MESENCEPHALIC AUDITORY REGION OF THE BULLFROG

Abstract

[image] The normal cyto-architectonic structure of the midbrain was studied. On the basis of thionin-stained serial sections, the torus semicircularis is divided cytoarchitecturally and topographically into 5 components; the tegmental nuclear group is divided into 4 components. In 25 bullfrogs, anesthetized with urethan and artificially respired, an attempt was made, using microelectrodes, to determine the anatomical limits of the region in the midbrain activated by sound or vibratory stimuli and to determine functional anatomical organization within the active region. Evidence is presented that the laminar, principal and magnocellular nuclei of the torus semicircularis are all activated by sound stimuli. None of the tegumental nuclei nor nucleus isthmi yielded responses to auditory stimuli in the anesthetized frog. The capacity of some neurons to respond to vibrations and of others to respond to long tones could be correlated with anatomical position. No other functional parameter examined could be correlated with unique anatomical loci within the auditory region.