Age-related changes in neural gap detection thresholds in the rat auditory cortex.

ABSTRACT

The ability of the auditory system to resolve sound temporal information is crucial for the understanding of human speech and other species-specific communications. Gap detection threshold, i.e. the ability to detect the shortest duration of a silent interval in a sound, is commonly used to study the auditory temporal resolution. Behavioral studies in humans and rats have shown that normal developing infants have higher gap detection thresholds than adults; however, the underlying neural mechanism is not fully understood. In the present study, we determined and compared the neural gap detection thresholds in the primary auditory cortex of three age groups of rats the juvenile group (postnatal day 20-30), adult group I (8-10 weeks), and adult group II (28-30 weeks). We found age-related changes in auditory temporal acuity in the auditory cortex, i.e. the proportion of cortical units with short neural gap detection thresholds (< 5 ms) was much lower in juvenile groups compared with that in both adult groups at a constant sound level, and no significant differences in neural gap detection thresholds were found between the two adult groups. In addition, units in the auditory cortex of each group generally showed better gap detection thresholds at higher sound levels than at lower sound levels, exhibiting a level-dependent temporal acuity. These results provided evidence for neural correlates of age-related changes in behavioral gap detection ability during postnatal hearing development.