Age-related changes in auditory spatial properties of the guinea pig superior colliculus

The map of auditory space located in the deep layers of the guinea pig superior colliculus (SC) is a complex computational representation of the auditory azimuth surrounding the animal. The map undergoes a protracted developmental profile during the first postnatal month and remains plastic until well into adulthood. However, there are no data concerning the state of the collicular auditory space map in much older animals. Multi-unit responses to broadband noise stimuli presented around the azimuthal plane under anechoic conditions were recorded from the deep SC of guinea pigs of a variety of ages, up to 44 months. The data obtained show that the map remains stable up to the age of approximately 36 months. However, after this age, the map shows rapid deterioration and at 42 months, multi-unit responses did not show features consistent with a normal map. It appears that deficits accruing within the central auditory system with increasing age, combine to overcome the ability of the mechanisms of plasticity responsible for space map maintenance to keep pace with the changes, resulting in degraded SC spatial tuning with increasing age.