Perception is inherently variable; the same external stimulus might be detected or missed in different instances. Neuronal signals governing this variability remain elusive. Past studies have shown that mice can be trained to report optogenetic stimulation of primary somatosensory cortex (S1), bypassing the trial-by-trial perceptual variability associated with external stimuli. These studies, however, stimulated different populations of S1 neurons on different trials which may also contribute to perceptual variability. Our aim is to use spatial light modulation (SLM) to stimulate the same S1 neurons across trials and investigate how perception of such a highly-controlled stimulus is represented brainwide. To achieve this, the first approach was to establish a 2-photon stimulation paradigm that does not suffer from opsin desensitization. Our data indicates that imaging GCaMP at 920 nm has cross-talk with the gold-standard opsin for all-optical experiments, C1V1. Consequently, varying the imaging paradigm may ameliorate opsin desensitization and facilitate reliable stimulus-evoked activity with an SLM. The second approach was to use Neuropixels to record signals from multiple brain regions in mice whilst they reported optogenetic stimulation of S1, delivered using an LED through a cranial window. We are currently analyzing this data to investigate how downstream neuronal signals transform S1 activity into goal-directed actions. We will be bringing these lines of inquiries together, examining the relationship between trial-by-trial perception of spatially controlled S1 stimulation and downstream neuronal signals. Our results offer improved protocols for all-optical experiments, and will provide a spatio-temporally precise brainwide understanding of neuronal signals underlying perception.