Selective effects of arousal on population coding of natural sounds in primary auditory cortex

In addition to encoding sound stimulus features, activity in primary auditory cortex (A1) is modulated by non-sensory behavioral state variables, including arousal. Here, we investigated how arousal, measured by pupil size, influences stimulus discriminability in A1. To do this, we recorded from populations of A1 neurons in awake animals while presenting a diverse set of natural sound stimuli. In contrast to previous work, the large stimulus set allowed us to investigate effects of arousal across a wide range of sensory response space. Arousal consistently increased evoked response magnitude and reduced pairwise noise correlations. On average, these changes improved the accuracy of the neural code. However, effects varied across stimuli; neural coding was most improved for areas of the sensory space where noise correlations interfered with the sensory discrimination axis. We also found that first-order modulation of evoked responses and second-order modulation of correlated variability acted on distinct neural populations and timescales, suggesting that arousal interacts with multiple circuits underlying activity in A1.