Reproducibility of Test-Retest Cortical Evoked Responses in Patients with Focal Epilepsy

This exploratory study examined the short-term reliability of cortical auditory evoked responses recorded from patients undergoing whole-head scalp elec-troencephalography (EEG) monitoring to assess their candidacy for surgical treatment of intractable focal seizures. Participants were 26 patients with either left-sided (N = 13) or right-sided focal epilepsy admitted to the hospital for continuous scalp EEG monitoring for possible epilepsy surgery planning. Cortical auditory evoked responses were recorded over multiple days from scalp EEG electrodes using tones presented binaurally in a passive oddball paradigm. Test-retest intervals were 1 - 6 days (mean 2 days). Test-retest reproducibility of the auditory N1 response was assessed by paired t-test (latency) and cross-correlation analysis (amplitude and latency). Within-patient comparisons of test-retest auditory N1 peak latencies revealed no significant differences. The cross-correlation coefficient indicated high test-retest reproducibility of the N1 waveform (rcc = 0.88). Seizure lateralization was not associated with asymmetries in N1 latencies or amplitudes. An N1 amplitude asymmetry (right > left) in patients with focal seizures originating from the left hemisphere was initially observed, but disappeared when patients with prior resections were excluded, suggesting that reduced left hemisphere tissue volume may account for the smaller N1 amplitudes. Test-retest reliability of cortical auditory evoked responses was unexpectedly high in patients with focal epilepsy regardless of seizure lateralization or localization. These findings challenge the view that neural responses are intrinsically unstable (unreliable) in patients with seizures.

Auditory steady-state evoked response in diagnosing and evaluating hearing in infants

BACKGROUND: Auditory steady-state evoked response (ASSR) is one of the new objective electrophysiological methods to test hearing in infants. It can provide a reliable and complete audiogram with specific frequency to help the hearing diagnosis and rehabilitation of hearing and languaging following auditory screening. OBJECTIVE: To compare the response threshold of ASSR with auditory threshold of visual reinforcement audiometry (VRA) in infants failed in the hearing screening for investigating their hearing loss. DESIGN: A comparative observation. SETTINGS: Maternal and child health care hospitals of Guangdong province, Shunde city, Nanhai city and Huadu district. PARTICIPANTS: Totally 321 infants of 0-3 years undergoing ASSR test were selected from the Hearing Center of Guangdong Maternal and Child Health Care Hospital from January 2002 to December 2004. Informed consents were obtained from their guardians. There were 193 cases (60.2%) of 0-6 months, 31 cases (9.7%) of 7-12 months, 17 cases (5.3%) of 13-18 months, 14 cases (4.4%) of 19-24 months, 33 cases of 25-30 months, and 33 cases (10.2%) of 31-36 months. METHODS: ① The 321 infants failed in the hearing screening were tested under sleeping status, the ranges of response threshold distribution in ASSR of different frequencies were analyzed in each age group. ② The infants above 2 years old were also tested with VRA, and their response thresholds were compared between VRA and ASSR. ③ Evaluative standards: The response threshold was < 30 dB for normal hearing, 31-50 dB for mild hearing loss, 51-70 dB for moderate hearing loss, 71-90 dB for severe hearing loss, and > 91 dB for extremely severe hearing loss. MAIN OUTCOME MEASURES: ① ASSR results of the infants failed in the screening; ② Proportion of cases of each response threshold in each age group; ③ Comparison of ASSR response thresholds and VRA auditory thresholds in the infants of 2-3 years old. RESULTS: ①The response threshold was < 30 dB in 47.4% of the 321 infants failed in the initial hearing screening and secondary screening after 42 days. ② Severe to extremely severe hearing loss was detected in only 16 cases (8.3%) of the 193 infants of 0-6 months, in 9 cases (27.3%) of the 33 infants of 25-30 months, and 13 cases (39.4%) of the 33 infants of 31-36 months. Of the 193 infants of 0-6 months old who failed in the initial screening and the second screening after 42 days, the ASSR auditory threshold was < 30 dB in 97 cases (50.26%), 31-50 dB in 63 cases (32.6%), 51-70 dB in 17 cases (8.8%), 71-90 dB in 7 cases (3.6%), and > 91 dB in 9 cases (4.7%). ③ Among the 321 infants failed in the screening, the auditory threshold in the 6 age groups was < 30 dB in 47.4%, 31-50 dB in 27.1%, 51-70 dB in 8.4%, 71-90 dB in 6.2%, and > 91 dB in 10.9%. ④ The difference between ASSR response threshold and VRA auditory thresholds was 6-18 dB in the normal hearing group, mild and moderate hearing loss groups, and there was high correlation between them. The difference of ASSR and VRA thresholds was less than 5 dB between extremely severe and severe hearing loss groups, 5-13 dB between extremely severe and moderate-to-severe hearing loss groups (P < 0.05), and there was no significant differences between severe and moderate-to-severe hearing loss groups (P > 0.05). CONCLUSION: ① The hearing was normal in about half of the infants, although they failed in the primary screening and secondary screening. ② The proportion of the severity of hearing loss was increased along with aging. ③ Mild and moderate hearing losses are dominant in infants. ④ ASSR is reliable to evaluate the hearing of infants.

