SUMMARY Auditory receptor cells rely on mechanically gated channels to transform sound stimuli into neural activity. Several TRP channels have been implicated in Drosophila auditory transduction, but mechanistic studies have been hampered by the inability to record subthreshold signals from receptor neurons. Here, we develop a non-invasive method for measuring these signals by recording from a central neuron that is electrically coupled to a genetically defined population of auditory receptor cells. We find that the TRPN family member NompC, which is necessary for the active amplification of sound-evoked motion by the auditory organ, is not required for transduction in auditory receptor cells. Instead, NompC sensitizes the transduction complex to movement and precisely regulates the static forces on the complex. In contrast, the TRPV channels Nanchung and Inactive are required for responses to sound, suggesting they are components of the transduction complex. Thus, transduction and active amplification are genetically separable processes in Drosophila hearing.

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...

Adaptive behavior depends on an animal’s ability to ignore uninformative stimuli, such as repeated presentations of the same stimulus, and, instead, detect informative, novel stimuli in its environment. The primate prefrontal cortex (PFC) is known to play a central role in this ability. However, the neural mechanisms underlying the ability to differentiate between repeated and novel stimuli are not clear. We hypothesized that the coupling between different frequency bands of the local field potential (LFP) underlies the PFC’s role in differentiating between repeated and novel stimuli. Specifically, we hypothesized that whereas the presentation of a novel-stimulus induces strong cross-frequency coupling, repeated presentations of the same stimulus attenuates this coupling. To test this hypothesis, we recorded LFPs from the ventrolateral PFC (vPFC) of rhesus monkeys while they listened to a novel vocalization and repeated presentations of the same vocalization. We found that the cross-frequency coupling between the gamma-band amplitude and theta-band phase of the LFP was modulated by repeated presentations of a stimulus. During the first (novel) presentation of a stimulus, gamma-band activity was modulated by the theta-band phase. However, with repeated presentations of the same stimulus, this cross-frequency coupling was attenuated. These results suggest that cross-frequency coupling may play a role in the neural computations that underlie the differentiation between novel and repeated stimuli in the vPFC.

Abstract. Auditory receptor cells rely on mechanically-gated channels to transform sound stimuli into neural activity. Several TRP channels have been implicated in Drosophila auditory transduction, but mechanistic studies have been hampered by the inability to record subthreshold signals from receptor neurons. We developed a non-invasive method for measuring these signals by recording from a central neuron that is electrically coupled to a genetically-defined population of auditory receptors. We find that the TRPN family member NompC, which is necessary for the active amplification of motion by the auditory organ, is not required for transduction. Instead, NompC sensitizes the transduction complex to movement and precisely regulates the static forces on the complex. In contrast, the TRPV channels Nanchung and Inactive are required for responses to sound, suggesting they are components of the transduction complex. Thus, transduction and active amplification are genetically separable processes in Drosophila hearing.