Auditory cortex shapes sounds responses in the inferior colliculus

The extensive feedback from the auditory cortex (AC) to the inferior
colliculus (IC) supports critical aspects of auditory behavior, but has
not been extensively characterized. Previous studies demonstrated that
activity in IC is altered by focal electrical stimulation and
pharmacological inactivation of AC, but these methods lack the ability to
selectively manipulate projection neurons. We measured the effects of
selective optogenetic modulation of cortico-collicular feedback
projections on IC sound responses in mice. Activation of feedback
increased spontaneous activity and decreased stimulus selectivity in IC,
whereas suppression had no effect. To further understand how microcircuits
in AC may control collicular activity, we optogenetically modulated
different cortical neuronal subtypes, specifically parvalbumin-positive
(PV) and somatostatin-positive (SOM) inhibitory interneurons. We found
that modulating either type of interneuron did not affect IC sound-evoked
activity. Combined, our results identify that activation of excitatory
projections, but not inhibition-driven increases in cortical activity,
affects collicular sound responses.