Evaluation of SON’OR^(█),a Medical Device for Provoked Otoacoustic Emissions and Brainstem Evoked Response Audiometry Made in Cameroon

Background: There is a huge gap in the audiological care in Africa by comparison with Western countries. Its main reason is the prohibitive cost of the medical devices used to screen or diagnose patients. A Cameroonian team tackled this problem by developing a medical device (SON’OR&copy;) which integrates a new instrumentation amplifier structure dedicated to perform otoacoustic emissions (OAE) and brainstem evoked response audiometry (BERA). The major technical challenges to perform OAE and BERA are the synchronization and the amplification of signals of very low amplitude. In this work, we emphasize on the general criteria necessary and indispensable to achieve an optimal amplification. The application of a novel instrumentation amplifier structure characterized by its optimized noise factor in the case of BERA and OEA emissions provides simulations and experimental results fully in line with forecasts. The design of SON’OR&copy;is based on general techniques of electronic instrumentation to which we associated the new instrumentation amplifier structure. Objective: To report the clinical evaluation of SON’OR&copy;as a screening and diagnostic tool. Methods: We conducted a cross sectional comparative study in Centre Hospitalier d’Essos in Yaoundé. We tested SON’OR&copy;on two sets of subjects, one for OAE with OTODYNAMICS Echoport ILO 292-II as gold standard and the other for BERA with NEUROSOFT NEURO AUDIO&copy;as gold standard. Each patient was tested with both devices and then we studied the inter device differences and calculated the sensitivity, specificity, positive predictive value and negative predictive value for each test. Results: We got 52 subjects for OEA and 51 for BERA testing. Sex ratio was 1 woman for 2 men in both groups. Mean age was 24.86(SD = 10.53) and 26.33 (10.55) for OAE and BERA groups respectively. SON’OR&copy;had good performances, showing sensitivity of 92.85%/95%, specificity of 96.77%/90.47%, positive predictive value of 95.21%/93.44% and negative predictive value of 95.23%/92.68% for OAE/ BERA respectively. Conclusion: SON’OR&copy;has good characteristics as a medical diagnostic tool. Furthermore its stability and performances in poor electrical conditions make it a robust device really suited for resource limited settings.

SATURATION DIVING WITH HELIOX TO 350 METERS OBSERVATION ON HEARING THRESHOLD, BRAINSTEM EVOKED RESPONSE AND ACOUSTIC IMPEDANCE

Four divers were compressed to 350 m to observe changes in hearing threshold, brainstem evoked response and acoustic impedance. The divers experienced no tinnitus, impairment of bearing, earache daring compression. Examination showed that the threshold of tower frequency range of hearing was elevated because of the masking effect of the noise in the hyperbaric chamber. Changes in waveform and latency of brainstem evoked response were due to changes in sound wave transmission affected by the chamber pressure and a poor ratio of signal to noise in the hyperbaric environment with heliox. All these changes were transient After leaving the chamber, the hearing threshold and brainstem evoked response returned to normal. Besides, there were no changes in tympanogram, acoustic compliance and stapedius reflex before and after diving. This indicated the designed speed of compression and decompression in the experiment caused no damage to the divers' acoustic system, and the functions of their Eustachain tubes, middle and inner ears were normal during the diving test

Acoustic Trauma of Guinea Pigs Caused by ^(60) Cobalt γ-Ray

Auditory cortical cvokod rcsponse(ACER) and auditory brainstom cvoked response (ABR) were recorded in guinea pigs before and after irradiation of ^(60)Co γ-ray. A single dose of irradiation on head was 90Gy and 70Gy in two groups, respectively. Two h after irradiation. the threshold shift was 12. 5 dB and 9 dB, and the ACER post-irradiation amplitude ex- ceeded the maximum pre-irradiation value by 20% and 37%. Six h after irradiation, the threshold shift increased to 37 dB and the maximum amplitnde decreased to the level of pre-irradiation in 70Gy-group. In another group, right auditory bulla arca was irradiated with a total dose of 45Gy in a course of six fractions/two weeks. Fourteen d after irradiation, the threshold shift of ABR was 118 dB and the latency of wave I was longer. The amplitude-intensity curve was after irradiation. Histological observation using scanning showed that only outer hair- cells in the basal coil of the cochlea were 6 h after irrdiation 50Gy-group. Bul 16 h later, outer, hair cells in all coils of the cochlea were found to be destroyed extensively and inner cells were destroyed slightly. In 45Gy-group, 14 d after irradiation, outer hair cells in all coils of the cochlea were damaged and no inmer hair cell was injured severely.

