الفهرس 
Introduction and rationaleOnly 14 pages are availabe for public view
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Abstract
Introduction: AEPs are very small electrical potentials originated from the brain and recorded from the scalp in response to auditory stimuli. Those represent an ideal tool for prediction of hearing in difficult to test individuals (infants, developmentally delayed children, autistic individuals, multiply handicapped children and adults). ABR is the most commonly used AEPs in clinical practice to predict hearing sensitivity using either click or brief tones. However, ABR has subjective interpretation and cannot differentiate between severe and profound hearing losses (upper limit for presentation level in most clinically available ABR equipment is 90 dBnHL). ASSR has been developed as an alternative frequency specific AEPs approach to quantify hearing loss whose constituent discrete frequency components remain constant in amplitude and phase over an infinitely long time period. The stimuli used to evoke ASSR are modulated tones which are frequency specific due to the fact that spectral energy is contained only at frequency of the carrier tone and the frequency of the modulation. These responses are exactly locked to the stimulus rate; they are best detected after the recording has been transferred to the frequency domain. The most prominent responses occur at rates near 40 Hz and 90 Hz. The 40 Hz responses are probably generated by interactions between the thalamus and auditory cortices, whereas the main generators of the 90 Hz responses are probably located in the brainstem. The 40-Hz response is decreased by sleep and anesthesia, whereas the 90 Hz response remains stable. It is an objective test in recording and interpretation (neither the patient respond subjectively nor the clinician make subjective interpretation of the response as being present or absent). So ASSR is used for evaluating threshold as well as suprathreshold levels and can be useful in selection and monitoring of hearing aid fitting and studying disorders in auditory perception. The continuous nature of the stimuli used to elicit the response provides threshold information at intensity levels of 120 dB and higher. Aim of work: The aim of the present study is to provide sufficient information from the published literature on the different clinical uses and advantages of ASSR in audiological practice. Conclusions: ASSRs have less normative and clinical data available than for tone-ABRs. Its use for the site-of-lesion testing is limited due to uncertainties about the specific regions of the brain responsible for generating ASSR. It cannot differentiate between hearing losses of peripheral (cochlear origin) and those due to retrocochlear disorder. It is time consuming procedure as there is need for a long time to make sure that the response stays for several recording sweeps.