Analysis of cat multichannel acoustic brain-stem response data using dipole localization methods.

We have used dipole localization methods (DLMs) to examine multielectrode acoustic brain-stem response (ABR) data for 9 data files collected in 5 experiments on 2 cats. The analytical model for scalp surface voltage consisted of a single current dipole in a homogeneous spherical head model. DLM sources were compared to ABR generator sites determined in intracranial and lesion experiments described in the literature. DLM source along the mediolateral axis is consistent with a predominantly ipsilateral cochlear nucleus origin for P2, and a predominantly contralateral origin for P3. DLM source for P4 and P5 was near the midline plane, consistent with the suggestion of sources arrayed along both sides of the midline. Average DLM source position increased by 7.1 mm superiorly from P3 to P5, nearly what would be expected from movement from superior olive to inferior colliculus levels. A lack of DLM source movement in the postero-anterior direction is attributed to limitations of the spherical model. The overall progression of mean DLM equivalent source position at successive ABR peaks demonstrates the existence of substantive information about generator source position in scalp surface ABR field patterns. However, model constraints of available DLM techniques present severe restrictions on the physiological interpretation of results.