THE GENETIC-INDUCED HEARING lOSS CAN BLOCK THE EFFECT OF NOISE TRAUMA IN WAlTZING GUINEA PIG

The waltzing guinea pig may be a good model to investigate if genetic factor can change the sensitivity in noise-induced hearing loss. A total of 34 waltzig guinea pigs were studied and we found that there is no any significant increased sensitivity to noise trauma if the age-induced hearing loss was considered in waltz-ing guinea pig.

Frequency Following Response of Speech-ABR by Instantaneous Energy Spectrum

A frequency following response(FFR) of speech auditory brainstem response(speech-ABR) elicited by the speech syllable/da/contains three distinct waves named as D, E and F, corresponding to the structure of the stimulus sound. The detection and characterization of FFRs are critical in the study and application of speech-ABRs. Conventional methods detect the latencies of the waves in time domain by measuring the maximal amplitudes of the waveform in the preset windows, which suffers the problem of low quality of FFR waves. In this paper, we defined an instantaneous energy(IE) spectrum based on empirical mode decomposition(EMD)method(EMD-IE method) to detect FFR and measured the latencies of the waves. The results reveal that the FFRs are mostly evident on the second layer of the IE spectra,which would benefit the detection and measurement of the FFRs in clinic.

Changes of summating potentials and morphology in theguinea pig cochlea during anoxia

The dynamic changes in CAP, and EP in the scale media were examined with single micropipet during anoxia and reventilation with oxygen. Also, the morphologic changes in IHC, OHC and synapse were observed in this experiment. It was found that the amplitude of SP and EP values declined with alteration in polarity of these value. The changes in polarity and amplitude of SP followed the changes of CAP threshold induced by anoxia. The histologic examinations revcaled no cvidence of acetylcholinesterase (AChE) alteration in the synapse and no succinict dehydrogenase (SDH) changes in IHC appeared. However, the activity of SDH in the OHC decreased. The results suggest that the polarity and amplitude of SP were influenced passively by the changes of EP value. In addition, the change of SP polarity from positive tonegative during anoxia is due to the loss of mudulation process of OHC to IHC, while the SP polarity from negative to positive during the supply of oxygen is caused by regain of the modulation process of OHC.

Effects of delayed brain-derived neurotrophic factor application on cochlear pathology and auditory physiology in rats

Background The development and maintenance of spiral ganglion cells （SGCs） appear to be supported by neurotrophins Removal of this support leads to their gradual degeneration. Intracochlear infusion with neurotrophins can provide trophic support to SGCs in animal deafness models if given shortly after deafening. However, it is not known whether delayed intervention will provide similar protection, which might be clinically relevant. The present research was conducted to determine the effects of brain-derived neurotrophic factor （BDNF） administration on the capacity of the peripheral processes to resprout. Methods The left cochlea of 20 profoundly deafened rats, which were divided into 2 groups equally, was implanted with an electrode and drug-delivery system 30 days after deafening. Either BDNF or artificial perilymph （AP） was delivered continuously for 28 days. Electrically evoked auditory brainstem responses （EABRs） were recorded during the period. SGC body and peripheral process density were measured. Results The EABR thresholds of AP increase continually. Those of BDNF increase slowly at the beginning then decrease, and were significantly less than those of the AP group from day 14 to 28 （P 〈0.01）. In terms of SGC and peripheral process density, the difference between the treated and control ears of BDNF group was clearly significant （P 〈0.01）, but not in AP group （P 〉0.05）. Analysis of the left cochlea between the two groups demonstrated that SGC/peripheral process density of the BDNF group was significantly greater than that of the AP group. Finally, a functional formula was developed relating the last EABR threshold and SGC density and process density, which was as follows： T= 466.184-2.71 （F.B.L）. Conclusions Under the conditions of delayed intervention following 30 days after deafening in rats, it can be concluded that BDNF enhances SGC bodies and peripheral processes survival after differentiation and so improves auditory sensitivity. SGC peripheral processes influence the auditory sensitivity.