Network activity patterns of corticofugal projection neurons in the auditory cortex
Final Report Abstract
The auditory cortex (AC) is important for higher cognitive functions such as auditory-related learning. It is known that the frequency of perceived sounds is represented in a topographic manner across its different subfields (tonotopy). However, the contribution of different neuron types to this organization has so far not been fully explored. We used two-photon Ca2+ imaging of AC neurons to characterize sound-evoked activity in AC layer 5 in mice. This deep cortical layer contains corticofugal neurons, which project outside of the AC, feeding processed information back to the brainstem. Focusing on corticocollicular (CC) neurons, which project to the inferior colliculus, we observed that this neuron type features a broader, relatively unspecific tuning to sound frequencies, compared to other layer 5 neurons. Furthermore, the tonotopy of CC neurons was found to be quite weak. When using simple as well as complex sounds to evoke activity in the neuronal AC populations, a broad spatial distribution of neurons responding strongly to the same sounds were observed, again indicating a topographically unordered structure of CC neurons. Correlations across the neurons were higher for CC neurons compared to other layer 5 neurons, showing that CC neurons send soundunspecific, but reliable feedback to the auditory brainstem. However, this was only the case for core AC fields. In secondary AC, tonotopy and general topographic organization was either similar between CC and other layer 5 neurons, or even stronger for CC neurons, depending on the analysis approach used. This highlights different roles of specific AC fields in sound analysis and sound-related computation in the brain and implies an important role of CC neurons in learning, which we are exploring in follow-up projects. Overall, we have shown that topographic AC organization is dependent on the neuron type as well as the subfield observed, and that the activity of corticofugal AC neurons features distinct characteristics upon sound stimulation, indicating their importance for auditory processing.
Publications
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Distinct topographic organization and network activity patterns of corticocollicular neurons within layer 5 auditory cortex. Frontiers in Neural Circuits, 17.
Schmitt, Tatjana T. X.; Andrea, Kira M. A.; Wadle, Simon L. & Hirtz, Jan J.
