Temporal processing speed in the inferior colliculus of young and aged rats.

A common problem among the elderly is a difficulty in discriminating speech. One factor that may contribute to this is a deterioration in the ability to process dynamic aspects of speech such as formant transitions. Recently, Mendelson and Ricketts [Mendelson, J.R., Ricketts, C., Hear. Res. 158 (2001) 84-94] showed that cells recorded from the auditory cortex of aged animals exhibited a decrease in temporal processing speed compared to young animals. In the present study, we examined whether this age-related effect was exclusive to the auditory cortex or whether it was apparent subcortically. To this end, single units were recorded from the inferior colliculus (IC) of young and aged rats in response to frequency modulated (FM) sweeps. Results showed that there was no age-related difference in speed or direction selectivity of FM sweep responses in the IC. The present results suggest that the effect of aging on temporal processing speed occurs in the cortex, but not subcortically.