The neural computations that underlie the processing of auditory-stimulus identity are not well understood, especially how information is transformed across different cortical areas. Here, we compared the capacity of neurons in the superior temporal gyrus (STG) and the ventrolateral prefrontal cortex (vPFC) to code the identity of an auditory stimulus; these two areas are part of a ventral processing stream for auditory-stimulus identity. Whereas the responses of neurons in both areas are reliably modulated by different vocalizations, STG responses code significantly more vocalizations than those in the vPFC. Together, these data indicate that the STG and vPFC differentially code auditory identity, which suggests that substantial information processing takes place between these two areas. These findings are consistent with the hypothesis that the STG and the vPFC are part of a functional circuit for auditory-identity analysis.

Spatial and non-spatial sensory information is hypothesized to be evaluated in parallel pathways. In this study, we tested the spatial and non-spatial sensitivity of auditory neurons in the ventrolateral prefrontal cortex (vPFC), a cortical area in the non-spatial pathway. Activity was tested while non-human primates reported changes in an auditory stimulus' spatial or non-spatial features. We found that vPFC neurons were reliably modulated during a non-spatial auditory task but were not modulated during a spatial auditory task. The degree of modulation during the non-spatial task correlated positively with the monkeys' behavioral performance. These results are consistent with the hypotheses that the vPFC is part of a circuit involved in non-spatial auditory processing and that the vPFC plays a functional role in non-spatial auditory cognition.non-spatial processing ͉ spatial processing ͉ vocalization A n important conceptual model in auditory neuroscience is that spatial (i.e., location) and non-spatial (i.e., sound type) information are processed in parallel processing streams (1-7). A ''dorsal'' pathway is preferentially involved in the processing of the location of a stimulus. A ''ventral'' pathway is preferentially involved in differentiating between sound types. The dorsal (spatial) pathway begins in the caudolateral belt of the auditory cortex and projects to the regions of the caudal dorsolateral prefrontal cortex. The ventral (nonspatial) auditory pathway begins in the anterolateral belt region of the auditory cortex, which projects to the ventrolateral prefrontal cortex (vPFC).There is a great deal of electrophysiological data supporting this parallel-processing scheme in the auditory cortex. Neurons in the caudolateral belt are more sensitive to stimulus location than those in the anterolateral belt (8-10). Furthermore, neural activity in these dorsal areas is sufficient to account for an animal's psychophysical performance on a sound-localization task (11-13). In contrast, neurons in the anterolateral belt are more sensitive to the changes in stimulus type of an auditory stimulus than those in the caudolateral belt (8-10).Although there is plenty of evidence from human-imaging studies for an extension of parallel functional streams into the parietal and prefrontal cortex (6), evidence from animal studies for selective processing in these structures is more limited. For example, single-unit studies have shown that vPFC and parietal neurons are modulated by both the location and the type of an auditory stimulus (14, 15). In contrast, other single-unit studies have found specialized representations for species-specific vocalizations (7,16,17). Thus, more evidence is needed to support the parallel-stream hypothesis in the PFC of nonhuman primates.One possible explanation for the described above results is that the passive-listening tasks used in these vPFC and parietal studies (14, 15) do not appropriately engage the neurons in these cortical areas. Indeed, the well-known role of the PFC in executive fun...