Auditory brainstem response

The auditory brainstem response (ABR) is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp. The measured recording is a series of six to seven vertex positive waves of which I through V are evaluated. These waves, labeled with Roman numerals in Jewett and Williston convention, occur in the first 10 milliseconds after onset of an auditory stimulus. The ABR is considered an exogenous response because it is dependent upon external factors. The auditory brainstem response (ABR) is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp. The measured recording is a series of six to seven vertex positive waves of which I through V are evaluated. These waves, labeled with Roman numerals in Jewett and Williston convention, occur in the first 10 milliseconds after onset of an auditory stimulus. The ABR is considered an exogenous response because it is dependent upon external factors. The auditory structures that generate the auditory brainstem response are believed to be as follows: In 1967, Sohmer and Feinmesser were the first to publish ABRs recorded with surface electrodes in humans which showed that cochlear potentials could be obtained non-invasively. In 1971, Jewett and Williston gave a clear description of the human ABR and correctly interpreted the later waves as arriving from the brainstem. In 1977, Selters and Brackman published landmark findings on prolonged inter-peak latencies in tumor cases (greater than 1 cm). In 1974, Hecox and Galambos showed that the ABR could be used for threshold estimation in adults and infants. In 1975, Starr and Achor were the first to report the effects on the ABR of CNS pathology in the brainstem. Long and Allen were the first to report the abnormal brainstem auditory evoked potentials (BAEPs) in an alcoholic woman who recovered from acquired central hypoventilation syndrome. These investigators hypothesized that their patient's brainstem was poisoned, but not destroyed, by her chronic alcoholism. Long, K.J.; Allen, N. (October 1984). 'Abnormal brain-stem auditory evoked potentials following Ondine's curse'. Arch. Neurol. 41 (10): 1109–10. doi:10.1001/archneur.1984.04050210111028. PMID 6477223. When interpreting the ABR, we look at amplitude (the number of neurons firing), latency (the speed of transmission), interpeak latency (the time between peaks), and interaural latency (the difference in wave V latency between ears). The ABR represents initiated activity beginning at the base of the cochlea and moving toward the apex over a 4ms period of time. The peaks largely reflect activity from the most basal regions on the cochlea because the disturbance hits the basal end first and by the time it gets to the apex, a significant amount of phase cancellation occurs. The ABR is used for newborn hearing screening, auditory threshold estimation, intraoperative monitoring, determining hearing loss type and degree, and auditory nerve and brainstem lesion detection, and in development of cochlear implants. One use of the traditional ABR is site-of-lesion testing and it has been shown to be sensitive to large acoustic tumors. However, it has poor sensitivity to tumors smaller than 1 centimeter in diameter. In the 1990s, there were several studies that concluded that the use of ABRs to detect acoustic tumors should be abandoned. As a result, many practitioners only use MRI for this purpose now. The reason the ABR does not identify small tumors can be explained by the fact that ABRs rely on latency changes of peak V . Peak V is primarily influenced by high-frequency fibers and tumors will be missed if those fibers aren't affected. Although the click stimulates a wide frequency region on the cochlea, phase cancellation of the lower frequency responses occurs as a result of time delays along the basilar membrane. If a tumor is small, it is possible those fibers won't be sufficiently affected to be detected by the traditional ABR measure. Primary reasons why it is not practical to simply send every patient in for an MRI are the high cost of an MRI, its impact on patient comfort, and limited availability in rural areas and third-world countries. In 1997, Dr. Manuel Don and colleagues published on the Stacked ABR as a way to enhance the sensitivity of the ABR in detecting smaller tumors. Their hypothesis was that the new ABR-stacked derived-band ABR amplitude could detect small acoustic tumors missed by standard ABR measures. In 2005, he stated that it would be clinically valuable to have available an ABR test to screen for small tumors. In a 2005 interview in Audiology Online, Dr. Don of House Ear Institute defined the Stacked ABR as '..an attempt to record the sum of the neural activity across the entire frequency region of the cochlea in response to a click stimuli.'