Binaural and commissural organization of the primary auditory cortex of the mustached bat.

In the mustached bat, the primary auditory cortex (AI) can be divided into three subdivisions: the Doppler-shifted constant-frequency processing (DSCF) area, and the anterior (AIa) and posterior (AIp) regions. The DSCF area is composed of two subdivisions: excitatory-excitatory (E-E) and inhibitory-excitatory (I-E). The E-E division is located in the ventral portion of the DSCF area and mainly consists of neurons excited bilaterally, while the I-E division is located in the dorsal portion and mainly consists of neurons which are inhibited by ipsilateral ear stimuli, but excited by contralateral ear stimuli. The E-E division is bilaterally connected by commissural fibers, while the I-E division is not. The AIa and AIp regions have neither E-E neurons nor commissural connections. In the AI of the cat, E-E and I-E neurons form alternating bands which are parallel to the frequency axis. E-E bands are bilaterally connected by commissural fibers, but I-E bands are not. The DSCF area shares a similar functional organization with the AI of the cat.