Locus coeruleus activation transforms cortical taste representations

Abstract

Norepinephrine neurons in the locus coeruleus (LC) shape sensory responses across the brain, yet how LC activity reorganizes population representations of behaviorally relevant sensory attributes remains unclear. We addressed this question in the primary gustatory cortex (GC), a system largely unexplored in neuromodulation research and well-suited for linking sensory coding to affective value. Using miniscope calcium imaging in awake mice combined with optogenetic LC activation, we tested how phasic and tonic LC activity modulate GC encoding of three taste attributes: palatability, mixture ratio, and intensity. Phasic LC activation enhanced correlations between neuronal responses and tastant palatability and expanded the dynamic range of taste representations along a palatability-relevant axis. This expansion was driven primarily by an aversive shift in the representation of all tastants except sucrose, the most palatable stimulus. For mixture ratio and concentration, LC activation induced both stretching and rotation of attribute axes, potentially reflecting dependencies between these attributes and palatability. Analysis of LC-induced changes in neuronal tuning revealed that these population-level transformations likely arise from a combination of multiplicative gain modulation and flexible, tastant-specific changes in tuning. In contrast, tonic LC activation engaged fewer GC neurons and did not produce stretching along any attribute axis, demonstrating that LC effects on population coding depend on activation pattern. Together, these findings provide causal evidence that phasic LC activation reshapes GC population geometry to preferentially enhance palatability encoding, establishing a framework for understanding how neuromodulation may bias taste representations relevant to feeding behavior.