Spatial representation in auditory cortex of marmoset monkey.

摘要

One of the fundamental tasks of the auditory system is to determine the spatial location of the acoustic stimulus. Although lesion studies suggest that the auditory cortex is essential for normal sound localization behavior, the role of auditory cortex in spatial hearing is still not well understood. In this thesis, we investigated the spatial tuning properties of neurons in the auditory cortex of awake marmosets. Compared with previous studies, our work explored the acoustic space more completely by using a speaker array covering the whole 360° space.;Cortical neurons' firing rates were modulated by the sound-source location and their spatial receptive fields (SRF) were distributed across the whole 360° space. Most neurons preferred the contralateral locations and the distribution of preferred location azimuths peaked around contralateral 90°. Spatial receptive fields of most neurons didn't show significant changes across different sound levels or stimulus types. Neurons with broad and sharp tuning were both observed while a big proportion of neurons were sharply tuned and only responded to one speaker location. Neurons in the caudal area and belt area were more sharply spatially tuned. Neurons' SRFs were not topographically organized in the auditory cortex.;One of the possible reasons for the lack of a cortical space map is that the spatial representations in the auditory cortex are dynamic. To test this hypothesis, we applied different speaker presentation modes and compared neural responses under different conditions. In contrast to neural adaptation, when sounds were continuously delivered from one location, neurons' firing rates increased significantly and the higher activities often persisted for multiple consecutive trials. This response enhancement was not accompanied by the increase of spontaneous activity and was sensitive to the presentation continuity of the test speaker. The total duration of the facilitated response was much longer when the test speaker was off the peak of the spatial tuning curve measured using the equal-probability presentation mode. Stimulus parameters other than the sound source location, such as the sound level, did not seem to have similar effects on this facilitation process.