Coding of tone-pulse amplitude by single neurons in auditory cortex of albino rats (Rattus norvegicus)

We examined the neural representation of tone pulse amplitude in the auditory cortex of anesthetized albino rats. Rate-level functions for monaural, contralateral CF tones were obtained from single neurons. Most of these functions were saturating and monotonic in shape. The dynamic ranges of these functions were typically 5 to 35 dB in breadth, although the tail of this distribution extended to beyond 60 dB. The neurons with the widest dynamic ranges were usually those with the lowest CF thresholds. Nonmonotonic neurons were uncommon, and the nonmonotonicity was not as well developed as that seen in the cortex of cats and monkeys. For two individual rats, data are presented for neurons tuned to the same tone frequency in a single cerebral hemisphere. The CF thresholds of these neurons varied over a 50 dB range, and their collective dynamic ranges spanned at least 70 dB. These data provide a minimum estimate of the dynamic range of the cortical code for tone pulse amplitude in the rat. They suggest that there may be no serious mismatch between the neural and behavioral amplitude dynamic ranges.