Location Of Recording Electrode Research Articles

Evaluation of Real-Time Intracochlear Electrocochleography for Guiding Cochlear Implant Electrode Array Position.

This study evaluates intracochlear electrocochleography (ECochG) for real-time monitoring during cochlear implantation. One aim tested whether adjusting the recording electrode site would help differentiate between atraumatic and traumatic ECochG amplitude decrements. A second aim assessed whether associations between ECochG amplitude decrements and post-operative hearing loss were weaker when considering hearing sensitivity at the ECochG stimulus frequency compared to a broader frequency range. Eleven adult cochlear implant recipients who were candidates for electro-acoustic stimulation participated. Single-frequency (500-Hz) ECochG was performed during cochlear implantation; the amplitude of the first harmonic of the difference waveform was considered. Post-operative hearing preservation at 500 Hz ranged from 0 to 94%. The expected relationship between ECochG amplitude decrements and hearing preservation was observed, though the trend was not statistically significant, and predictions were grossly inaccurate for two participants. Associations did not improve when considering alternative recording sites or hearing sensitivity two octaves above the ECochG stimulus frequency. Intracochlear location of a moving recording electrode is a known confound to real-time interpretation of ECochG amplitude fluctuations, which was illustrated by the strength of the correlation with ECochG amplitude decrements. Multiple factors contribute to ECochG amplitude patterns and to hearing preservation; these results highlight the confounding influence of intracochlear recording electrode location on the ECochG.

Effects of jawphone position and stimulus frequency on the auditory brainstem response in bottlenose dolphins (Tursiops truncatus)

Suction-cups with embedded acoustic transmitters (“jawphones”) can be used to deliver sound to odontocetes while out of water. When used for electrophysiological hearing tests, both jawphone and recording electrode location are important considerations. This study examined bottlenose dolphin auditory brainstem response (ABR) patterns across jawphone and electrode location. Stimuli were tonebursts with center frequencies of 28–160 kHz. When recorded using an electrode immediately behind the blowhole, ABR peak amplitudes were generally highest when the jawphone was placed on the middle of the mandible and lowest when placed near the tip of the rostrum. However, responses were comparable between the middle and posterior mandible when recorded with an electrode near the auditory meatus. These patterns were consistent across frequency, suggesting that ABRs recorded at the blowhole likely contain more binaural contributions than those recorded at the meatus. While blowhole electrode placements with a jawphone on the middle of the mandible provide the highest signal-to-noise ratios, they may not provide ear-specific information at suprathreshold stimulus levels, which could lead to confusion regarding the optimal location for transmitting sound to the ear. [Funded by US Fleet Forces Command.]

Hearing Assessment in Zebrafish During the First Week Postfertilization.

The zebrafish (Danio rerio) is a valuable vertebrate model for human hearing disorders because of many advantages in genetics, embryology, and in vivo visualization. In this study, we investigated auditory function of zebrafish during the first week postfertilization using microphonic potential recording. Extracellular microphonic potentials were recorded from hair cells in the inner ear of wild-type AB and transgenic Et(krt4:GFP)(sqet4) zebrafish at 3, 5, and 7 days postfertilization in response to 20, 50, 100, 200, 300, and 400-Hz acoustic stimulation. We found that microphonic threshold significantly decreased with age in zebrafish. However, there was no significant difference of microphonic responses between wild-type and transgenic zebrafish, indicating that the transgenic zebrafish have normal hearing like wild-type zebrafish. In addition, we observed that microphonic threshold did not change with the recording electrode location. Furthermore, microphonic threshold increased significantly at all tested stimulus frequencies after displacement of the saccular otolith but only increased at low frequencies after displacement of the utricular otolith, showing that the saccule rather than the utricle plays the major role in larval zebrafish hearing. These results enhance our knowledge of early development of auditory function in zebrafish and the factors affecting hearing assessment with microphonic potential recording.

