Figure 1.

Circuitry proposed in previous reports to account for the changes in binaural properties of EI cells when inhibition was blocked or the DNLL contralateral to the IC was inactivated. Black lines show excitatory and red lines show inhibitory projections. Lower graphs show changes in IID functions obtained before and while inhibition was blocked. A, EI property is assumed to be inherited from the LSO when there is no change in the IID function while inhibition is blocked at the IC. B, EI property is created in IC from excitatory projections evoked by contralateral stimulation and inhibitory projections from the opposite DNLL that are activated by ipsilateral stimulation. In these cells, blocking GABAergic inhibition at the IC or inactivating the opposite DNLL greatly reduces or completely abolishes the ipsilateral evoked spike suppression and transforms an EI into a monaural cell. C, Hybrid formation of EI properties. In these cells, the EI property is inherited from the LSO, but the inhibitory projections from the DNLL cause spike suppression at lower ipsilateral intensities than those generated by the LSO. Hence, blocking inhibition or reversibly inactivating the DNLL does not abolish the EI property but causes a shift in the IIDs that generate the spike suppression.