Functional mapping of auditory responses to complex sounds under light anesthesia in rhesus macaques.

We investigated the auditory responses of anesthetized rhesus macaques to complex natural sounds using functional magnetic resonance imaging (fMRI) and a near-awake anesthesia protocol combining low-dose sevoflurane and dexmedetomidine. Eleven animals were scanned while listening to macaque vocalizations and non-vocal sounds. Robust activation was observed in primary and belt auditory cortices as well as subcortical structures, indicating preserved auditory responsiveness under anesthesia. However, unlike in awake animals, selective responses to vocalizations in anterior temporal voice areas (aTVAs) were absent. Instead, vocalization sensitivity emerged in the ventral premotor cortex, prefrontal cortex, and posterior middle temporal gyrus, regions associated with the dorsal auditory stream and multisensory integration. These findings suggest that while anesthesia preserves basic auditory processing, it modulates higher-order cortical responses involved in voice perception. Anesthetized fMRI thus offers a valuable tool for large-scale studies of primary auditory functions, while it must be approached with caution when studying higher-order auditory functions.