Effects of Stimulus and Recording Parameters on the Air Conduction Ocular Vestibular Evoked Myogenic Potential

Vestibular evoked myogenic potentials (VEMPs) have been recorded from the sternocleidomastoid muscle (cervical VEMP or cVEMP) and more recently from the eye muscles (ocular VEMP or oVEMP) in response to air conduction and bone conduction stimuli. Both cVEMPs and oVEMPs are mediated by the otoliths and thereby provide diagnostic information that is complementary to videonystagmography and rotational chair tests. In contrast to the air conduction cVEMP, which originates from the saccule/inferior vestibular nerve, recent evidence suggests the possibility that the air conduction oVEMP may be mediated by the utricle/superior vestibular nerve. The oVEMP, therefore, may provide complementary diagnostic information relative to the cVEMP. There are relatively few studies, however, that have quantified the effects of stimulus and recording parameters on the air conduction oVEMP, and there is a paucity of normative data. To evaluate the effects of several stimulus and recording parameters on the air conduction oVEMP and to establish normative data for clinical use. A prospective repeated measures design was utilized. Forty-seven young adults with no history of neurologic disease, hearing loss, middle ear pathology, open or closed head injury, cervical injury, or audiovestibular disorder participated in the study. The effects of stimulus frequency, stimulus level, gaze elevation, and recording electrode location on the amplitude and latency of the oVEMP for monaural air conduction stimuli were assessed using repeated measures analyses of variance in an initial group of 17 participants. The optimal stimulus and recording parameters obtained in the initial group were used subsequently to obtain oVEMPs from 30 additional participants. The effects of stimulus frequency, stimulus level, gaze elevation, and electrode location on the response prevalence, amplitude, and latency of the oVEMP for monaural air conduction stimuli were significant. The maximum N1-P1 amplitude and response prevalence were obtained for contralateral oVEMPs using a 500 Hz tone burst presented at 125 dB peak SPL during upward gaze at an elevation of 30°. The optimal stimulus and recording parameters quantified in this study were used to establish normative data that may be useful for the clinical application of the air conduction oVEMP.

Effect of Stimulus and Recording Parameters on Spatial Spread of Excitation and Masking Patterns Obtained With the Electrically Evoked Compound Action Potential in Cochlear Implants

Spread of excitation within the cochlea in response to electrical stimulation can be measured with the electrically evoked compound action potential (ECAP). Different spread of excitation measurement techniques have been reported in the literature. One method uses a fixed stimulus location while varying the recording electrode along the length of the implanted array. This results in a relatively coarse estimate of spatial spread (SS) along the cochlea. Another method uses a forward-masking paradigm to evaluate the relative overlap of stimulated neural populations between electrodes. Both the probe and recording electrodes are fixed in location while a masker stimulus is systematically applied across electrodes. This method, which yields a more precise estimate of spatial excitation patterns, is termed spatial masking (SM). Five experiments were conducted to examine potential effects of stimulus and/or recording parameters on SS and SM patterns. Experiment 1 examined whether SS patterns were systematically broader than SM patterns across electrodes and subjects. Experiments 2 and 3 evaluated the effects of stimulus level on SS and SM patterns, respectively, to determine whether increased stimulus level systematically resulted in broader patterns. Experiment 4 evaluated whether recording electrode location affected SM patterns, and Experiment 5 evaluated whether SM patterns varied significantly across repeated trials within a test session. Data were collected for 27 ears in 26 adult and teenage subjects (N = 6 ears with Advanced Bionics CII, N = 8 ears with Advanced Bionics HiRes 90K, N = 10 ears with Nucleus 24R[CS], N = 3 ears with Nucleus 24RE[CA] Freedom). A standard forward-masking subtraction paradigm was used for all ECAP measures. For SS patterns, the masker and probe were fixed on the same electrode at the same level while the recording electrode varied across the remaining electrodes in the array. For SM patterns, the probe and recording locations were fixed while the masker location varied across all electrodes except the recording electrode. In experiment 1, SS patterns were broader than SM patterns. Subjects with Advanced Bionics devices exhibited relatively broad patterns for both measures, whereas Nucleus subjects typically exhibited narrower SM functions relative to SS functions. In experiments 2 and 3, there was a significant effect of stimulus level on the spread of both SS and SM patterns in roughly one-third of measures in each experiment. In experiment 4, there was a significant effect of recording electrode location on the width/spread of SM patterns for only 11.5% of comparisons. In experiment 5, there were no significant differences in SM amplitudes across repeated trials for 94% of comparisons, which suggests that ECAP measures are highly robust within a test session. Results showed that SS functions were generally broader than SM functions, which suggests that SS measures reflect volume conduction of the ECAP response along the length of the cochlea. Differences in the spread of SM functions across devices are likely due to differences in modiolar proximity between the respective electrode array designs. Stimulus level had a more significant effect on the spread of SM functions than recording electrode location. Finally, ECAP measures were shown to be highly stable across repeated measurements within a test session; however, repeatability was not assessed across sessions or over extended time intervals.

Hypergravity susceptibility of ventral root activity during fictive swimming in tadpoles (Xenopus laevis).

