Auditory target detection in dichotic listening involves the orbitofrontal and hippocampal paralimbic belts

In dichotic listening, two similar, yet different stimuli are presented simultaneously to the left and right ear. When two syllables are presented in this way, they seem to blend and discrimination of syllables presented to one ear is only possible with uncertainty. In this event-related fMRI study, we found that the orbitofrontal and paralimbic belts were involved in target detection in dichotic listening. The posterior orbital gyri bilaterally, the left amygdala, hippocampal formation and the left pregenual paracingulate area (PPA) were activated more strongly during dichotic target detection than during correct rejection of target presence. The right posterior orbital gyrus also showed stronger activation during dichotic compared to diotic target detection. Further analyses showed that the blood oxygen level dependent (BOLD) responses in these areas, with the exception of the right hippocampal formation, varied with the subjective decision on target presence rather than with the physical target presence itself. The left PPA, amygdala and hippocampal formation responded differently to left and right ear target detection, suggesting their involvement in the right ear advantage observed in this task. The data show the importance of the orbitofrontal and hippocampal paralimbic belts for auditory stimulus decision processes based on ambivalent sensory information.