The grouping of harmonically related tones into the single percept of pitch is a salient strategy for processing speech and music by our auditory system. Although physiological data has demonstrated that information necessary for processing pitch is present in subcortical areas, how pitch is processed or represented in cortex remains unknown. We plan to investigate neural mechanisms underlying pitch representation in the auditory cortex of awake marmoset monkeys (Callithrix jacchus). In particular, we will focus on the rostral field (R), a second core area neighboring primary auditory cortex (AI) that remains relatively unexplored and may play an important role in processing pitch. First, we will use narrowband click trains to investigate rate modulation as a possible explicit encoding mechanism of pitch in AI and R for stimuli with unresolved harmonics. Next, we will use harmonic and inharmonic complex tones to investigate rate modulation as a possible explicit encoding mechanism of pitch in AI and R for stimuli with resolved harmonics. If such a mechanism is used, we will determine if a neuron's preferred pitch is topographically organized. In addition, we will investigate spike synchronization between neurons responding to different harmonics of a common pitch, as a potential implicit encoding mechanism of pitch. Our hypothesis is that AI processes general spectral and temporal information, while neural activity in field R is more specifically related to pitch.
