CENTRAL MECHANISMS--CELLULAR GENERATORS OF EVOKED RESPONSES

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The brainstem auditory evoked potential (BAEP) is a response to a transient acoustic stimulus, and reflects the activity of cells in the auditory nerve and brainstem. Because it can be measured from the surface of the head, the BAEP provides a noninvasive monitor of lower auditory system function. Although the BAEP is routinely used clinically, the cellular mechanisms by which it is generated are not yet understood. Our goal is to develop a model for the generation of the cat BAEP based at the cellular level. Toward that goal, we propose to model the production of potential fields by individual discharging cells. We will formulate a cell model to describe how transmembrane currents are generated by a discharging neuron, and a head model to describe the potential distribution produced by those currents. The models will be implemented for cat; the cell model will be implemented for various auditory brain-stem neurons. Available values for cell and head-model parameters will be used in the implementations, and experiments will be performed to determine the remaining parameter values. Potential distributions produced by known current sources placed in the heads of anesthetized cats will be measured; head-model parameter values will be adjusted so that potentials calculated from the head model fit the measurements. Potentials produced by individual discharging auditory brainstem neurons will be measured using the method of spike-triggered averaging; cell-model parameter values will be adjusted so that potentials calculated using the cell and head models match measured potentials. An overall theory for the BAEP will place clinical and research applications on a far sounder basis than is obvious at present and will suggest hosts of new practical uses.