Characterizing superior colliculus inputs to midbrain dopamine centers in cue learning

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PROJECT SUMMARY Animals exist in complex, sensory rich environments. Certain environmental stimuli (i.e. cues) predict beneficial outcomes (i.e., rewards) that are crucial for survival. In order to appropriately respond to these predictive stimuli, we must be able to discriminate these cues from other sensory input and learn the value of the rewards they predict, during cue-reward learning. Understanding the neural circuits underlying these processes is critical, as disordered sensory processing is a hallmark of several psychiatric diseases such as ADHD and substance use disorders. Dopamine (DA) neurons in the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) are critical in cue-reward learning, but it is not understood how these regions integrate sensory information about cues to drive unique aspects of conditioned behavior. The superior colliculus (SC), which receives input from the retina, has been shown to drive DA neuron activity in response to visual stimuli, and disrupting the SC can prevent DA activity and conditioned responding to visual cues. The anatomy and function of SC projections to the VTA/SNc in cue-reward learning is not known. To address this gap in knowledge, I will characterize the anatomical and functional connectivity of the SC to VTA/SNc circuit (Aim 1) and determine the contributions of SC projections during visual cue learning (Aim 2). To study the topography of this circuit, I will trace distinct pathways from the SC to either the VTA or SNc and determine the projection targets of the neurons that receive SC input. To determine the functional connectivity of SC inputs onto the VTA and SNc, I will excite SC projections via optogenetics while recording the activity of DA neurons in the VTA and SNc through in vivo fiber photometry. These studies will test the hypothesis that the SC drives DA firing via medial to lateral connections on the VTA and SNc. I will also measure and manipulate SC projection activity (using fiber photometry and optogenetics, respectively) during a visual discrimination learning task, to test the hypothesis that SC projections to the DA midbrain augment conditioned behaviors to predictive cues. These studies will reveal how the SC communicates with the VTA and SNc, for fundamental insights into the circuit mechanisms of cue-reward learning.