NORADRENALINE MODULATES SENSORY PROCESSING BY BALANCING EXCITATION AND INHIBITION IN THE SUPERIOR COLLICULUS

To cope efficiently with a constantly changing environment, sensorimotor processing must adapt to animal’s moment-to-moment needs, a function tightly linked to neuromodulatory feedback. The superior colliculus (SC) plays a central role in sensorimotor transformations and receives dense noradrenergic (NA) input from the locus coeruleus (LC), which broadcasts arousal- and stress-related signals across the brain. However, how LC-derived NA shapes SC circuit dynamics and visually guided behavior remains unclear. To address this, we combined slice electrophysiology, in vivo two-photon imaging, and optogenetic manipulations during a visual detection task to examine noradrenergic modulation of SC circuits. Ex vivo recordings revealed cell-type-specific effects on excitation–inhibition balance: excitatory SC neurons (Ntsr1⁺) showed suppressed visually evoked responses with increased inhibitory drive, whereas inhibitory neurons displayed elevated spontaneous activity. Consistent with this, optogenetic activation of LC axons in the SC induced neuronal hyperpolarization and reduced firing, indicating that NA primarily modulates local circuit dynamics rather than amplifying retinal input. In vivo imaging further showed that pharmacological reduction of NA suppresses intrinsic collicular dynamics that our lab has recently linked to perception, suggesting that noradrenergic tone regulates baseline network activity associated with internal state. Together, these results demonstrate that noradrenaline dynamically reconfigures SC circuit balance, providing a mechanism by which internal state shapes the transformation of sensory signals into behavior. Building on this work, we are testing the causal role of NA in perceptual detection and imaging noradrenergic activity using the state-of-the-art NA indicator (nLightG2) to link NA dynamics with SC activity and behavior.​