Evoked potentials to auditory probes as indices of cerebral specialization of function--replication and extension

This study was an attempt to replicate findings from previous work in our laboratory as well as to study the relationship between vertex-referenced and linked mastoid-referenced responses under conditions purported to produce differential hemispheric activation. Auditory evoked potentials were recorded between T4-Cz, T3-Cz, T4-A1A2, and T3-A1A2 to task-irrelevant tone pips superimposed on a baseline condition and on two experimental conditions (verbal and music) hypothesized to differentially activate areas of the left and right cerebral hemispheres. Significant AEP amplitude asymmetries were obtained as a function of the ongoing tasks, replicating our previous findings. Higher amplitude AEPs were recorded from temporal-to-vertex leads from the hemisphere thought to be most involved in the ongoing task. In addition, temporal-linked mastoids placements showed an effect opposite to that seen for the vertex-referenced leads with lower amplitude AEPs occurring from the hemisphere purported to be most activated by the task. Mastoid-referenced placements were also less sensitive to task effects than vertex-referenced placements.