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Objectives: To investigate the influence of gender on subcortical representation of speech acoustic parameters where simultaneously presented to both ears., Methods: Two-channel speech-evoked auditory brainstem responses were obtained in 25 female and 23 male normal hearing young adults by using binaural presentation of the 40 ms synthetic consonant-vowel/da/, and the encoding of the fast and slow elements of speech stimuli at subcortical level were compared in the temporal and spectral domains between the sexes using independent sample, two tailed t-test., Results: Highly detectable responses were established in both groups. Analysis in the time domain revealed earlier and larger Fast-onset-responses in females but there was no gender related difference in sustained segment and offset of the response. Interpeak intervals between Frequency Following Response peaks were also invariant to sex. Based on shorter onset responses in females, composite onset measures were also sex dependent. Analysis in the spectral domain showed more robust and better representation of fundamental frequency as well as the first formant and high frequency components of first formant in females than in males., Conclusions: Anatomical, biological and biochemical distinctions between females and males could alter the neural encoding of the acoustic cues of speech stimuli at subcortical level. Females have an advantage in binaural processing of the slow and fast elements of speech. This could be a physiological evidence for better identification of speaker and emotional tone of voice, as well as better perceiving the phonetic information of speech in women., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

The possible role of cochlear function in tinnitus generation is still a matter of debate. To assess the role of outer hair cell dysfunction in tinnitus and its possible relationship with ultra-high frequency (UHF) hearing sensitivity, transient evoked otoacoustic emissions (TEOAE) and UHF hearing thresholds were investigated in normal hearing individuals with and without tinnitus. Eighteen individuals with tinnitus and 22 without tinnitus participated in this study. TEOAE was recorded with click stimulus at 80 dBpeSPL. UHF pure tone audiometry was performed at 10, 12.5, 16, and 18 k Hz. The individuals with tinnitus had significantly poorer UHF hearing sensitivity compared to the control group at 12.5 and 18 k Hz (p<0.048). TEOAE was significantly abnormal in 72.2% of the tinnitus, and 18.2% of the control groups (p=0.001). 'There was a stronger correlation between increasing UHFs hearing threshold and decreasing SNRs of TEOAEs in the tinnitus group compared to the controls. The results support the deafferentation hypothesis, which suggests that the cochlear damage triggers tinnitus incidence, even in patients with normal hearing sensitivity on conventional audiometry, and considers a deafferentation as the underlying cause that elicits central reorganization and eventually leads to tinnitus. The deafferentation hypothesis provides a rationale for performing UHF threshold and OAE assessments in subjectively normal hearing patients with tinnitus. Our study revealed poorer UHF hearing thresholds and more TEOAE abnormalities in normal hearing individuals with tinnitus compared to the controls. Perhaps the alterations in the basal cochlea, following a decrease in UHF hearing sensitivity, affect OAEs that are originated from more apical cochlear parts in tinnitus ears more than non-tinnitus ears. [ABSTRACT FROM AUTHOR]

Tinnitus can cause functional or even structural changes at cortical regions. Given the possible role of the inferior colliculus (IC) in tinnitus due to the distribution of lateral inhibition and receiving input from top-down pathways, we investigated whether tinnitus can also affect subcortical regions, mainly the IC. Auditory brainstem responses to click (cABR) and speech stimuli (sABR) were recorded in 18 individuals with tinnitus and 22 controls without tinnitus matched based on their ages and genders. All subjects had normal hearing sensitivity. Latencies of cABR in waves V and Vn, as well as interpeak latencies (IPLs) of III-V and I-V were significantly longer in individuals with tinnitus compared to the controls. Individuals with tinnitus presented significantly longer latencies of all sABR waves than the control group. The tinnitus patients also presented significant decrease in the amplitude and slope of the V-A complex and declined encoding of the first and higher formants. A combination of bottom-up and top-down processes were involved in the impaired timing in the individuals with tinnitus. The deficits in the auditory processing at the subcortical level (presumably the mi dBrain) could be caused by abnormal bottom-up inputs (i.e. those from more peripheral auditory structures) or abnormal top-down inputs (i.e. abnormal modulations from more central structures through efferent pathways. As a main possible generator of late waves of cABR and all waves of sABR is the IC, these findings indicate that the subcortical regions, particularly the IC, may undergo maladaptive plasticity following tinnitus. The consistency between the results of cABR and sABR indicated that tinnitus might affect the processing of simple and complex stimuli in the same manner. [ABSTRACT FROM AUTHOR]

Tailor-made notched music training (TMNMT) is a novel treatment approach that aims to reverse maladaptive plasticity by inducing lateral inhibition (LI) at the level of the auditory cortex. By considering the possible role of the inferior colliculus (IC) in tinnitus due to the distribution of LI and receiving input from top-down pathways, it has been hypothesized that the short-term application of TMNMT can also reverse maladaptive subcortical plasticity resulting from tinnitus. Auditory brainstem responses' to complex stimuli (cABR) were recorded in nine normal-hearing individuals with tinnitus (4 males). The TMNMT was accomplished compressively during 5 contiguous days. The effects of shortterm intensive TMNMT on the cABR component, tinnitus loudness, and tinnitus handicap inventory (THI) scores were investigated. The latency of cABRs in wave V (p=0.041) was shorter after music training than before, however, there was no significant difference in other components of cABR (p>0.086). There was a significant difference in visual analog scale (p=0.027) and loudness matching (p=0.011) measurements before versus after TMNMT. No significant difference was observed in THI scores (p=0.307) before and following the musical intervention. 'Tire possible explanation for cABR changes following TMNMT is the reverse hierarchy theory (RHT). The RHT argues that top-down processes can influence neural encoding at the level of the brainstem and therefore sensory processing. Following frequent exposures, the higher levels which generally receive input from lower levels will also affect the encoding of stimuli by lower levels. This finding indicated prompt neural reorganization of the brainstem in tinnitus patients with exposure to TMNMT. It seems that TMNMT may partially reverse maladaptive plasticity at the subcortical level; however, the recovery was partial. [ABSTRACT FROM AUTHOR]