| Frequency-modulated (FM) are important components of animal vocalizations, human speech, and music. The representation of these important sounds in the auditory cortex of awake animals remains unknown, as do the effect of background noise on the representation of these sounds. Here, we determine the encoding of FM sweeps in primary auditory cortex (AI) of awake squirrel monkeys. We also examine the effects of varying the level of a white noise masker on the responses of AI neurons to FM sweeps. We find that FM sweeps are represented differently in different populations of neurons. Some neurons have sustained responses and a rate code for FM sweeps while others have brief responses and a temporal code. Background noise produced a variety of effects on the responses of AI neurons to FM sweeps. While noise degraded the responses of some neurons, the responsiveness of many AI neurons increased in the presence of noise. These results advance our understanding of the processing of frequency modulations in auditory cortex. |
