Wave I in brain-stem response audiometry arises from?
Cochlear nerve
Superior olivary complex
Lateral lemniscus
Inferior colliculus
Ans. is 'a' i.e., Cochlear nerve Brain Stem Response Audiometry (BERA) It is a non-invasive procedure which objectively helps to find the integrity of central auditory pathway through the VIII nerve, pons and mid brain. It is accurate to within 10 or 15 dB of the psychoacoustic thereshold. It is the most reliable audiological method of differentiating between cochlear and Retrocochlear hearing losses. It is an objective test and can be done under sedation. It is used both as a screening test and as a definative hearing assessment test in children. Best test to detect deafness in infants (reliably recorded even from premature infants of 30 weeks gestational age) and mentally retarded or malingering subjects. It is also used for Identification of the site of lesion in Retrocochlear pathologies and to diagnose brainstem pathology e.g. multiple sclerosis or pontine tumor. Waves of BERA In a normal person, 7 waves are produced in first 10 miliseconds. The first, third and fifth waves are most stable and are used in measurements. Site of origin of waves are :- Wave I Distal pa of Eighth nerve Wave II Proximal, pa of Eighth cranial nerve Wave III Cochlear nucleus Wave IV Superior olivary complex Wave V Lateral leminiscus Wave VI & VII Inferior colliculus