Gender and modulation frequency effects on auditory steady state response (ASSR) thresholds

Cortical connectomic mediations on gamma band synchronization in schizophrenia

Aberrant gamma frequency neural oscillations in schizophrenia have been well demonstrated using auditory steady-state responses (ASSR). However, the neural circuits underlying 40 Hz ASSR deficits in schizophrenia remain poorly understood. Sixty-six patients with schizophrenia spectrum disorders and 85 age- and gender-matched healthy controls completed one electroencephalography session measuring 40 Hz ASSR and one imaging session for resting-state functional connectivity (rsFC) assessments. The associations between the normalized power of 40 Hz ASSR and rsFC were assessed via linear regression and mediation models. We found that rsFC among auditory, precentral, postcentral, and prefrontal cortices were positively associated with 40 Hz ASSR in patients and controls separately and in the combined sample. The mediation analysis further confirmed that the deficit of gamma band ASSR in schizophrenia was nearly fully mediated by three of the rsFC circuits between right superior temporal gyrus-left medial prefrontal cortex (MPFC), left MPFC-left postcentral gyrus (PoG), and left precentral gyrus-right PoG. Gamma-band ASSR deficits in schizophrenia may be associated with deficient circuitry level connectivity to support gamma frequency synchronization. Correcting gamma band deficits in schizophrenia may require corrective interventions to normalize these aberrant networks.

Does the location of electrode on tympanic membrane matter when recording electrocochleography?

BACKGROUND

The non-invasive tympanic electrocochleography (TM-ECochG) is useful for clinical diagnoses. Nevertheless, the influence of the electrode location on tympanic membrane (TM) on ECochG results needs to be studied.

OBJECTIVE

The aim of the present study was to compare the TM-ECochG results obtained when the electrode was placed on the superior region versus the inferior region of TM.

MATERIALS AND METHODS

Forty healthy adults (aged 29 to 50 years) participated in this comparative study. The TM-ECochG testing was conducted with the electrode placed on the superior and inferior regions of TM.

RESULTS

SP and AP amplitudes were statistically higher for the inferior region of TM (p < .05). In contrast, SP/AP ratios were comparable between the two regions of TM (p = .417).

CONCLUSIONS AND SIGNIFICANCE

In TM-ECochG recording, when the electrode was placed on the inferior region of TM, SP and AP amplitudes were greater than when the electrode was placed on the superior region of TM. On the other hand, SP/AP amplitude ratio was not affected by the location of electrode on TM. The findings from the present study could be useful to guide clinicians in optimizing TM-ECochG recording when testing their respective patients.

Multichannel search strategy for improving the detection of auditory steady-state response

Auditory steady-state response (ASSR) is useful for hearing threshold estimation. The ASSR is usually detected with objective response detectors (ORD). The performance of these detectors depends on the signal-to-noise ratio (SNR) as well as the signal length. Since it is undesirable to increase the signal length, then, this work provides a multivariate technique for improving the SNR and consequently the detection power. We propose the insertion of a short calibration step before the detection protocol, in order to perform a search among the available electroencephalogram (EEG) derivations and select the derivation with the highest SNR. The ORD used in this work was the magnitude-squared coherence (MSC). The standard detection protocol is to use the same EEG derivation in all exams. Using 22-scalp positions, the new technique achieved a detection rate higher than that obtained in 99.13% of the standard detection protocol. When restrictions were applied to the search, a superior performance was achieved. Thus, the technique proposed was able to track the best EEG derivations before exams and seems to be able to deal with the variability between individuals and between sessions.

Cortical volume and 40-Hz auditory-steady-state responses in patients with schizophrenia and healthy controls

Background

Abnormalities in the 40-Hz auditory steady-state response (ASSR) of the gamma range have been reported in schizophrenia (SZ) and are regarded as important pathophysiological features. Many of the previous studies reported diminished gamma oscillations in SZ, although some studies reported increased spontaneous gamma oscillations. Furthermore, brain morphological correlates of the gamma band ASSR deficits have rarely examined. We investigated different measures of the 40-Hz ASSR and their association with brain volumes and psychological measures of SZ.

Methods

The 40-Hz ASSR was measured for 80 dB click sounds (1 ms, 500-ms trains at 40-Hz, with 3050 to 3500 inter-train interval) using electroencephalography with 64 electrodes in 33 patients with SZ (male: 16, female: 17 (age range: 21–60)) and 30 healthy controls (HCs) (male: 13, female: 17 (age range: 23–64)). Four gamma oscillation measures (evoked power, spontaneous oscillations (baseline and total power), and inter-trial phase coherence (ITC)) were assessed. The source activities of the ASSR were also analyzed. Brain volumes were assessed using high-resolution magnetic resonance imaging and voxel-based morphometry and superior temporal gyrus (STG) volume measures were obtained.

Results

Patients with SZ had larger total and evoked powers and higher ITC than HCs. Both groups showed significantly different association between mean evoked power and right STG volume. In HCs but not SZ, mean evoked power showed significant positive correlation with right STG volume. In addition, the two groups showed significantly different association between verbal fluency and mean evoked power. High evoked power was significantly correlated with poor verbal fluency in SZ.

Conclusions

The current study found increased gamma oscillation in SZ and suggests significant involvement of the STG in gamma oscillations.

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SZ had larger total and evoked powers and higher ITC than HCs.

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Evoked power positively correlated with right STG volume in HCs.

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High evoked power correlated with poor verbal fluency in SZ.

