THE BRAINSTEM EVOKED AUDITORY RESONSE

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The sound evoked potentials that can be recorded from the scalp are becoming of increasing importance in the clinical diagnosis of various diseases affecting the central nervous system such as tumors and multiple sclerosis. In particular, the so-called short latency components (brainstem auditory evoked potentials, BSEP) have proven to be very useful in making such diagnoses. The use of this method in precise site-of-lesion testing is, however, hampered by uncertainty as to the exact location of the neural generators of the various components of the response. The aim of this study is to obtain a better understainding of the sources of the farfield electrical events that can be recorded from the scalp during the first 10 msec after the onset of a transient sound and to identify the neural generators of these potentials. This will be done through intracranial recordings in humans during neurosurgical operations and in animal experiments. Selective recordings from different brain nuclei will be made in both the human and animal experiments. The likelihood of a certain nerve tract or nucleus being the generator of certain parts of the scalp-recorded BSEP will be studied by determining the amplitude of the response and the anatomical extension of the generator. Experiments will be performed in baboons where the effect of pulsatile pressure on different parts of the auditory nervous system will be studied using implantable balloons. The dependence of the response on different types of stimuli will be explored in order to find optimal stimuli for different types of studies. A better understanding of the origin of these potentials and their dependence on stimulus parameters will increase the cllnical value of this test method and broaden its use in differential diagnosis of disorders afflicting the auditory nervous system.