Severing the intercollicular commissure prevents bilateral disruption of the map of auditory space in the superior colliculi following monocular enucleation

Abstract

A previous study demonstrated that developmental monocular enucleation resulted in bilateral disruption of the formation of the auditory space map in both superior collculi, even though only one colliculus had been deprived of visual input. The present study found similar map disruption, when monocular enucleation was carried out following the initial emergence of the map at 32 days after birth. The study also investigated the effect of monocular enucleation plus simultaneous transection of the intercollicular commissure (a recognised pathway for communication between the colliculi). Multi-unit responses to free-field auditory stimuli were recorded from both colliculi of the two experimental groups. In the group which had later monocular enucleation alone, the auditory responses were disrupted in a manner very similar to those recorded from animals which had undergone early monocular enucleation. Similarly, in the group in which the collicular commissure had been severed at the time of monocular enucleation, the auditory responses were also disrupted in the colliculus contralateral to the enucleation. In contrast, the colliculus ipsilateral to the enucleation exhibited normal, topographically organised, auditory responses. Thus, severing the intercollicular commissure at the time of monocular enucleation protected the map of auditory space in the ipsilateral colliculus.