electric hearing. Consequently, there is no consensus so far on the level of interaction between the two modalities. Animal studies have shown that electric-acoustic interaction effects can result in reduced physiological responses in the cochlear nerve and the inferior colliculus. In CI users with residual hearing, it has recently become feasible to record intracochlear potentials with a high spatial resolution via the implanted electrode array. An investigation of the electrophysiological effects during combined electric-acoustic stimulation in humans might be used to assess peripheral mechanisms of masking.Seventeen MED-EL Flex electrode users with ipsilateral residual hearing participated in both a behavioral and a physiological electric-acoustic masking experiment. Psychoacoustic methods were used to measure the changes in behavioral thresholds due to the presence of a masker of the opposing modality. Subjects were stimulated electrically with unmodulated pulse trains using a research interface and acoustically with pure tones delivered via headphones. Auditory response telemetry was used to obtain objective electrophysiological changes of electrically evoked compound action potential and electrocochleography for electric, acoustic and combined electric-acoustic presentation in the same subjects.Behavioral thresholds of probe tones, either electric or acoustic, were significantly elevated in the presence of acoustic or electric maskers, respectively. 15 subjects showed significant electric threshold elevation with acoustic masking that did not depend on the electric-acoustic frequency difference (EAFD), a measure for the proximity of stimulation sites in the cochlea. Electric masking showed significant threshold elevation in eleven subjects, which depended significantly on EAFD. In the electrophysiological masking experiment, reduced responses to electric and acoustic stimulation with additional stimulation of the opposing modality were observed. Results showed a similar asymmetry as the psychoacoustic masking experiment. Response reduction was smaller than threshold elevation, especially for electric masking. Some subjects showed reduced responses to acoustic stimulation with electric masking, especially for small EAFD. The reduction of electrically evoked responses was significant in some subjects. No correlation was observed between psychoacoustic and electrophysiological masking results.From present study, it can be concluded that both electric and acoustic stimulation mask each other when presented simultaneously. Electrophysiological measurements indicate that masking effects are already to some extent present in the periphery.

Delayed changes in auditory status in cochlear implant users with preserved acoustic hearing

This retrospective review explores delayed-onset hearing loss in 85 individuals receiving cochlear implants designed to preserve acoustic hearing at the University of Iowa Hospitals and Clinics between 2001 and 2015. Repeated measures of unaided behavioral audiometric thresholds, electrode impedance, and electrically evoked compound action potential (ECAP) amplitude growth functions were used to characterize longitudinal changes in auditory status. Participants were grouped into two primary categories according to changes in unaided behavioral thresholds: (1) stable hearing or symmetrical hearing loss and (2) delayed loss of hearing in the implanted ear. Thirty-eight percent of this sample presented with delayed-onset hearing loss of various degrees and rates of change. Neither array type nor insertion approach (round window or cochleostomy) had a significant effect on prevalence. Electrode impedance increased abruptly for many individuals exhibiting precipitous hearing loss; the increase was often transient. The impedance increases were significantly larger than the impedance changes observed for individuals with stable or symmetrical hearing loss. Moreover, the impedance changes were associated with changes in behavioral thresholds for individuals with a precipitous drop in behavioral thresholds. These findings suggest a change in the electrode environment coincident with the change in auditory status. Changes in ECAP thresholds, growth function slopes, and suprathreshold amplitudes were not correlated with changes in behavioral thresholds, suggesting that neural responsiveness in the region excited by the implant is relatively stable. Further exploration into etiology of delayed-onset hearing loss post implantation is needed, with particular interest in mechanisms associated with changes in the intracochlear environment.

Round window electrocochleography before and after cochlear implant electrode insertion.

Previous reports have documented the feasibility of utilizing electrocochleographic (ECoG) responses to acoustic signals to assess trauma caused during cochlear implantation. The hypothesis is that intraoperative round window ECoG before and after electrode insertion will help predict postoperative hearing preservation outcomes in cochlear implant recipients. Prospective cohort study. Intraoperative round window ECoG responses were collected from 31 cochlear implant recipients (14 children and 17 adults) immediately prior to and just after electrode insertion. Hearing preservation was determined by postoperative changes in behavioral thresholds. On average, the postinsertion response was smaller than the preinsertion response by an average of 4 dB across frequencies. However, in some cases (12 of 31) the response increased after insertion. The subsequent hearing loss was greater than the acute loss in the ECoG, averaging 22 dB across the same frequency range (250-1,000 Hz). There was no correlation between the change in the ECoG response and the corresponding change in audiometric threshold. Intraoperative ECoG is a sensitive method for detecting electrophysiologic changes during implantation but had limited prognostic value regarding hearing preservation in the current conventional cochlear implant patient population where hearing preservation was not intended. 2b Laryngoscope, 126:1193-1200, 2016.

Auditory event-related dynamics of the EEG spectrum and effects of exposure to tones

A new measure of event-related brain dynamics, the event-related spectral perturbation (ERSP), is introduced to study event-related dynamics of the EEG spectrum induced by, but not phase-locked to, the onset of the auditory stimuli. The ERSP reveals aspects of event-related brain dynamics not contained in the ERP average of the same response epochs. Twenty-eight subjects participated in daily auditory evoked response experiments during a 4 day study of the effects of 24 h free-field exposure to intermittent trains of 89 dB low frequency tones. During evoked response testing, the same tones were presented through headphones in random order at 5 sec intervals. No significant changes in behavioral thresholds occurred during or after free-field exposure. ERSPs induced by target pips presented in some inter-tone intervals were larger than, but shared common features with, ERSPs induced by the tones, most prominently a ridge of augmented EEG amplitude from 11 to 18 Hz, peaking 1–1.5 sec after stimulus onset. Following 3–11 h of free-field exposure, this feature was significantly smaller in tone-induced ERSPs; target-induced ERSPs were not similarly affected. These results, therefore, document systematic effects of exposure to intermittent tones on EEG brain dynamics even in the absence of changes in auditory thresholds.

Acoustic-reflex activity and behavioral thresholds following exposure to noise.

The relationships between properties of the acoustic reflex and temporary threshold shift (TTS) were examined in eight subjects exposed to a 95 dB SPL, 1.0-kHz octave-band noise for 4 h. The specific pattern of TTS obtained from this exposure was consistent with the expected sensitivity changes along the cochlear partition. Maximum decrease in behavioral thresholds was noted at 1.4 kHz with significant TTS also occurring at 2.0 and 4.0 kHz. Behavioral threshold at 0.5 kHz, one octave below the center frequency of exposure, was not affected. Significant reflex threshold shift (RTS) occurred at 1.4 and 2.0 kHz. In addition, RTS was noted at 0.5 kHz in the absence of any change in behavioral sensitivity at that frequency. Magnitude of the acoustic reflex was examined from threshold to 10-dB sensation level. A systematic reduction in magnitude was noted during the noise exposure for 1.4 and 2.0 kHz. The same pattern did not emerge for 0.5 kHz. Magnitude of the acoustic reflex pre-exposure was significantly correlated to TTS at 1.4 kHz. Changes in acoustic reflex thresholds and magnitudes followed the same time course as changes in behavioral thresholds during the growth and recovery periods.