Effects of degree and symmetricity of bilateral spectral smearing, carrier frequency, and subject sex on amplitude of evoked auditory steady-state response signal

The characteristics of an auditory steady-state response (ASSR) signal can be affected by the pathophysiological statuses of the left and right ears, such as a smeared sensation by native spectral smearing owing to sensorineural hearing impairment, because they can affect the perception of the stimulus, the degree of concentration on the stimulus and comfort in concentration. However, to date, few studies have examined the effects of such smeared sensations on the amplitude of the evoked ASSR signal. In this study, we synthesized various auditory stimuli with different degrees of spectral smearing using a hearing loss simulator to match the age of participant groups with different degrees of spectral smearing. We then performed three subjective tests, representing symmetric and asymmetric bilateral spectral smearing, with 16 normal-hearing individuals to observe the effects of the severity and symmetricity of bilateral spectral smearing, the value of the carrier frequency of auditory stimuli, and the sex of the individual on the amplitude in evoked ASSR signals. The experimental results demonstrated the following: (1) the application of spectral smearing to normal sounds may result in amplitude-reduced ASSR signals, (2) the effect of spectral smearing on the amplitude of the ASSR signals is most significant when the degrees of bilateral spectral smearing are asymmetric, (3) the selection of carrier frequency in an auditory stimulus can affect the amplitude of evoked ASSR signals regardless of the degree of spectral smearing, and (4) the sex of the individual can affect the amplitude of the evoked ASSR signal in various test conditions. The results of this study can help estimate the effects of smeared sensation by spectral smearing owing to sensorineural hearing impairment on the amplitude of evoked ASSR signals.

40 Hz Auditory Steady-State Response: The Impact of Handedness and Gender

The 40 Hz auditory steady-state response (ASSR) is a periodic response to a periodic stimulation. Its sources are located in the primary auditory cortex and the asymmetry of the planum temporale has previously been associated with hand preference and gender-related differences; thus subject's handedness and gender could potentially influence ASSRs. Nevertheless, electrophysiological studies of ASSRs are mainly dominated by right-handed participants and the observed findings can only be generalized to the right-handed populations. However, for a potential use of 40 Hz ASSR as a translational biomarker of neuropsychiatric disorders, it is important to investigate the response in association to handedness and gender. We included an equal number of left-handed and right-handed males and females and recorded EEG responses during left-ear, right-ear and both ears stimulation. The results of the study suggest that the processing of 40 Hz auditory stimulation depends on the subjects' gender and handedness: significantly lower phase-locking and strength of 40 Hz ASSRs were observed in left-handed females as compared to left-handed males, but right-handers did not differ in 40 Hz ASSRs. Our observation of the opposite impact of gender in the examined handedness groups stresses the importance of careful consideration of handedness and gender factors when evaluating the determinants of inter individual variability of 40 Hz ASSRs. This finding is of particular importance for clinical studies in psychiatry and neurology.

Electrocochleographic recording in Asian adults: Preliminary normative data and demographic analyses

OBJECTIVE

Electrocochleography (ECochG) is valuable to diagnose Meniere's disease objectively. The aim of the present study was to provide preliminary normative data for ECochG among Asian adults. The influences of ethnicity (Malay versus Chinese) and gender on ECochG results were also studied.

METHODS

Twenty-two Malay adults (10 men and 12 women) and twenty Chinese participants (10 men and 10 women) aged between 20 and 49 years participated in this study. Extratympanic ECochG (ET-ECochG) was recorded according to standard non-invasive procedure. Summating potential (SP) amplitude, action potential (AP) amplitude and SP/AP ratio were analyzed accordingly.

RESULTS

ET-ECochG results were found to be comparable between left and right ears (p > 0.05). No notable differences in ET-ECochG results were found between Malay and Chinese groups (p > 0.05). No significant influence of gender on ET-ECochG outcomes was also noted (p > 0.05). The derived normative data for Asian adults (84 ears) are consistent with previous reports.

CONCLUSION

The present study provides preliminary normative data for ET-ECochG among Asian adults. The ECochG components do not appear to be influenced by either ethnicity or gender. The derived normative data can be used for clinical applications and as the reference for future studies involving Asian population.

Mode of recording and modulation frequency effects of auditory steady state response thresholds

INTRODUCTION

The performance of auditory steady state response (ASSR) in threshold testing when recorded ipsilaterally and contralaterally, as well as at low and high modulation frequencies (MFs), has not been systematically studied.

OBJECTIVE

To verify the influences of mode of recording (ipsilateral vs. contralateral) and modulation frequency (40Hz vs. 90Hz) on ASSR thresholds.

METHODS

Fifteen female and 14 male subjects (aged 18-30 years) with normal hearing bilaterally were studied. Narrow-band CE-chirp^® stimuli (centerd at 500, 1000, 2000, and 4000Hz) modulated at 40 and 90Hz MFs were presented to the participants' right ear. The ASSR thresholds were then recorded at each test frequency in both ipsilateral and contralateral channels.

RESULTS

Due to pronounced interaction effects between mode of recording and MF (p<0.05 by two-way repeated measures ANOVA), mean ASSR thresholds were then compared among four conditions (ipsi-40Hz, ipsi-90Hz, contra-40Hz, and contra-90Hz) using one-way repeated measures ANOVA. At the 500 and 1000Hz test frequencies, contra-40Hz condition produced the lowest mean ASSR thresholds. In contrast, at high frequencies (2000 and 4000Hz), ipsi-90Hz condition revealed the lowest mean ASSR thresholds. At most test frequencies, contra-90Hz produced the highest mean ASSR thresholds.

CONCLUSIONS

Based on the findings, the present study recommends two different protocols for an optimum threshold testing with ASSR, at least when testing young adults. This includes the use of contra-40Hz recording mode due to its promising performance in hearing threshold estimation.