Vision, choice, action and behavioural engagement arise from neuronal activity that may be distributed across brain regions. To delineate the spatial distribution of neurons underlying these processes, we used Neuropixels probes to record from approximately 30,000 neurons in 42 brain regions of mice performing a visual discrimination task. 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.
Distal brain areas must coordinate their activity in order to execute everyday behaviors, but many neural recording methods are limited to recording from either a small number of local neurons, or proxies of brain activity in global networks. By using widefield imaging to record from large swaths of dorsal cortex in headfixed, behaving animals, researchers can survey cortical areas involved in a variety of cognitive tasks in an unbiased manner. We'll go over the benefits and drawbacks of widefield imaging, discuss practicalities, how to design experiments that make best use of this method, and how to handle resulting datasets.