The role of the interhemispheric pathway in hearing.

The corpus callosum consists of heavily myelinated fibres connecting the two hemispheres. Its caudal portion and splenium contain fibres that originate from the primary and second auditory cortices, and from other auditory responsive areas. The anterior commissure in humans is much smaller than the corpus callosum, and it also contains interhemispheric fibres from auditory responsive cortical areas. The corpus callosum is exclusively present in placental mammals, while in acallosal mammals, most of the corpus callosum-related functions are carried out by the anterior commissure. The exact contribution of these two structures and of interhemispheric transfer in hearing in humans is still a matter of debate. In more recent years, human behavioural studies which employ psychoacoustic tasks designed to tap into interhemispheric transfer, combined with sophisticated neuroimaging paradigms, have helped to interpret information from animal experiments and post-mortem studies. This review will summarize and discuss the available information of the contributions of the human interhemispheric pathway in hearing in humans from behavioural, neuroimaging and histopathological studies in humans.