Real time mapping of rat midbrain neural circuitry using auditory evoked potentials

Auditory evoked potentials were recorded in 360 homogeneously spaced sites, in a volume encapsulating the lateral lemniscus-inferior colliculus transi tion of anaesthetized rats, in order to calculate the electric field vector distribution with each moment in time referenced to the onset of sound pre sentation. Software. to conduct calculations and graphical representation, and hardware, to minimize neural damage upon recording, were developed in o ur laboratory. Our results indicate a smooth transition of both amplitude a nd direction of vectors, suggestive of sequentially activated sites with ou tward and inward ionic currents coherent with what is known of this part of the primary auditory pathway. That is, anatomical sites (neural generators ) and latency for activation matches previous research of the auditory path way. while adding a real time perspective to the anatomical substrates recr uited during the auditory evoked response. An algorithm for calculating the divergent of the vector field, an estimate of the current source density i nside the three-dimensional control volume, was used to infer the possible current sinks and sources generating the field potentials. This technique a llowed a clear visualization of two distinct discharges arising from the la teral lemniscus towards the inferior colliculus, thus recording signal prop agation, as a movie file, with 0.06 ms time resolution. (C) 2001 Elsevier S cience B.V. All rights reserved.