This project seeks to improve our understanding of the neural basis for acoustic communication in the auditory cortex of higher mammals. Compared to visual and somatosensory cortex, our knowledge about the organization of auditory cortical areas is much poorer, although they are highly important for the processing of acoustic communication signals. We have started a new attempt to analyze the neural code for auditory processing in nonprimary auditory cortex. In addition to pure tones, standardized complex sounds were used for the stimulation of single neurons. Frequency-modulated (FM) sounds, as they occur in many natural vocalizations, were generated on a digital computer and presented to neurons in the anterior auditory field (AAF) in cats. Complex quasi-natural sounds were also recorded digitally and played back for stimulation. Neurons in AAF responded best to highly transient stimuli with a fast rate of frequency modulation, and AAF may therefore be involved in the processing of spatial aspects in audition. In macaque monkeys, the same approach was taken to explore the multiple auditory maps in nonprimary auditory cortex. Neurons in the rostro-lateral area (RL) responded preferentially to low-frequency sounds, as they are contained in communication signals. By contrast, neurons in the caudo-medial area (CM) preferred high frequencies, which are important for sound localization. Lesioning of primary auditory cortex (AI) seemed to affect responses in area CM more than it did in area RL, which could be due to the different input of these two areas from the medial geniculate nucleus (MGB) of thalamus. CM may depend more on input from AI, while RL (like AI) receives direct input from the parvocellular layers of MGB.