PROJECT SUMMARY Understanding sensory processing in the brain has been difficult due to the complex and variable nature of neuronal activity. The primary goal of this training proposal is to determine how visual encoding is modulated by fluctuating brain-wide activity. The primary visual cortex (V1) is thought of as the key locus of visual processing. Recent evidence suggests that visual information exists even outside of the traditional visual pathway. Additionally, sensory encoding in V1 is modulated by externally measured behavioral state and locomotion. It remains unclear how these variables are reflected in neuronal computations and to what degree they modulate visual processing and behavior. We hypothesize that trial-to-trial variability in V1 reflects the fluctuating activity of a distributed network of brain regions. In Aim 1, I will use Neuropixels 2.0 recordings to map diverse brain areas and assess their relationships with fluctuating sensory encoding in V1. Aim 2 will determine the fundamental underlying noise level of neurons in V1, providing a key metric for understanding the fidelity of visual encoding and for models used to analyze neural data. Together, these aims will advance our understanding of the nature of visual cortical encoding and the distributed network of brain regions that support visual processing and behavior. These results will improve our ability to create more effective brain-computer interface therapeutics, which currently rely on an incomplete understanding of information coding in the brain. During my tailored training period, I will learn Neuropixels electrophysiology, advanced computational analysis techniques, and whole-brain histological processing and imaging under the guidance of experts in a supportive training environment. These skills will prepare me for an independent career as a neuroscientist working to advance the understanding of brain function and behavior.