What is the role of the lateral superior olive (LSO)?

• A. Receives excitatory input from the ipsilateral ear and inhibitory input from the contralateral ear.
• B. Detects ITD as a time difference
• C. Receives inhibitory input from the ipsilateral ear and excitatory input from the contralateral ear.
• D. Receives inhibitory input from both ears

Answer: (A)

The lateral superior olive encodes interaural level differences by comparing excitation and inhibition from the two ears. It receives excitatory input from the ipsilateral ear through the ventral cochlear nucleus and inhibitory input from the contralateral ear via the medial nucleus of the trapezoid body (MNTB), delivering glycinergic inhibition. This setup means that a louder sound on the same side as the cell yields stronger excitation relative to inhibition, producing a higher firing rate on that side and signaling the sound’s location. This ILD computation is especially important for localizing high-frequency sounds. The other described patterns would align more with different binaural cues—interaural time differences are processed mainly by the MSO.