Movement-related activity dominates cortex during sensory-guided decision making

An animal’s movements and internal state generate an “internal backdrop” of activity that is dynamically modulated. During behavior, this internal backdrop interacts with signals arising from incoming sensory stimuli and may have a substantial impact on task-related computations, like those underlying decision-making. To understand the joint effects of internal backdrop and task-imposed variables, we measured neural activity across the entire dorsal cortex of task-performing mice. We characterized internal backdrop using multiple measures of self-generated parameters including pupil diameter, whisking and body motion. Surprisingly, internal backdrop dominated neural activity across the entire cortex, dwarfing task-related variables and even sensory stimuli. Single neurons in frontal cortex were likewise dominated by internal backdrop. A linear model allowed us to account for multiple dimensions of internal backdrop and uncover hidden signatures of task-related activity. We show that complex, ongoing behavior fundamentally shapes neural activity throughout cortex and must be accounted for when studying decision-making. Highlights We imaged cortex-wide neural activity during auditory and visual decisions in mice. Cortical activity was surprisingly similar during sensory-guided versus random decisions. Movement and state variables vastly outperformed task variables in predicting neural activity. A linear model revealed hidden task-related activity in brain areas and single neurons.