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Vision, choice, action and behavioural engagement arise from neuronal activity that may be distributed across brain regions. Here we delineate the spatial distribution of neurons underlying these processes. We used Neuropixels probes1,2 to record from approximately 30,000 neurons in 42 brain regions of mice performing a visual discrimination task3. Neurons in nearly all regions responded non-specifically when the mouse initiated an action. By contrast, neurons encoding visual stimuli and upcoming choices occupied restricted regions in the neocortex, basal ganglia and midbrain. Choice signals were rare and emerged with indistinguishable timing across regions. Midbrain neurons were activated before contralateral choices and were suppressed before ipsilateral choices, whereas forebrain neurons could prefer either side. Brain-wide pre-stimulus activity predicted engagement in individual trials and in the overall task, with enhanced subcortical but suppressed neocortical activity during engagement. These results reveal organizing principles for the distribution of neurons encoding behaviourally relevant variables across the mouse brain.
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Performing a perceptual decision involves processing sensory information, selecting actions that may lead to reward, and executing these actions. It remains unknown how the neurons mediating these processes are distributed across brain regions, and whether they rely on circuits that are shared or distinct. Most studies of action selection (hereafter referred to simply as choice) have focused on individual regions, such as frontal, parietal and motor cortex, basal ganglia, thalamus, cerebellum and superior colliculus4-11. However, neural correlates of movements, rewards, and other task variables have been observed in multiple brain regions, including in areas previously identified as purely sensory12-24. It is therefore possible that many brain regions also participate in action selection. Nevertheless, neuronal signals that correlate with action do not necessarily correlate with choice. To carry choice-related signals, a brain region must contain neurons whose firing selectively predicts the chosen action before the action occurs25.
Successful performance in a perceptual task depends not only on choosing the correct action, but also on choosing to engage in the task in the first place. Stimuli that drive actions during an engaged behavioural state do not necessarily drive actions when disengaged; for example, in contexts where the action will not lead to reward. Furthermore, even well-trained participants often show varying levels of behavioural engagement or vigilance within a task,...