Objective: It is easier for a listener to detect a brief tonal signal presented in a longer masking noise by increasing the delay between the signal and the masker. This phenomenon (overshoot) is influenced by a reduction in cochlear amplification and to date, there is no objective tool to investigate it. Therefore, a different paradigm of the auditory brainstem response (ABR) was utilized to measure auditory overshoot. It was assumed that increasing the delay onset time (DOT) between a signal and a masker reduces the latencies of waves I and III. Materials & Methods: Sixteen normal young male guinea pigs were tested. A tone burst stimulus (signal: 16 kHz, 5ms in duration) and wide-band noise (masker: 0. 1-8. 0 kHz, 100ms in duration) at three DOTs were used. To diminish the effect of the noise on waves, waveforms were subtracted from those derived from the noise burst alone. The absolute latency of the waves I and III, inter-peak latency of the waves I-III, and amplitude ratio of the waves III/I were compared for the 0, 30, and 100ms DOTs and five signal-to-noise ratios. Results: The latencies of increased from the 0 to 30ms DOT and then decreased from the 30 to 100ms DOT (p < 0. 001). No significant changes were observed in the latency waves at the 100ms DOT compared to the 0ms DOT (p > 0. 005). Moreover, there were no significant differences between the three DOTs regarding the inter-peak latency and amplitude ratio of the waves (p <0. 005). Conclusion: The study results showed an overshoot-like electrophysiological effect using ABR. Therefore, an objective test was used to investigate auditory cochlear gain.

Objective Dyslexia is a neurological dysfunction (also known as a learning disability) that characterized by disability in reading in spite of normal intelligence. Bothe genetic and environmental risk factors are contributing into the condition.Diagnosis of dyslexia is based on examination and investigation of the patient’s memorial, spelling, visual, and reading skills. It is the most common learning disability, affecting 3%–0% of the school population. Modern neuroimaging techniques such as functional magnetic resonance imaging (fMRI) have shown a correlation between both functional and structural differences in the brains of children with reading difficulties. Hence, to address this issue, the auditory brainstem responses of children with dyslexia were investigated.Materials & Methods Fifty two children with dyslexia (30 males, 22 females) were selected after examination by speech therapist. In addition, fifty two control children were included as well. The IPSI and contralateral ABR tests were conducted on both cases and controls. Click stimuli were used at 75 nHL intensity. The study focused on absolute latency of wave V in both groups.Results Absolute latency of wave V in contralateral showed differences between children with dyslexia and control group, but no significant results were found in IPSI testing.Conclusion The current data provide an evidence for brainstem and its function in signal processing and the role of brainstem nucleus on processing and delivering the information to each hemisphere.

To evaluate the changes of ABR values in hyperbilirubinemic newborns, 85 cases with severe jaundice (total bilirubin levels over 16 mg/dL and direct bilirubin less than 2 mg/dL) were selected from those admitted to Children's Medical Center by simple sampling method. These infants had no other problem except jaundice. ABR was taken before treatment in all cases and in some (10 cases) after exchange transfusion or phototherapy as treatment modalities. 41 neonates (48%) had abnormal ABR values, such as increased hearing threshold, prolonged latencies of waves I, III & V (p- value<0.05), prolonged interpeak latencies of I-V & 111-V (p-value<0.05), absence of waves and abnormal wave morphology. These findings could be indicative of both peripheral (8th nerve) and brain stem disturbances. After treatment ABRs showed improvement in some aspects, such as latencies of waves I, III & V (p value<0.05), but not in interpeak latencies (I-Ill, III-V & I-V) and hearing thresholds. In accordance with previous studies, there was no association between serum total bilirubin concentration and ABR test results. This could be interpreted as low significance of serum total bilirubin as a criterion for early prediction of bilirubin induced encephalopathy.