Sound-evoked Response Properties of Parvalbumin-expressing Interneurons in Mouse Auditory Cortex: Implications for Inhibitory Gain Control

In auditory cortex, sounds are encoded by neurons ‘tuned’ to specific acoustic features. The sound-evoked response properties of these cells are powerfully shaped by inhibitory synaptic input. All cortical inhibition is provided by local interneurons, which comprise <20% of the cortical population. In contrast to excitatory neurons, inhibitory interneurons can be separated into numerous morphologically and neurochemically distinct subclasses. Little is known about the sound-evoked response properties of different types of inhibitory interneurons, as conventional in vivo recording techniques provide limited information about the identity of recorded neu- rons. Here, we identified neurons as members of the Parvalbumin (PV) expressing inhibitory subclass through light-activation of an optogenetic ‘tag’ (channelrhodospin-2), and measured their receptive field properties. In mouse visual cortex, PV neurons are found to be broadly tuned for orientation and respond more gradually to increasing stimulus intensity than principal neurons. In contrast, our preliminary results indicate that auditory PV neurons are well-tuned for sound frequency and have significantly steeper intensity- response functions than principal neurons. Recent studies have shown that PV interneurons in both cortices function to modulate the gain of principle cells without affecting their tuning. The differences we observe in their response properties may allow them to scale tuned responses in auditory and visual cortex, in identical ways.