1. Fictive swimming is an experimental model to study early motor development. As vestibular activity also affects the development of spinal motor projections, the present study focused on the question whether in Xenopus laevis tadpoles, the rhythmic activity of spinal ventral roots (VR) during fictive swimming revealed age-dependent modifications after hypergravity exposure. In addition, developmental characteristics for various features of fictive swimming between stages 37/38 and 47 were determined. Parameters of interest were duration of fictive swimming episodes, burst duration, burst frequency (i.e., cycle length), and rostrocaudal delay. 2. Ventral root recordings were performed between developmental stage 37/38, which is directly after hatching and stage 47 when the hind limb buds appear. The location of recording electrodes extended from myotome 4 to 17. 3. Hypergravity exposure by 3 g-centrifugation lasted 9 to 11 days. It started when embryos had just terminated gastrulation (stage 11/19-group), when first rhythmical activity in the ventral roots appeared (stage 24/27-group), and immediately after hatching (stage 37/41-group). Ventral root recordings were taken for 8 days after termination of 3 g-exposure. 4. Between stage 37/38 (hatching) and stage 47 (hind limb bud stage) burst duration, cycle length and rostrocaudal delay recorded between the 10th and 14th postotic myotome increased while episode duration decreased significantly. In tadpoles between stage 37 and 43, the rostrocaudal delay in the proximal tail part was as long as in older tadpoles while in caudal tail parts, it was shorter. During this period of development, there was also an age-dependent progression of burst extension in the proximal tail area that could not be observed between the 10th and 14th myotome. 6. After termination of the 3 g-exposure, the mean burst duration of VR activity increased significantly (p < 0.01) when 3 g-exposure started shortly after gastrulation but not when it started thereafter. Other parameters for VR activity such as cycle length, rostrocaudal delay and episode duration were not affected by this level of hypergravity. 7. It is postulated that (i) functional separation of subunits responsible for intersegmental motor coordination starts shortly after hatching of young tadpoles; and that (ii) gravity exerts a trophic influence on the development of the vestibulospinal system during different periods of embryonic development leading to the formation of more rigid neuronal networks earlier in the spinal than in the ocular projections.

Dermatomal Somatosensory Evoked Potentials: Methodology and Clinical Applications

Dermatomal somatosensory evoked potentials (DSEPs) have been recently added to the armamentarium of techniques that address segmental level issues of spinal cord and nerve roots. Although DSEPs are technically similar to evoked potential to mixed nerve stimulation, good results depend on attention to factors such as stimulating electrode size and location, recording electrode location, alertness, protocol design, and waveform analysis. DSEPs have been used successfully in single-level and multiple-level root disease and in segmental-level evaluation of spinal cord involvement. Compared to other techniques, DSEPs have been at least as successful in identifying abnormalities, and, in some cases, mo-reso. In fact, for the thoracic levels, DSEPs may be considered a unique noninvasive method.

EEG correlates of hypnotic susceptibility based upon fast Fourier power spectral analysis

The purpose of the present study was to determine if there were differences between high and low hypnotic susceptible subjects based upon fast Fourier power spectral analysis of the EEG recorded both before and during hypnotic tasks from frontal-temporal and occipital-parietal locations. Significant differences were obtained based upon EEG recording electrode location, EEG frequency within six different frequency domains, and hypnotic tasks. However, no main effect differences were obtained based upon hypnotic susceptibility. In contrast to some evoked potential studies in which a few differences have been obtained based on hypnotic susceptibility the lack of any EEG differences in this study even when positive and negative hallucination tasks were employed may have implications for the role of the neocortex in mediating hypnotic phenomena.

The Assumptions of Isochronal Cardiac Mapping

Isochronal maps of cardiac activation are commonly used to study the mechanisms and to guide the ablative therapies of arrhythmias. Little has been written about the assumptions implicit in the construction and use of isochronal cardiac maps. These assumptions include the following: (1) the location of the recording electrodes is known with sufficient accuracy to determine the mechanism of an arrhythmia or to guide therapy; (2) a single, discrete activation time can be assigned to each recording electrode location; (3) the presence or absence of activation at an electrode site can be reliable ascertained, and when activation is present, the time of activation can be determined with sufficient accuracy to specify the mechanism of an arrhythmia or to guide therapy; and (4) the recording electrodes are close enough together that the activation sequence can be estimated with sufficient accuracy to determine the mechanism of an arrhythmia or to guide therapy. The manuscript reviews evidence that these assumptions may not always be true, and when they are not, the isochronal map may be misleading.